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Chemistry 2202 Unit 2: Organic Chemistry Notes taken form CDLI.ca website Literally thousands of new substances are discovered or synthesized each year. Some estimates suggest that the number is about 250,000 new compounds! The vast majority of these compounds contain carbon. The study of carbon compounds is called organic chemistry. It is an important component of other areas of study including, but certainly not limited to, biochemistry, bioengineering, chemical engineering, forensics, medicine, and pharmacology. Carbon compounds are derived from fossil fuels like crude oil, natural gas, and coal, living things like plants and animals, and invention. Plastics, fuels, and pharmaceuticals are just some of the many different substances you encounter each day that originate from naturally occurring or synthesized organic matter. There is a strong connection between industry and organic chemistry. Clothing fibers like nylon, spandex, lycra, polyester, rayon and acrylic, plastics of all types like the clear plastic bottle of water or soft-drink in your lunch bag, soaps, cleaners, pain killers, bug repellent, engine coolant, windshield washer fluid, transmission fluid, brake fluid, refrigerator and air conditioner coolants ... the list goes on for pages and pages ... all of these are the products of industry founded on the study of organic chemistry. In this unit you will be introduced to the fundamental concepts of organic chemistry. Throughout this unit, take time to reflect on how the study of organic chemistry leads to development of technologies and how those technologies impact upon society and the environment. A Brief History of Organic Chemistry Organic chemistry is the study of compounds that contain carbon. It is one of the major branches of chemistry. The history of organic chemistry can be traced back to ancient times when medicine men extracted chemicals from plants and animals to treat members of their tribes. They didn't label their work as "organic chemistry", they simply kept records of the useful properties and uses of things like willow bark which was used as a pain killer. (It is now known that willow bark contains acetylsalicylic acid, the ingredient in aspirin - chewing on the bark extracted the aspirin.) Their knowledge formed the basis of modern pharmacology which has a strong dependence on knowledge of organic chemistry. Page 1 of 88 Organic chemistry was first defined as a branch of modern science in the early 1800's by Jon Jacob Berzelius. He classified chemical compounds into two main groups: organic if they originated in living or once-living matter and inorganic if they came from "mineral" or non-living matter. Like most chemists of his era, Berzelius believed in Vitalism - the idea that organic compounds could only originate from living organisms through the action of some vital force. It was a student of Berzelius' who made the discovery that would result in the abandonment of Vitalism as a scientific theory. In 1828, Frederich Wöhler discovered that urea - an organic compound - could be made by heating ammonium cyanate (an inorganic compound). Wöhler mixed silver cyanate and ammonium chloride to produce solid silver chloride and aqueous ammonium cyanate: He then separated the mixture by filtration and tried to purify the aqueous ammonium cyanate by evaporating the water. To his surprise, the solid left over after the evaporation of the water was not ammonium cyanate, it was a substance with the properties of urea! Wöhler's observation marked the first time an organic compound had been synthesized from an inorganic source. Page 2 of 88 inorganic organic A Turning Point in Science History Wöhler's discovery was a turning point in science history for two reasons. First, it undermined the idea of Vitalism because an organic compound was produced from an inorganic one. However, it also represented the discovery of isomerism - the possibility of two or more different structures (ammonium cyanate crystals and urea crystals) based on the same chemical formula (N2H4CO). Chemists started searching for reasons to explain isomerism. That in turn led to theories about the structure of chemical compounds. By the 1860's, chemists like Kékulé were proposing theories on the relationship between a compound's chemical formula and the physical distribution of its atoms. By the 1900's chemists were trying to determine the nature of chemical bonding by developing models for electron distribution. During all of this time the number of known organic compounds was increasing rapidly year by year. During the 20th century, organic chemistry branched into sub-disciplines such as polymer chemistry, pharmacology, bioengineering, petro-chemistry, and numerous others. During that century, millions of new substances were discovered or synthesized. Today over 98% of all known compounds are organic. Your study of organic chemistry begins at a time when the number of organic compounds and the number of reactions they undergo is nothing short of bewildering! Your study of organic chemistry begins with a study of the classification system, naming rules, and some key reactions that organic compounds undergo. Sources of Organic Compounds There are three generally accepted sources of organic compounds: carbonized organic matter living organisms invention/human ingenuity Carbonized Organic Matter: Coal, Oil, and Natural Gas Page 3 of 88 Hundreds of millions of years ago, the organisms that inhabited earth were quite different than those we find here today. Plants were fast growing and lacked the woody tissues associated with the trees that currently dominate the world's productive ecosystems. Giant plants with broccoli-like stems grew rapidly, died, and decayed to form rich organic soils upon which more and more plants grew. Eventually, thick layers of decomposing organic matter accumulated in much the same way that peat bogs do today. Over time these massive organic layers were buried under sediment, rock, or ice where they were subjected to tremendous pressures. In this way, they were transformed into various types of coal. Meanwhile in Earth's prehistoric shallow seas, simple organisms like algae, bacteria and zooplankton thrived. As these tiny organisms died, they formed thick layers of organic matter on the sandy bottoms of these seas. Compression of layer upon layer of this material produced rocks known as shale. Under the tremendous pressures from the layers above, and with the shifting of earths tectonic plates, the organic matter trapped in these rocks was converted to oil and natural gas over millions of years. The oil and gas migrated into porous rocks like sandstones or into large pockets of space located kilometres below the earth's surface. Thus organic matter from the past became today's fossil fuels. Humans have known about fossil fuels for over 6000 years; however, only during the past 300 years have they been utilized on a large scale. Coal was the first of the fossil fuels to be extracted from the earth on a commercial basis. It was the fuel that drove the steam engines of the industrial revolution in the 18th, 19th, and 20th centuries. Through a process called destructive distillation, coal was converted into coke, coal tar, and coal gas. Coke was used in the smelting of ores, coal tar was refined into over 200 different carbon compounds, and coal gas was used for things like street lighting! Oil emerged as the dominant energy source for transportation in the 20th century. Natural gas is becoming the clean alternative to coal for generating electricity. It is also widely used as home heating and appliance fuel in North America. The economies of the western world are now completely dependent on oil and natural gas. To summarize, Carbonization refers to the process by which the organic matter in once living plants and animals is reduced. This process simplifies the organic matter and results in the formation of hydrocarbons (crude oil) and coal – fossil fuels. To some people, the burning of fossil fuels represents a tremendous waste. Not only does this practice contribute to the build up of carbon dioxide in the atmosphere, it also Page 4 of 88 consumes that raw materials needed to make useful substances like plastics. By some estimates, the world will virtually exhaust its supply of oil and natural gas by 2050. Nature: Living Organisms Every living organism is a source of organic compounds. Each species is capable of producing a wide range of compounds, some of which are unique to that single species. The scent of a rose, the taste of a strawberry, and the fuzziness of a peach are the results of biochemical manufacturing processes within living things. Given that there are hundreds of thousands of species on earth, nature represents our most important source of organic compounds. Humans have extracted and purified thousands of useful compounds from plants and animals. For example, the penicillin used to fight bacterial infections is extracted from a naturally occurring mold. Acetylsalicylic acid, commonly known as aspirin, comes from the bark of a species of willow tree. Vanilla flavouring is extracted from dried beans that come from a species of orchid called Vanilla planifolia. The list of examples goes on for volumes of pages. Invention Antibiotics, aspirin, vanilla flavouring, and heart drugs are examples of substances that no longer have to be obtained directly from nature. They are manufactured in laboratories from organic starting materials. Furthermore, experiments in which the chemical structures of naturally occurring substances are modified has produced organic compounds substances that do not exist anywhere in nature. Each year over 250,000 new chemical compounds are discovered and many of these are products of scientists' imaginations, exploration, and in some cases - experiments gone wrong! Plastics are excellent examples of substances that are the product of invention - they are not found anywhere in nature. Brief History Textbook Readings page: 318: Organic Chemistry. page: 320: Introduction. pages: 321- 322: Organic compounds: Natural and synthetic. Textbook Items page 323: # 1 page 371: # 9 Page 5 of 88 Sources of Organic Compounds textbook Readings page: 322: The origin of hydrocarbons. page: 323: Sources of hydrocarbons. Textbook Items page 323: # 2 and 3 page 371: # 1 and 8 Why so many carbon compounds? What bonding properties of carbon might account for the tremendous diversity of organic compounds? Have a look at each series of structural formulas. The hydrogen atoms have been omitted from the structural formulas for simplicity - this is standard practice when drawing structural formulas for organic compounds. Look for trends in each series and then respond to the items that follow. Series 1 Series 2 Series 3 Series 4 Page 6 of 88 Series 5 Items to Think About 1. Choose a word to describe the structures in Series 1. What would be the next structure in the series? 2. How do the structures in Series 1 differ from those in Series 2? 3. Choose a word to describe the structures in Series 3. Describe an identifying feature of each member in this series. 4. How do these structures in Series 4 differ from the previous ones? 5. Compare the composition of the molecules in Series 1-4 to those in Series 5. 6. What do you notice about the number of covalent bonds a carbon atom can form? Stability of Carbon to Carbon Bonds Carbon atoms form stable covalent bonds with other carbon atoms. Carbon to carbon bonds are very strong - a lot of energy is required to break them compared to other covalent bonds. The tremendous diversity of organic compounds is due mainly to the ability of carbon atoms to form stable chains, branched chains, rings, branched rings, multiple rings, and multiple bonds (double and triple bonds). Add to this the ability to bond to many other nonmetal atoms, and you can certainly see why organic compounds outnumber all other classes of compounds combined by a huge margin! ISOMERISM: Do you remember the days when you played with building blocks? It was common to build one structure with the blocks, take it apart, and build a completely different structure using the exact same blocks. Page 7 of 88 In chemistry, atoms are the building blocks. Because of carbon's unique bonding properties, it is possible to make a number of different molecules using the same group of atoms. Consider these two structures: butane methylpropane Butane and methylpropane both have the same molecular formula, C4H10. Structures that have the same molecular formula but different structural formulas are called structural isomers. Therefore butane and metylbutane are both structural isomers. The possibility of more than one structure for a single molecular formula is called isomerism. It is a key reason for the tremendous diversity of organic compounds. For example, there are 75 possible isomers of C10H22 Example 1 Using structural formulas, draw all the possible isomers of C5H12. Example 2: Draw all the isomers of C6H14 (hint: there are five possible isomers) Page 8 of 88 Classification of Organic Compounds: It is helpful to divide organic compounds into two major groups based on composition only. The hydrocarbons are compounds that consist of carbon and hydrogen atoms only (e.g. methane, CH4). The hydrocarbon derivatives are compounds in which one or more hydrogen atoms is replaced by another nonmetallic atom (e.g. bromomethane, CH3Br). Hydrocarbons There are two main classes of hydrocarbons: aliphatic and aromatic hydrocarbons. Aliphatic hydrocarbons consist of carbon atoms bonded together in straight chains, branched chains, rings, branched rings, multiple rings or branched multiple rings. Aromatic hydrocarbons are distinguished by the presence of a special group of six carbons known as the benzene ring. Page 9 of 88 Three classes of aliphatic hydrocarbons can be defined based upon carbon to carbon bond type. They are the alkanes, alkenes and alkynes. Note that each term differs from the other two by a single letter. The endings, -ane, -ene, and -yne, indicate the presence of single, double and triple bonds respectively. Non-benzene rings of three or more carbon atoms are known as alicyclic hydrocarbons and these are further classified based on the types of bonding within the rings. Each class of aliphatic hydrocarbons may be represented by a general formula showing the ratio of carbon atoms to hydrogen atoms. Applying these general formulas will assist you in the classification of organic compounds in this course. Table 1: Some general formulas for common classes of aliphatic hydrocarbons. General Formula Class of Hydrocarbon CnH2n+2 alkanes CnH2n alkenes (one double bond) cycloalkanes CnH2n-2 alkynes (one triple bond) cycloalkenes (one double bond) Using General Formulas A general formula can be used to determine the molecular formula of a compound. They can also be used to classify compounds when you are given chemical formulas. Example 1 Write the molecular formula for a 10 carbon alkane. Answer Alkanes have the general formula CnH2n+2 ; therefore, substituting the number of carbon atoms into the general formula, the molecular formula for the compound becomes C10H22. Example 2 Page 10 of 88 Classify C2H4. Answer C2H4 fits the general formula CnH2n. Since a minimum of three carbons are needed to produce a ring structure, C2H4 may be classified as an alkene. Hydrocarbon Derivatives The vast majority of known organic compounds are classified as hydrocarbon derivatives. These compounds contain carbon and some other non-hydrogen element usually a nonmetal. Most, but not all hydrocarbon derivatives also contain hydrogen. You are already familiar with many hydrocarbon derivatives. Gas-line antifreeze (methanol), vinegar (acetic acid), amino acids, and sugars are just some of the numerous organic substances in this group. These compounds are the focus of lesson in later sections. Most hydrocarbon derivatives are classified on the basis of a functional group - an atom or group of atoms that give the compound its unique chemical and physical properties. Example 2 Which substance is classified as a hydrocarbon derivative? NaCl, H2O, C3H8, or C2H5OH? Answer Sodium chloride and water are inorganic compounds because they lack carbon. Propane is a hydrocarbon because it contains carbon and hydrogen and carbon atoms only. Ethanol is a hydrocarbon derivative because in addition to carbon, it contains oxygen. Alkanes and Alkyl Groups Do you recognize these names: propane, butane, and octane? What are these substances used for? How common are they in your community? Alkanes Propane, butane and octane are just three examples of organic compounds that are classified as alkanes. Alkanes are hydrocarbons in which the carbon atoms have single bonds to other atoms. They have the general formula CnH2n+2 where n is a natural number. For example, an alkane containing five carbon atoms (n=5) will have 2n + 2 or 12 hydrogen atoms. Its formula will be C5H12. Page 11 of 88 (Count the number of carbon and hydrogen atoms to convince yourself that the diagram conforms to the general formula for an alkane. Note that in structural formulas for organic compounds the symbols for hydrogen atoms may be omitted.) Methane, CH4, is the simplest alkane - it consists of one carbon atom and four covalently bonded hydrogen atoms. It is a gas at room temperature. It is a product of the decomposition of more complex organic substances that make up living things. It makes up 80% of natural gas. Ethane, C2H6, is the simplest alkane to contain a carbon to carbon bond. It has six hydrogen atoms bonded to these two carbon atoms. It too is found in natural gas. Propane and butane are the next two alkanes in this series. propane: butane: Both are also found in natural gas, but in much lower concentrations than methane and ethane. Can you see a trend in the structures for these four alkanes? By what factor do the structures differ? Page 12 of 88 A series consisting of a group of compounds in which the compounds differ by a constant increment is called a homologous series. The methane, ethane, propane and butane are an example of a homologous series. The nomenclature system for organic compounds is based on sets of prefixes and suffixes. You already know that the suffix "-ane" means single bonded carbon atoms, and you have probably already deduced that meth-, eth-, prop-, and but- mean 1, 2, 3, and 4 respectively. These prefixes are used throughout organic nomenclature, so you must memorize them. Nomenclature (Naming) of Alkanes Table 1: IUPAC prefixes for use in organic nomenclature.(IUPAC = International Union of Pure and Applied Chemistry) meth eth prop but pent hex hept oct non dec 1 2 3 4 5 6 7 8 9 10 Naming Simple Alkanes To name continuous-chain (simple) alkanes from either a chemical or structural formula: make sure that the number of carbon and hydrogen atoms matches the general formula CnH2n+2. count the number of carbon atoms and indicate this number using the appropriate prefix. add the -ane ending to the prefix to indicate that the compound is an alkane. Example 1 Name these continuous-chain hydrocarbons. 1. C6H14 2. C10H22 Answer Page 13 of 88 1. C6H14 matches the general formula for an alkane. It contains six carbon atoms in a continuous chain, so the prefix hex- is added to the suffix -ane to produce the name hexane. 2. C10H22 matches the general formula for an alkane. It contains ten carbon atoms in a continuous chain, so the prefix dec- is added to the suffix -ane to produce the name decane. Drawing Structural Formulas You should be able to draw the structure of any continuous-chain alkane given either its chemical formula or its name. The steps are straight-forward: determine the number of carbon atoms in the molecule by looking at the subscript in the chemical formula. draw the carbon atoms in a straight line. Draw a line between each atom to represent a single covalent bond. draw single lines from carbon atoms to hydrogen atoms. Each carbon atom should have four single bonds and each hydrogen must have just one single bond. Example 2 Draw the structural formula for heptane, C7H16. Answer Draw a chain of seven carbon atoms. Draw lines to represent the bonds to hydrogen atoms. Note that inclusion of the symbols for hydrogen is optional. Condensed Structural Formulas Page 14 of 88 Another common way to represent a hydrocarbon is to use a condensed structural formula. For example, the chemical formula of C4H10 can be represented as: or or (dashes are optional) A condensed structural formula provides more information about the bonds in a molecule than a molecular formula does but it is sometimes harder to interpret than a complete structural formula. Example 3 Write the condensed structural formula for pentane, C5H12. Answer You may find it convenient to draw the full structural formula for the molecule and reduce it to the condensed structural formula. The condensed formula shows each carbon atom with the number of hydrogen atoms bonded to it. or Structural formulas show you the bonds in a molecule, but they cannot represent molecules three-dimensionally. Notice that a carbon "skeleton" is not perfectly straight, but zigzagged. Each carbon atom is bonded to four other atoms. VSEPR theory predicts that each of the single bonds involving carbon points to a corner of a tetrahedron to give bond angles of about Page 15 of 88 109.5°. A carbon chain in which each carbon is bonded to another by single bonds has a zigzagged shape. A really compact way of representing this structure is to use a line drawing. You will use these kinds of drawings when representing alicyclic hydrocarbons in a later lesson. Nonetheless, it is worth noting how these drawings are made in the event that you encounter them in your readings. The end of each segment represents a carbon atom. Single lines represent single covalent bonds. The presence of hydrogen atoms is assumed and bonds to them are not shown. Alkyl Groups Alkyl groups have have the general formula CnH2n+1. They have one less hydrogen atom than a corresponding alkane. For example the methyl group, -CH3, has one less hydrogen than methane, CH4. The prefixes used in alkane nomenclature are the same as those used to name alkyl groups. The suffix for an alkyl group, as you may have gathered, is -yl. Here are the ones you will use frequently - it is a good idea to memorize them: methyl: -CH3 ethyl: -C2H5 or -CH2CH3 propyl: -C3H7 or -CH2CH2CH3 butyl: -C4H9 or -CH2CH2CH2CH3 pentyl: -C5H11 or -CH2CH2CH2CH2CH3 Alkyl groups are examples of substituents: atoms or groups of atoms that replace a hydrogen atom on a chain or ring of carbon atoms. Branched alkanes contain one or more alkyl groups. You can identify the alkyl groups by finding the longest continuous chain and then locating any carbons that do not appear to be part of the chain. Each of the structures below represents a branched alkane. The left and middle structures have one substituent each. The structure on the right consists of five carbons with methyl groups at the second and fourth carbons. Page 16 of 88 Try thinking of the alkyl groups as being like side roads of a major highway. Naming Branched Alkanes Writing a IUPAC name for a structural formula is an important skill to master. It involves following strict sets of rules. Different rules exist for different classes of organic compounds; however, there are two rules that are used throughout organic nomenclature. First, the name of a molecule is based on the longest continuous chain of carbon atoms containing a functional group. Second, lowest possible numbers are used to indicate the location of substituents or functional groups on the continuous chain. Steps to Name a Branched Alkane: 1. Find the longest continuous chain of carbons in the molecule and name it. This is the parent chain of the molecule. Be careful, the longest continuous chain is not always obvious because it may zigzag. (HINT! highlight the parent chain in some way.) 2. Number the carbons in the parent chain. Designate the carbon at the end to which branching is closest as number 1. 3. List the alkyl groups present. 4. If there is more than one type of alkyl group in the molecule you can list their names either in alphabetical order. Page 17 of 88 5. If an alkyl group occurs more than once, use a Latin prefix to indicate the number present. The Latin prefixes are di = 2, tri = 3, tetra = 4, penta = 5, and so on. - e.g. two methyl groups would be represented as dimethyl 6. Use a number to indicate the location of each alkyl group on the parent chain. 7. Use proper punctuation: commas are used to separate numbers, and hyphens are used to separate numbers and letters. Important Points About Naming Branched Alkanes: 1. An alkyl group cannot be located on the terminal carbon of a continuous chain because such an “alkyl” group would serve to extend the chain further. 2. Note that the longest continuous chain may not be obvious, make sure you have located it by testing the length of all possible parent chains! 3. Alkyl groups must be assigned the lowest numbers possible. 4. Adding a prefix to an alkyl group's name does not change its order in the alphabetized listing of alkyl groups in a name. Example 4 Write a IUPAC name to represent this structural formula. Answer 1. Begin by locating the longest continuous chain of carbon atoms. Page 18 of 88 The longest chain is seven carbon atoms long, so the parent chain is heptane. 2. Assign number "1" to the carbon at the end to which branching is closest. Since, branching is closest to the right side, the parent chain is numbered sequentially from right to left. 3. Identify the alkyl groups. There are two: a methyl at carbon #3, and an ethyl at carbon #4. 4. Build the name of the branched alkane. 4-ethyl-3-methylheptane Notice that the alkyl groups are listed in alphabetical order and their locations on the parent chain are indicated using the appropriate numbers. Hyphens separate the numbers from the letters. Notice that the "methyl" and "heptane" become one name. Page 19 of 88 Textbook Readings MHR pages: 332 - 338: Naming alkanes (stop before physical properties). pages: 325 - 326: Representing Structures and bonding. Practice Items 1. Provide a IUPAC name for each structural formula. (a) (b) (c) (d) (e) (f) Page 20 of 88 (g) 2. Draw the structural formula for each alkane. (a) 2,2,4-trimethylpentane (b) 3-methylheptane (c) 3-ethylhexane (d) 3-ethyl-2-methyl-4-propylnonane (e) 2,3-dimethylhexane (f) 4-methylheptane (g) Which alkane in items a-f is not an isomer of C8H18? 3. Draw condensed structural formulas for each of the items in Exercise 2. 4. Draw and name the possible structural isomers of C7H16. Alkenes and Alkynes Page 21 of 88 Have you ever been caught in a heavy rainstorm? One so bad that every stitch of your clothing was soaked with water? Someone seeing you in that condition might say "Umm, my you're saturated!" In organic chemistry, the term saturated refers to organic compounds which contain single carbon to carbon bonds or which have the maximum number of hydrogen atoms bonded to carbon atoms. Alkanes are saturated hydrocarbons. Hydrocarbons whose molecules contain double or triple carbon to carbon bonds (multiple bonds) are said to be unsaturated. Alkenes and alkynes are unsaturated hydrocarbons - they possess at least one double or triple bond respectively. As a result, alkenes and alkynes have a higher carbon to hydrogen ratio than alkanes. Your study of alkenes and alkynes will be restricted to compounds containing only one multiple bond per molecule. This allows you to make the generalization that with each extra shared pair of electrons between two carbons, the number of hydrogen atoms per molecule decreases by two. The general formulas for alkenes and alkynes reflect this generalization. Respectively, they are: CnH2n and CnH2n-2. Naming Alkenes and Alkynes Consider these structural formulas for isomers of C5H10: If you follow the rules introduced in the study of alkanes, then both isomers would be named pentene. Can you see a problem with this? Roll your mouse over each structural formula above to see how IUPAC (International Union of Pure and Applied Chemistry) deals with the issue? When naming alkenes and alkynes, a number is used to designate the location of the multiple bond. In fact, priority in the numbering of the longest continuous chain in unsaturated hydrocarbons is given to the location of the multiple bond. Consider these examples: Page 22 of 88 If the structural formula on the left was named using the rules for branched alkanes, the parent chain would be numbered from right to left and the methyl group would be located at carbon #2. However, since priority is given to the location of the multiple bond, the parent chain is numbered from left to right and the structure is named 4methyl-1-pentene. Can you name the structure on the right? The suffixes -ene and -yne are used to name the parent chains in alkenes and alkynes respectively. Rules for Naming Alkenes and Alkynes The rules for naming alkyl branches in alkenes and alkynes are the same as those introduced when you studied alkanes. Here is a summary of the rules to be applied: 1. Count to find the longest continuous chain of carbon atoms that contains the multiple bond. Number the carbons by giving the multiple bond the lowest possible number. 2. List and number the alkyl groups present. Assign Latin prefixes if necessary. List them alphabetically. (For the purpose of alphabetizing, ignore the prefixes di, tri, etc.) 3. Write the name using proper punctuation. Commas are used to separate numbers, and hyphens are used to separate numbers and letters. Structural Formulas for Alkenes and Alkynes The process of translating the name of an alkene or alkyne into a structural formula requires the same kind of systematic approach introduced in your study of alkanes. Decompose the name from right to left beginning with the name of the parent chain, the location of the multiple bond and then the location(s) of the alkyl group(s). Consider these examples. Example 2 Page 23 of 88 Draw a structural formula for 2-ethyl-1-pentene Answer Begin by drawing the parent chain including the multiple bond. Then add the alkyl group to the appropriate carbon atom. An ethyl group is located on carbon #2. or At first glance, this structure appears to deviate from an important rule - the one about finding the longest continuous chain - because the longest chain is six carbons long. However, it is important to note that in the nomenclature of alkenes and alkynes, priority is given to the location of the multiple bond. This means that when a multiple bond is located between carbons 1 and 2, an ethyl group may be located on carbon #2. Important Notes 1. Be careful when drawing structural diagrams. Make sure that the carbon atoms share only four pairs of electrons in either four single bonds or one double bond and two single bonds or one triple bond and one single bond. 2. Be careful when you are drawing condensed structural formulas for hydrocarbons with multiple bonds. Make sure that each carbon atom is bonded to the correct number of hydrogen atoms. It is a good idea to draw the structural diagram of the compound first, and then draw the condensed structural formula. Structural Isomerism in Alkenes and Alkynes Structural isomerism refers to the possibility of more than one possible structural isomer for a given molecular formula. The presence of multiple bonds increases to the number of possible isomers (structural and other). For example, let's compare C4H10, C4H8, and C4H6. There are two isomers of C4H10, six isomers of C4H8, and at least seven isomers of C4H6. Page 24 of 88 Why does the presence of multiple bonds make such a difference to the number of possible isomers? An obvious reason is possibility of more than one location for the multiple bond. For example, consider 1-butene and 2-butene for C4H8, and 1-butyne and 2-butyne for C4H6. Notice how simply changing the location of a multiple bond results in a different structural isomer? The possibility of branching in C4H8 like and structural isomers. and the existence of ringed structures , and branched rings results in other In alkynes, the electrons in the triple bond may be redistributed to give two double bonds which may be located in various positions in the chain. Other isomers called geometric isomers are possible in alkenes. The labels cis- and trans- are used to distinguish between them. Think of cis as meaning the same side and trans as meaning across. Can you identify the cis and trans isomer? Roll your mouse over each image to check your answers. Page 25 of 88 The important point to remember here is that a simple molecular formula for an unsaturated hydrocarbon can result in a large number of isomers. Recall that this was one of the reasons cited for the tremendous diversity of organic compounds. At this point you will focus on drawing straight chain and branched isomers for alkenes and alkynes. The ringed structures will be described in the next lesson. Example 3 Draw structural formulas for and provide names for five of the possible structural isomers of C6H12. Answer As you will see, there are more than five possible isomers. You can begin deriving them by drawing the straight alkene isomers. This is achieved by moving the location of the multiple bond until all the possible straight-chain isomers are drawn. 1-hexene 2-hexene (there is a trans isomer too) 3-hexene (there is a trans isomer too) Then you can shorten the parent chain by one carbon and use it to form an alkyl group. 2-methyl-1-pentene 3-methyl-1-pentene 4-methyl-1-pentene Page 26 of 88 Move the location of the multiple bond again to derive additional isomers. 2-methyl-2-pentene 3-methyl-2-pentene 4-methyl-2-pentene If the parent is shortened to four carbon atoms, more isomers can be derived. 2-ethyl-1-butene 2,3-dimethyl-1-butene 3,3-dimethyl-1-butene 2,3-dimethyl-2-butene As you can see, one molecular formula can be represented by a large number of structural formulas! Textbook Readings MHR Page 27 of 88 pages: 344 - 348: Alkenes (omit properties for now). pages: 354: Alkynes (omit properties for now). Practice Items 1. Draw a structural formula for each name given. a) 1-pentene b) 2-pentene c) 3-hexyne d) 2-octene e) 4-octyne f) 2-butene 2. Write a IUPAC name for each alkene or alkyne. a) b) CH3CH2CHCHCH3 c) d) CH3CCCH2CH2CH2CH3 Page 28 of 88 e) f) CH3CCCH2CH(CH3)CH2CH3 3. For the molecular formula C5H10 draw and name all of the possible non-cyclic structural isomers. 4. Draw and name three alkyne structural isomers for the formula C5H8. 5. For each compound, provide: i) the IUPAC name or the structural formula ii) the molecular formula iii) the class of hydrocarbon (alkane, alkene, or alkyne) iv) the structural formula and name of one structural isomer a) 4-methyl-1-pentyne b) c) dimethylpropane Page 29 of 88 d) e) f) 2,2-dimethylbutane g) 3-ethyl-2,4-dimethyl-2-pentene h) 3,3-dimethyl-1-pentyne i) j) Cyclic Aliphatics Imagine that you have a chain of three or more carbons. If you remove one hydrogen atom from each of the end carbons, you are left with a pair of bonding electrons that the terminal carbon atoms can share. Can the two end carbons bond to form a ring? A ring of three or more carbons connected by single bonds is called a cyclic alkane or a cycloalkane. Cyclic alkanes have two less hydrogen atoms than their corresponding continuous-chain alkanes. The general formula for a cyclic alkane is CnH2n which is the same as the general formula for an alkene that has one double bond. Page 30 of 88 Cyclic alkenes are rings that possess a double carbon to carbon bond. They are sometimes referred to as cycloalkenes. Cyclic aliphatics may have one or more alkyl groups; however, in this course, you will focus on structures that lack alkyl substituents. Structural Formulas for Cyclic Aliphatics There are at least three acceptable methods of representing a cyclic aliphatic structure: full structural formula, condensed structural formula, and line drawing. All three ways are acceptable, but line drawings are preferred. In a line drawing, each point or corner represents the location of a carbon atom. Example 1 Draw the structural formula for cyclopentane. Answer Draw a ring structure that has five distinct corners. Page 31 of 88 Naming Cyclic Aliphatics To name a cyclic aliphatic: 1. Count the number of carbon atoms in the ring. 2. Name the structure as you would name the corresponding continuous-chain alkane. 3. Add the prefix cyclo to the alkane name. Example 2 Name this cycloalkene. Answer 1. The line drawing has six corners, so the prefix to be used in the name is hex. 2. Since the ring has a double bond, the ending -ene is applied: hexene. 3. Finally, the prefix cyclo- is used to indicate that the carbon atoms form a ring: cyclohexene. Isomerism Cyclic aliphatics are isomers of corresponding aliphatic hydrocarbons. For example cyclobutane is one isomer of C4H8. Other isomers of this molecular formula include 1butene, 2-butene, and methylpropene. Be sure to consider the possibility of a ringed structure when you are asked to draw or list the isomers of any hydrocarbon that possesses three or more carbon atoms. Page 32 of 88 Textbook Readings MHR pages: 356 - 358: Cyclic hydrocarbons - (omit properties for now). Textbook Items MHR page 358: # 30 and 31 page 363: # 6 - 8 page 372: # 17b Practice Items 1. Provide a IUPAC name for each structural formula. a. b. c. 2. Draw a structural formula (line drawing) for each cyclic aliphatic. a. cyclopropane Page 33 of 88 b. cyclopentene c. cyclooctane d. cycloheptene 3. For each cyclic aliphatic in Exercise 2, draw and name one noncyclic isomer. Aromatic Hydrocarbons Imagine how difficult it must be to try to determine the structure of something that you cannot sense directly. This is a predicament that chemists and physicists face all the time. In chemistry we cannot actually see the individual molecules whose structure we are attempting to describe. We use the composition of a substance, our knowledge of bonding theory, and the properties of a substance to predict how the atoms are bonded to each other to form a compound. Some compounds are more difficult to figure out than others. Benzene is a compound that chemists puzzled over for a very long time. Its chemical formula was determined to be C6H6 by Michael Faraday in 1825, but a suitable structural formula wasn't proposed until August Kekulé came up with one in 1865. Kekulé's ring structure was a very significant discovery because it helped explain the unique properties associated with benzene and benzene compounds. Page 34 of 88 Compounds that possess a benzene ring as part of their structure are classified as aromatic compounds. It is the presence of a benzene ring that distinguishes the aromatic hydrocarbons from the aliphatic hydrocarbons. Carbon to Carbon Bonds in Benzene The benzene ring consists of six carbon atoms, each of which is bonded to a hydrogen atom. One way to satisfy the octet rule for carbon atoms in the benzene ring is to show the carbons with alternating single and double bonds. That way, each carbon atom has four bonds: a double bond (C=C), a single bond (C-C), and another single bond (C-H). Now look carefully at the line diagram for the benzene ring above. What do you notice about the single and double bonds? Are they the same length? Double carbon to carbon bonds are 14% shorter than single carbon to carbon bonds, yet x-ray crystallography studies show that all six carbon to carbon bonds in benzene ring are the same length (about 139 pm). The benzene ring is actually a flat hexagonal structure as illustrated by this image. This structure suggests that all six of the carbon to carbon bonds are the same length. In other words, a distorted, unsymmetrical ring is not a suitable model for benzene. Can you think of a way to draw a structural formula that resolves this problem? he problem of producing a structural formula for benzene that is consistent with the flat ring observations has been addressed using the concept of resonance. It is a pretty simple idea. Page 35 of 88 Resonance means that there are two or more possible distributions of bonding electrons for a compound. The resonance structure (sometimes called resonance hybrid) is an average of the electron distributions. Animation requires the flash plug-in. In the case of benzene, the single and double bonds appear to oscillate between two sets of positions. We can represent the resonance hybrid for benzene using a hexagon and an inscribed circle. In benzene, the bonding electrons that make up the double bonds are said to be delocalized. In other words, they do not occupy the same valence orbitals all the time in the way electrons do in typical covalent bonds. The idea of delocalized bonding electrons in the benzene ring is supported by bond length data and by the observation that benzene molecules behave like alkanes in chemical reactions, not like the alkenes. In other words - benzene molecules do not behave as if they have double bonds. (More on the chemical reactions of hydrocarbons later.) Naming Aromatic Hydrocarbons One or more hydrogen atoms of a benzene molecule may be substituted with an alkyl group. The resulting compound is called an alkyl benzene. Although all six of benzene's hydrogen atoms can be replaced by substituents, you will focus on those in which just one or two are replaced. Monosubstituted Alkyl Benzenes A benzene compound in which one hydrogen is replaced by an alkyl group is called a monosubstituted alkyl benzene. Consider these examples: Page 36 of 88 Naming monosubstituted alkyl benzene compounds requires a similar approach to the one you used for simple branched aliphatic compounds. The benzene ring is the parent and the alkyl group is the substituent. The ring carbon where the substituent is located is designated as carbon #1. This number is not included in the name. Using these rules, what are the names of the monosubstituted alkyl benzene's above? Methylbenzene is an ingredient in paint stripper. However, when you pick up a can of paint stripper and look at the ingredients list or the safety sheet, you are more likely to see the non-systematic name toluene. Toluene has been retained as an acceptable name for methylbenzene. Disubstituted Alkyl Benzenes When two hydrogen atoms on the benzene ring are replaced by alkyl groups, the result is a disubstituted alkyl benzene. The two alkyl groups may be the same or different. Consider these examples: What do you notice about the positions of the alkyl groups? What term is used to describe the possibility of three structures for C8H10? What implications might this have for naming? Important Note: Notice that the alkyl groups are numbered using lowest possible numbers. For disubstituted benzenes, there are only three possible combinations: 1 and 2, 1 and 3, and 1 and 4. IUPAC (International Union of Pure and Applied Chemistry) recognizes the use of special letter prefixes for disubstituted benzenes in place of these numbers: ortho means positions 1 and 2. It is represented by an italicized "o". meta means positions 1 and 3. It is represented by an italicized "m". para means positions 1 and 4. It is represented by an italicized "p". Thus 1,2-dimethylbenzene is also known as o-dimethylbenzene. (Note that these letter prefixes are italicized.) Page 37 of 88 As was the case for methylbenzene, non-systematic names have been retained for the three isomers of dimethylbenzene. They are o-xylene, m-xylene, and p-xylene. 1,2-dimethylbenzene = o-dimethylbenzene = o-xylene 1,3-dimethylbenzene = m-dimethylbenzene = m-xylene 1,4-dimethylbenzene = p-dimethylbenzene = p-xylene Naming Aromatic Hydrocarbons A reasonable question to ask now is: "are the rules different if the substituents are different?" The answer is yes and no. No in the sense that you have to assign lowest possible numbers, but yes in the sense that you should number the alkyl groups based on alphabetical order. Example 2 Provide a IUPAC name for this structural formula. Answer 1. Identify the alkyl groups: methyl and butyl. 2. Number the alkyl groups based on alphabetical order and position on the benzene ring: 1-butyl and 3-methyl (roll your mouse over the image above). 3. Combine the names and locations of the substituents with the parent name: 1butyl-3-methylbenzene. When Benzene is the Substituent There are instances when a benzene ring is bonded to a non-terminal carbon of an alkyl group and others where more than one benzene ring is connected to an alkyl group. In these cases, the alkyl groups become the parents and the benzene rings become the branches. Page 38 of 88 As a branch, the benzene ring is called a phenyl group. Textbook Readings MHR pages: 360 - 361: Aromatic hydrocarbons. Textbook Items MHR page 361: # 32 - 35 page 363: # 4, 5, 9 page 371: #17f, 24 Practice Items Exercise 1 Define each term. a. aromatic hydrocarbon b. delocalized electron c. resonance Exercise 2 Provide a IUPAC name for each monosubstituted benzene compounds. a. b. Page 39 of 88 c. Exercise 3 Draw a structural formula for each compound. a. hexylbenzene b. propylbenzene c. pentylbenzene d. octylbenzene Exercise 4 Provide a IUPAC name for each disubstituted benzene compounds. a. b. Exercise 5 Draw a structural formula for each compound. Page 40 of 88 a. 1,2-dipropylbenzene b. o-diethylbenzene c. 1-butyl-4-methylbenzene Exercise 6 For each compound, draw the structural formula or provide a IUPAC name. a. 2-phenylbutane c. 1,1-diphenylethane b. Page 41 of 88 The Petrochemicals The economies of the world are driven by oil and natural gas. Over the past 100 years, agriculture, transportation and manufacturing have evolved to utilize these nonrenewable resources. The demand for products in these sectors of the economy has resulted in a whole new industry called the petrochemical industry. It is difficult to find an aspect of your daily routine that is not in some way tied to the availability of products derived from oil and natural gas. The petrochemical industry has many branches, including: oil and gas exploration oil and gas production oil and gas refining processing of hydrocarbons, and plastics production. Oil Refining and the Properties of Hydrocarbons Think back to when you studied intermolecular forces. What was the relationship between the boiling points of the halogens and the number of electrons per molecule? Let's reconsider this question, but this time let's use the first ten members of the straight-chain alkanes instead. methane - CH4 Methane's boiling point is: -161.0. ethane - C2H6 Ethane's boiling point is: -88.5. propane - C3H8 Propane's boiling point is: -42.0. butane - C4H10 Butane's boiling point is: 0.5. pentane - C5H12 Pentane's boiling point is: 36.0. hexane - C6H14 Hexane's boiling point is: 68.7. heptane - C7H16 Heptane's boiling point is: 98.5. octane - C8H18 Octane's boiling point is: 125.6. nonane - C9H20 Nonane's boiling point is: 150.7. Page 42 of 88 decane - C10H22 Decane's boiling point is: 174.1. What can you conclude about the boiling point of a substance and the size and shape of its molecules? Write your answer below: Crude oil is homogeneous mixture of many different organic compounds. The individual compounds or groups of compounds are called fractions. When crude oil is refined, these miscible fractions are separated from each other. Separation is achieved by heating crude oil so that the various fractions boil off and condense at different heights in a distillation tower (like the ones you see in Come By Chance, NF). This process is repeated over and over in various towers until the crude oil is separated into as many different fractions as possible. The separation of crude oil on the basis of the different boiling points of its fractions is called fractional distillation (or fractionation). Can you relate this process to differences in the strengths of intermolecular forces among the fractions in a crude oil sample? This process is well illustrated and explained in your MHR Chemistry text on pages 366 - 367. Combustion Reactions Hydrocarbons in the range of 7-12 carbons per molecule are the most sought after fractions in crude oil because they eventually become gasoline. Other hydrocarbons such as kerosene or jet fuel (C14H30) and diesel (C16H34) are also valuable products of refining because like gasoline they are fuels used in transportation. The most common reaction that these hydrocarbons undergo is combustion. When sufficient amounts of oxygen are available, the combustion of hydrocarbons is complete resulting in the production of carbon dioxide and water vapour. The general form of the equation is: a hydrocarbon + oxygen gas carbon dioxide + water vapour or A typical example is the combustion of propane: propane + oxygen carbon dioxide + water vapour or Page 43 of 88 When the amount of oxygen available is insufficient, the combustion is incomplete and poisonous carbon monoxide gas is produced. In this course, you can assume that hydrocarbon combustion is complete. What do you notice about the number of moles of oxygen required for complete versus incomplete combustion of propane in the equations above? Cracking and Reforming About 90% of the crude oil that enters a refinery exits as gasoline, furnace oil, and jet fuel. The other 10% or so is converted to hydrocarbons like ethene and styrene - starting materials used in the plastics industry. styrene However, the composition of crude oil is not proportional to the substances that are derived from it. Crude oil is not 90% C8H18, C14H30, and C16H34 and 10% C2H4 and C8H8. Crude oil contains hydrocarbons that vary from one to 30 or so carbon atoms per molecule. Since certain hydrocarbons are in greater demand than others, oil refineries use special processes to convert less valuable hydrocarbons into more valuable ones. Two of the most important processes used for this purpose are cracking and reforming. Cracking involves converting large alkanes to smaller alkanes, alkenes, and hydrogen. Two important types of cracking are thermal cracking and catalytic cracking. Thermal cracking involves heating large hydrocarbons in the absence of air until the carbon to carbon bonds break. Catalytic involves a the use of heat and a special chemical substance called a catalyst to break the bonds. Page 44 of 88 Polymers One of the best analogies for a polymer is the average train. A train consists of many individual cars joined together at the ends. A polymer is a huge molecule that is formed when hundreds or thousands of small molecules called monomers are bonded together. Polymers are literally everywhere. Paper is mainly a natural polymer called cellulose. Cotton, wool, and protein are other examples of natural polymers. The plastic your cell phone is polystyrene - a synthetic polymer. Synthetic polymers are so common now that you probably can’t imagine a world without them. Just think of it - no plastic bags, pipes or containers, no modern carpeting, no high-tech polishes and waxes - the list is extensive. About half of all synthetic polymers are the products of addition polymerization reactions. Natural polymers and the remainder of the synthetic polymers are formed by condensation polymerization . Page 45 of 88 Organic Halides: An organic halide is a compound that contains one or more halogen atoms as part of its molecular structure. Organic halides have many important uses including: fire retardation anaesthesia plastics manufacturing refrigeration/cooling systems The term alkyl halide is often used to represent organic halides derived from hydrocarbons. The general formula of an alkyl halide is R-X where R represents an alkyl group and X represents a halogen substituent. Naming Alkyl Halides Naming alkyl halides is a lot like naming branched alkanes. Here are the steps to follow: Identify and name the longest continuous chain of carbon atoms. Identify and name the halogen substituent(s). Assign lowest possible numbers to the substituents. 3. List the substituents in alphabetical order using appropriate prefixes. 4. Write the full name of the compound beginning with the names of the substituents and ending with the name of the parent. 1. 2. Example 1 Provide a IUPAC name for each structural formula. Page 46 of 88 a. b. c. Answer a. The parent is propane. It has chlorine substituents at carbons #1 and #3. The name of the structure is 1,3-dichloropropane. b. The parent is ethane. In alphabetical order, the substituents are two chlorine atoms at carbon #1 and two fluorine atoms at carbon #2. The name is 1,1,dichloro-2,2-difluoroethane. c. The parent is butane. The substituent is bromine. It is located at carbon #1 (the lowest possible number). The name is 1-bromobutane. Notice that in each example, the name of the halogen has been shortened and the letter o has been added. For example, chlorine atoms are represented by the substituent name chloro. Writing Structural Formulas for Alkyl Halides The approach to writing structural formulas for alkyl halides is much the same as writing structural formulas for branched aliphatics. Draw the parent chain Add a symbol for each halogen atom based on the information on its position in the name. Example 2 Write a structural formula for 1-chloro-1,2-difluoroethane. Answer Begin by drawing the parent; then, add the halogen substituents. Page 47 of 88 Organic Reactions: Two important reactions that result in the formation of organic halides are substitution and addition reactions. The essential difference between these reaction types is the type of hydrocarbons involved. Alkanes and benzene tend to undergo substitution while alkenes and alkynes tend to undergo addition. Production of Organic Halides: Substitution Reactions A substitution reaction occurs when a hydrogen atom is removed from the hydrocarbon and replaced by a halide substituent. The products are a hydrocarbon derivative and a hydrogen halide. A key point to remember about substitution reactions is that a hydrogen atom has to be removed from the hydrocarbon before a substituent can be added. Example 3 A substitution reaction. The example shows a substitution reaction involving methane and bromine. The product is bromomethane. When a bromine molecule absorbs energy, the covalent bond is broken resulting in the formation of bromine atoms. These atoms are good examples of radicals - very unstable and highly reactive particles. One of the bromine atoms removes a hydrogen atom to form hydrogen bromide while the other one bonds to the carbon from which hydrogen was removed. The reaction can be summarized by this equation. A question you might have at this point is: “Can more than one hydrogen atom be substituted?” That is a good question. The answer is yes. All four of the hydrogen atoms Page 48 of 88 in methane can be replaced by bromine atoms. How many bromine molecules would be needed to achieve this? The answer is four bromine molecules. It is possible to substitute four bromine atoms for hydrogen atoms in methane. For each step in the substitution reaction: a bromine molecule absorbs energy (e.g. light) and splits into two bromine atoms. one bromine atom removes a hydrogen atom to make HBr. and the other bromine atom replaces the hydrogen being removed. Example 4 Structural isomerism is the existence of two or more structural formulas for one chemical formula. Single step or multi-step substitution reactions can result in the production of structural isomers. Consider the reaction between propane and chlorine. If a hydrogen on carbon #1 is replaced, then the product is 1-chloropropane; however, if a carbon #2 hydrogen is replaced, then the product is 2-chloropropane. Is 3-chloropropane a third possibility? Substitution: Two-Stage Reactions Page 49 of 88 If a propane molecule reacts with two chlorine molecules, then there are several possible isomeric products! Example 5 Draw and name the structural formulas for possible isomeric products of a reaction between propane and two molecules of chlorine. Answer Stage 1: The first chlorine molecule reacts with propane. The products of the first step of the reaction are 1-chloropropane or 2-chloropropane. Stage 2a: If the second chlorine molecule reacts with 1-chloropropane; then the possible isomers are: 1,1-dichloropropane, 1,2-dichloropropane, and 1,3dichloropropane. Page 50 of 88 Stage 2b: If the second chlorine molecule reacts with 2-chloropropane; then the possible isomers are: 1,2-dichloropropane and 2,2-dichloropropane. Thus there are four different isomeric products possible for this two step substitution reaction. As you can imagine, a higher ratio of chlorine to propane results in even higher numbers of possible isomers. Production of Organic Halides: Addition Reactions Alkenes and alkynes are unsaturated hydrocarbons containing at least one double or triple bond respectively. They do not undergo substitution reactions; instead, they undergo addition - a reaction in which substituents are added to both carbons involved in the multiple bond. Alkenes and alkynes are chemically more reactive than alkanes because of the presence of the multiple carbon to carbon bonds. . The halogen atoms are added at the location of the double bonded carbon atoms. The reaction is spontaneous unlike substitution reactions which require light energy to break the covalent bonds in the diatomic halogen molecules. Addition Reactions In addition reactions, no hydrogen atoms are removed from the hydrocarbon. Substituents are bonded to the hydrocarbon using the bonding electrons that make up the multiple bond. In alkenes, a double bond is reduced to a single bond and in alkynes, a triple bond is reduced to either a double or a single bond depending on the amount of the substituent available for addition. Example 6 Page 51 of 88 Predict the products of addition reactions involving: a. ethene and chlorine. b. 1-butene and bromine. c. cyclohexene and fluorine. Answers a. The product is 1,2-dichloroethane. b. c. The product is 1,2-difluorocyclohexane Example 7 Predict the products of addition reactions between: a. one molecule of ethyne and one molecule of chlorine b. one molecule of ethyne and two molecules of chlorine Answer a. b. Page 52 of 88 Alkenes and alkynes also undergo addition reactions with a hydrogen halides. Markovnikov's Rule Markovnikov's rule (1870) This is an empirical rule based on Markovnikov's experimental observations on the addition of hydrogen halides to alkenes. The rule states that : "when an unsymmetrical alkene reacts with a hydrogen halide to give an alkyl halide, the hydrogen adds to the carbon of the alkene that has the greater number of hydrogen substituents, and the halogen to the carbon of the alkene with the fewer number of hydrogen substituents" This is illustrated by the following example: Look at the position of the H and the Br in relation to the statement of Markovnikovs rule given above. Example 8 Predict the product of a reaction between ethene and hydrogen chloride. Answer The covalent bond between hydrogen and chlorine is broken and these atoms are added to the double bonded carbon atoms. The product is chloroethane - a saturated alkyl halide. Important Points About Addition Reactions substituents are added to the multiple-bonded carbon atoms. Page 53 of 88 only one product is formed. alkenes undergo a one-stage addition alkynes may undergo either a one-stage or two-stage addition (if excess halogen is available). An Application of the Addition Reaction The decolourization of bromine water is an important test for the presence of a double carbon to carbon bond. This test is used to determine the level of unsaturation in vegetable oils and other substances that possess double bonds. The reaction is spontaneous. Bromine, which has a characteristic bright orange colour does not react as easily with saturated hydrocarbons. Elimination Reactions Halogen substituents can be removed from an alkyl halide in a reaction involving a base. The organic product of an elimination reaction is an unsaturated hydrocarbon. Example 9 Write a chemical equation to show the conversion of 2-chlorobutane to an unsaturated hydrocarbon. Answer Hydroxide ions (OH-) give a substance the properties of a base (e.g. high pH). In this elimination reaction, it removes a hydrogen from either carbon #1 or carbon #3. If a hydrogen is removed from carbon #1, then 1-butene is produced. If a hydrogen is removed from carbon #3, then 2-butene is produced. Page 54 of 88 The hydroxide ion combines with the hydrogen to produce water, and the eliminated chlorine atom becomes a chloride ion. Addition Polymerization Halide substituted alkenes will undergo addition polymerization. For example, common polyvinyl chloride plastic is the product of the addition polymerization of vinyl chloride (CH2CHCl) or chloroethene. Another common alkyl halide polymer is Teflon. It is the product of addition polymerization of 1,1,2,2-tetrafluoroethene. One pair of electrons in the double bond of each monomer is redistributed allowing the monomers to be joined by a single covalent bond. The joining of thousands of monomers produces a polymer strand. A typical Teflon coating of a frying pan consists of uncountable Teflon polymer molecules. Benzene In the lesson on aromatic hydrocarbons, you read about the special carbon to carbon bonds in the benzene ring. One piece of evidence cited to support the theory of delocalized bonding electrons was the chemical behaviour of benzene. Benzene behaves chemically like an alkane (a saturated compound) and not like the alkenes and alkynes (unsaturated compounds.) This is because the hybrid carbon to carbon bonds of the benzene ring are very stable and are not easily broken like the double bonds in alkenes and triple bonds in alkynes. Since the hybrid bond is not easily broken, reactions between halogens and benzene result in the substitution of hydrogen with halogen atoms. In other words, benzene behaves chemically like a saturated compound because it undergoes substitution reactions. Example 10 Write an equation using structural formulas to illustrate a reaction between: a. benzene and chlorine Page 55 of 88 b. one benzene molecule and two chlorine molecules Answer a. b. Are there other possible isomeric products in item b? Summary Remember that alkanes and benzene undergo substitution reactions while alkenes and alkynes undergo addition reactions. You must be able to identify the type of reaction (addition or substitution) that a given hydrocarbon will undergo, and draw the structural formulas of the organic reactants and products. If you are given a reaction equation with one reactant missing, you have to be able to determine the name and structure of the missing reactant. The first step is to determine the type of reaction that is occurring, then you work backwards to find the reactants. To distinguish between equations for addition and substitution reactions, look at the products. Substitution reactions produce an organic product and hydrogen or a hydrogen halide whereas addition reactions produce a single organic product. 1. Complete these equations for substitution reactions by providing the names and structural formulas of the products. If more than one isomeric product is possible, then draw structural formulas for at least two of the isomers. a. butane + fluorine hydrogen fluoride + ? Page 56 of 88 b. pentane + iodine c. d. hydrogen iodide + ? + 2 Br2 + 2 Cl2 2 HBr + ? 2 HCl + ? 2. Write an equation (using structural formulas for organic compounds) for the addition reaction involving each pair of substances: a. b. c. d. ethene and hydrogen iodide 1-pentene and chlorine cyclopentene and iodine propyne and excess chlorine 3. Write an equation (using structural formulas for organic compounds) for the elimination reaction involving each pair of substances: a. chloroethane and hydroxide ion b. iodopropane and hydroxide ion 5. Write an equation to illustrate the addition polymerization of 1-choropropene. 5. Write equations to illustrate the reactions between each pair of compounds. In cases where more than one isomeric product is possible, provide structural formulas and names for at least two isomers. a. benzene and fluorine b. fluorobenezene and chlorine c. benzene and two molecules of iodine Alcohols and Ethers: We tend to organize things by classifying them on the basis of observable features or properties. In other words, a class is defined by the properties that its members have in common. A set of common properties distinguishes one class from another. Hydrocarbon derivatives are defined on the basis of their functional groups - atoms or groups of atoms that give compounds their unique chemical and physical properties. Page 57 of 88 Alcohols are defined by the functional group called hydroxyl (-OH). The general formula for an alcohol is R-OH where R represents an alkyl group. Ethers are defined by the functional group known as ether (-O-). The general formula for an ether is R-O-R' where R and R' represent alkyl groups. In an ether, the alkyl groups can be the same or different. In the above example, the alkyl groups are methyls (-CH3). Naming and Drawing Structural Formulas for Alcohols What do the names methanol, ethanol and 1-propanol have in common? It should be pretty obvious - they all end in -ol. The -ol suffix in a chemical name identifies a compound as an alcohol; in other words, it signals the presence of a hydroxyl group. When you are given a structural formula that contains the hydroxyl group, follow these steps to name the compound: 1. Count to find the number of carbon atoms in the longest continuous chain (the alkyl stem). 2. Name the continuous chain of carbons in the same way you would name a corresponding alkane. 3. Change the -e ending of the alkane name to -ol. 4. Indicate the location of the hydroxyl group using the lowest possible number. Attach the number to the name with a hyphen. (Alcohols containing one or two carbon atoms have only one possible location for the hydroxyl group, so the position number can be omitted in those cases.) 5. If the alkyl group is branched, priority in the numbering of the parent goes to the location of the hydroxyl group. Naming Alcohols Example 1 Write the IUPAC names that correspond to these structural formulas. Page 58 of 88 a. b. c. d. Answers a. The longest chain is four carbons long, so the structure is derived from butane. The location of the hydroxyl group has to be assigned the lowest possible number - in this case the hydroxyl group is located on carbon #1. The name of the compound is 1-butanol. b. The longest chain is four carbons long, so the structure is derived from butane. There is a hydroxyl group located on carbon #2 (lowest possible number), so the name of the compound is 2-butanol. c. The longest chain is five carbons long, so the structure is derived from pentane. There is a hydroxyl group located on carbon #2, so the name of the compound is 2-pentanol. d. The longest chain is five carbons long, so the structure is derived from pentane. The carbon atom to which hydroxyl is bonded is designated as carbon #1 (the lowest possible number) which makes the carbon to which the methyl group is attached carbon #4. The name of the compound is 4-methyl-1-pentanol. Page 59 of 88 Structural Formulas for Alcohols To draw a structural formula when you are given the name of an alcohol, 1. draw a chain of one or more carbons based on the name of the alkyl parent; 2. then situate the hydroxyl group (and any other groups) based on the assigned number(s) in the name. Example 2 Draw a structural formula for each alcohol. a. 2-propanol b. 3-pentanol c. 2-methyl-2-butanol Answer a. First you draw the structure that corresponds to the alkyl prefix prop. Then, based on the number in the name 2-propanol, you add the hydroxyl group to carbon #2. or CH3CHOHCH3 b. Draw the structure that corresponds to the the alkyl prefix pent. Then add the hydroxyl group to carbon #3. or CH3CH2CHOHCH2CH3 c. Draw the structure for 2-methylbutane. Page 60 of 88 Add the hydroxyl group to carbon #2 of the parent chain. or CH3COH(CH3)CH2CH3 Alcohols: Two Special Cases Compounds that possess more than one hydroxyl group are called polyalcohols. An example is a radiator antifreeze, commonly known as ethylene glycol. Its systematic or IUPAC name is 1,2-enthanediol. See if you can use your nomenclature skills to draw its structural formula. 1,2-ethanediol Decompose the name from right to left. diol means two hydroxyl groups ethane means two single bonded carbon atoms 1,2 means the hydroxyl groups are located at carbons 1 and 2 Phenol is an alcohol in which the hydroxyl group is a substituent of a benzene ring. The name consists of the root of the word phenyl (which is used to identify benzene rings) and the suffix ol which represents a hydroxyl group. Page 61 of 88 Naming and Drawing Structural Formulas for Ethers Ethers are hydrocarbon derivatives that contain an oxygen atom bonded to two alkyl groups. They have the general formula of R-O-R' where R and R' are alkyl groups. The alkyl groups can be either the same or different. When you are given the structural formula for an ether, determine whether the alkyl groups are the same or different. if they are different, name and list them in alphabetical order as one word, and add the word ether to make a phrase. If they are the same, add the prefix di- to the alkyl name, and then write the word ether to complete the phrase. Example 3 Provide a IUPAC name for each ether. a. b. c. Answers a. The alkyl groups are propyl and ethyl. When written together in alphabetical order, they become ethylpropyl. Adding the word ether gives the full IUPAC name ethylpropyl ether. b. The alkyl groups are ethyl and methyl. This gives the alkyl name ethylmethyl. Adding the word ether gives the full name: ethylmethyl ether. c. Both alkyl groups are ethyl. The prefix di is used to make the alkyl component of the name: diethyl. The word ether is added to give the full name diethyl ether. Page 62 of 88 To draw the structural formula of an ether, draw the oxygen atom symbol and attach the alkyl groups to it. Example 4 Draw a structural formula for each ether. a. dimethyl ether b. butylmethyl ether Answers a. b. Reactions of Alcohols... Addition Reactions Addition reactions are an alternative to fermentation as a means of producing alcohols. These reactions proceed in much the same way as the addition reactions that produce alkyl halides except that water is added at the location of the double bond. Consider this example: The water molecule splits into hydrogen and a hydroxyl. These species are added to ethene at the location of the double bond. The product is ethanol. This reaction is an important synthetic source of ethanol. 1,2-ethandiol, commonly known as ethylene glycol or radiator antifreeze, can be produced by reacting ethyne with water: Page 63 of 88 Two water molecules are added at the location of the multiple bond. Is there another possible isomer in this reaction? 1,1-ethanediol If the hydroxyl groups are both located on the same carbon, then this structural isomer is possible. Elimination Reactions Alkenes can be produced by elimination of a water molecule from an alcohol. This reaction involves the use of an acid catalyst. A catalyst is a substance that speeds up a chemical reaction without being consumed. The acid catalyst in the example below is represented by the symbol H+. Can you see why this reaction is classified as elimination? It should be obvious that a hydroxyl group and a hydrogen atom are being eliminated from the alkyl parent. The result is the formation of an unsaturated hydrocarbon and water. An important application of this reaction type is the ripening of fruit in warehouses. The ripening process is stimulated when a plant produces ethene. If unripened fruit is stored under the right conditions, the production of ethene is inhibited allowing for long term storage. In order to initiate the ripening process, the fruit has to be exposed to ethene. This is where an elimination reaction involving ethanol becomes important. Properties of Alcohols and Ethers The properties of alcohols are a function of the hydrogen bonding associated with the highly polar "OH" bond. Page 64 of 88 Short chain alcohols like methanol, ethanol, and propanols have the unique property of being soluble in nonpolar and polar solvents. This makes them very useful for cleaning oily, greasy, or waxy materials. The alkyl component of these alcohols dissolves in nonpolar oils, grease, or wax while the hydroxyl end dissolves easily in water. The higher melting and boiling points of alcohols compared to corresponding aliphatic hydrocarbons is due to the strong hydrogen bonds that form between alcohol molecules and the slightly greater London dispersion forces due to the higher number of electrons per molecule. For example, ethane boils at -88.5°C whereas ethanol boils at 78.5°C. The properties of ethers are a function of the stable ether link between the alkyl groups. Aside from being highly flammable, ethers are generally unreactive. Ethers are volatile they evaporate more easily than alcohols because they lack hydrogen bonding. This property makes them useful as propellants (in spray cans), and solvents for varnishes and lacquers. Ethers have lower melting and boiling points than their alcohol isomers because they lack hydrogen bonding. Practice Items Exercise 1 Provide a IUPAC name for each structural formula. a. b. c. Page 65 of 88 d. e. f. Exercise 2 Draw structural formulas for the following alcohols. a. b. c. d. e. f. 2-methyl-2-pentanol 4-heptanol 2,2-dichloroethanol 8-ethyl-1-decanol 3-pentanol 2-octanol Exercise 3 Write balanced chemical equations for the following reactions. Provide structural formulas for all organic reactants and products. If more than one isomeric product is possible, draw at least two structural formulas for the possible isomers. a. b. c. d. 2-propene reacts with water 2-pentene reacts with water water is eliminated from 2-butanol water is eliminated from 1-pentanol Exercise 4 Page 66 of 88 Provide the name and structural formula for an alcohol which can be used to produce the given product. a. 1-butene b. 2-pentene Exercise 5 Provide the name and structural formula for and alkene that can undergo an addition reaction with water to produce the given alcohol. a. 2-hexanol b. 3-heptanol Exercise 6 Name these ethers. a. b. c. Exercise 7 Draw structural formulas for the following ethers. a. b. c. d. ethylmethyl ether diethyl ether dimethyl ether butylethyl ether Exercise 8 Draw structural formulas for and name all the possible alcohol and ether isomers of C4H10O. Page 67 of 88 Aldehydes and ketones: Aldehydes and ketones are two more groups of hydrocarbon derivatives. What do they have in common? How are they different? How can they be distinguished from each other. Aldehydes and ketones both contain the functional group carbonyl (-C=O). The carbonyl group consists of a carbon atom and an oxygen atom joined together by a double bond. The location of the carbonyl group in a carbon chain determines whether the hydrocarbon derivative is an aldehyde or a ketone. A functional group gives a compound its unique chemical and physical properties. Based on this definition, you would think that aldehydes and ketones have similar properties. Aldehydes: Aldehydes have a terminal carbonyl group - that is, the carbonyl group is located at the end of the molecule. A good way to remember this fact is that the name aldehyde begins with "al" and the word terminal ends in "al". The general formula of an aldehyde is R–CHO where R represents a single hydrogen atom or a chain of carbon atoms (usually an alkyl group). Page 68 of 88 The simplest aldehyde is methanal, H2CO. The carbon of the carbonyl group is the only carbon atom in the molecule. How many carbon atoms should an ethanal molecule possess? Naming Aldehydes To name an aldehyde from a structural formula: 1. Identify the longest continuous chain of carbon atoms (including the carbon atom in the carbonyl group). 2. Write the name of the corresponding alkane and replace the -e ending of the alkane name with -al. Note that the carbon of the carbonyl group is counted as part of the carbon chain for naming purposes. Example 1 Provide a name for each structural formula. a. b. Answers a. Since there are three carbon atoms in the carbon chain, you need to start with the name propane. Change the -e ending in propane to -al to get the name propanal. Notice that there is no need to indicate the position of the carbonyl group in an aldehyde because it is always attached to a terminal carbon atom (i.e. carbon #1). b. There are five carbon atoms in a continuous chain, but there is also a methyl group. The numbering of the carbon chain begins with the carbon in the Page 69 of 88 carbonyl group. Therefore, the methyl group is located at carbon #4. The name is 4-methylpentanal. Structural Formulas of Aldehydes Drawing structural formulas for aldehydes involves determining the number of carbon atoms in the carbon chain, adding any alkyl groups listed in the name, and drawing a double bond to an oxygen atom on the terminal carbon. Example 2 Provide structural formulas for these aldehydes. a. heptanal b. 2-methylbutanal Answers a. The heptan- portion of the name suggests seven single bonded carbon atoms. The -al ending indicates the presence of a terminal carbonyl group. b. The 2-methylbutan- portion of the name suggests a chain of four carbons with a methyl group at carbon #2. The -al ending indicates the presence of a terminal carbonyl group. Page 70 of 88 Notice that the carbonyl carbon is designated as carbon #1 - this is a very important point! Ketones: Ketones also contain the functional group called carbonyl; however, unlike the aldehydes, the carbonyl group in ketones is located on a non-terminal carbon. This means the simplest possible ketone is propanone: CH3COCH3. The general formula for ketones is R–CO–R', where R and R' represent alkyl groups. The carbon of the carbonyl group is counted as part of the carbon chain for naming purposes. The shortest carbon chain in a ketone is three carbons in length. Naming Ketones To name a ketone from a structural formula: 1. Identify the longest continuous chain of carbon atoms (including the carbon atom in the carbonyl group). 2. Write the name of the corresponding alkane and replace the -e ending of the alkane name with -one. 3. If the carbon chain is five carbon atoms or longer, indicate the position of the carbonyl group by assigning it the lowest number possible. Example 3 Provide names for these ketones. a. Page 71 of 88 b. Answers a. The carbon chain is six carbons long so it corresponds to the alkane name hexane. Convert the alkane name to hexanone. The carbonyl group carbon is assigned the lowest possible number - in this case #3. Thus the name is 3hexanone. b. The carbon chain is five carbon atoms long which corresponds to the name pentane. The carbonyl group is on carbon #3. There is a methyl group at carbon #2 (the lowest possible number it can be assigned). The name is 2-methyl-3pentanone. Structural Formulas for Ketones Writing structural formulas for ketones follows a similar sequence of steps to those used for aldehydes above. Determine the number of carbon atoms in the carbon chain from the alkane component of the name. Locate the carbonyl group from the number that precedes the alkane part of the name. Draw in any alkyl groups that precede the ketone name. Example 4 Provide structural formulas for these ketones. a. butanone b. 3-ethyl-4-methyl-2-hexanone Answers a. Begin by drawing the carbon chain. Page 72 of 88 Add a double bonded oxygen atom to a non-terminal carbon. b. Draw the chain of six carbons. Add an ethyl group to carbon #3 and a methyl group to carbon #4. Add a double bonded oxygen to carbon #2. Some Properties and Uses of Aldehydes and Ketones Many aldehydes and ketones have pleasant odours. For example, benzaldehyde gives almonds their distinctive flavour while cinnamaldehyde gives the aroma associated with oil of cinnamon. These compounds, like many other aldehydes and ketones, occur in nature but they may also be synthesized in a lab from alcohols. Methanal (commonly known as formaldehyde) is by far the most common aldehyde. As formalin (a 40% solution of methanal and water), it is used as a tissue preservative in biology and hospital laboratories and as embalming fluid in funeral homes. Page 73 of 88 Perhaps the most widely recognized ketone is propanone (commonly known as acetone). It is found in substances such as nail polish remover, varnish, and liquid cleaners. Propanone, like some alcohols, dissolves polar and nonpolar solutes and is commonly used as a cleaner in organic chemistry laboratories. Isomerism How many possible structures are there for the molecular formula C 3H6O? The answer is several. Of the possible structures, how many are aldehydes and/or ketones? Most aldehyde compounds with three or more carbon atoms per molecule have a ketone isomer. Practice Items Exercise 1 Provide a IUPAC name for each aldehyde or ketone. a. b. c. d. Page 74 of 88 Exercise 2 Provide a structural formula for each aldehyde or ketone. a. b. c. d. 3-methylbutanal octanal 2-heptanone 4,4-dimethyl-2-pentanone Exercise 3 Draw structural formulas for and name three isomers of C4H8O. Page 75 of 88 Carboxylic Acids Organic acids are common. The one you are probably the most familiar with is ethanoic acid which is also known as acetic acid or simply vinegar (a 5% by volume solution of aqueous acetic acid). You have probably heard of the term fatty acids as well. Fatty acids are long chain hydrocarbons that have a carboxyl group at one end. They are found in animal fats and vegetable oils. C17H35COOH Carboxylic Acids The functional group that gives organic acids, also known as carboxylic acids, their chemical and physical properties is the carboxyl group, -COOH. You can think of a carboxyl group as a carbonyl group and a hydroxyl group rolled into one. + = The general formula for the carboxylic acids is RCOOH where R represents a hydrogen atom or alkyl group. Unlike carbonyl and hydroxyl groups, carboxyl groups are always terminal. The carbon atom of the carboxyl group is considered to be part of the alkyl stem. Naming Carboxylic Acids To name a carboxylic acid when given a structural formula: 1. name the longest continuous chain of carbons, including the carbon of the carboxyl group, using an alkane name. The carbon atom in the carboxyl group is carbon #1. 2. if present, list the names of any alkyl branches and assign each a number. Build the name as you would for a branched hydrocarbon. 3. replace the -e ending of the hydrocarbon name with the suffix -oic. 4. add the word acid to the first name to make a phrase. Page 76 of 88 Example 1 Provide a IUPAC name for each structural formula. a. b. Answers a. Including the carbon of the carboxyl group, the carbon chain is three carbon atoms long, so the root of the name is propane. There are no alkyl groups. Change the -e ending to -oic to get propanoic. Add the word acid to get the name propanoic acid. b. The longest continuous chain of carbon is five atoms long, so the root of the name is pentane. There is an ethyl group at the third carbon from the carboxyl group, so the alkyl component of the name becomes 3-ethylpentane. Replace the -e ending with -oic, and add the word acid to the name: 3-ethylpentanoic acid Structural Formulas for Carboxylic Acids To draw the structural formula for a carboxylic acid, 1. draw the main carbon chain. 2. attach any alkyl groups listed in the name. 3. situate a carboxyl group at the end of the carbon chain. Example 2 Draw a structural formula for each carboxylic acid. a. butanoic acid b. 2-methylbutanoic acid Page 77 of 88 Answers a. Draw a chain of four carbon atoms: Convert carbon #1 to a carboxyl group: . b. Draw a chain of four carbon atoms: Add a methyl group to carbon #2: Convert carbon #1 to a carboxyl group: Esters Esters are abundant in nature. Many of the pleasant odours you associate with flowers and berries are due to esters as are the scents of bath oils, shampoos, soaps, and room fresheners, etc. Esters are soluble in oils but not water. In the heyday of the whaling industry, whale blubber was boiled down to make the oils in which esters from plants were dissolved. Esters are relatively easy to synthesize in a lab. Nowadays, when you see the phrase "artificially flavoured" on the packaging of your favourite snack or candy, chances are that the flavour is due to a synthesized ester. The functional group of an ester is actually a combination of a carbonyl group from an organic acid and an ether link from an alcohol. Page 78 of 88 Esters are produced by reacting carboxylic acids with alcohols. The general formula of an ester is RCOOR' where R represents hydrogen or a carbon chain/alkyl group and R' represents an alkyl group. Naming Esters To name an ester from a structural formula: 1. Count to find the number of carbon atoms in the -OR' component of the structural formula (the part derived from an alcohol) and assign it an alkyl group name. 2. Count the number of carbon atoms in the R-C=O component of the structural formula (the part derived from the carboxylic acid) and assign it an alkane name with an -oate ending in place of the -oic ending. 3. combine the names to make a phrase. Example 3 Provide a IUPAC name for each structural formula. a. b. Answers a. The -OR component of the molecule is propyl. The R-C=O component is derived from propanoic acid so its name is propanoate. The two names are combined to give propyl propanoate. b. The -OR component of the molecule is methyl. The R-C=O component is derived from butanoic acid so its name is butanoate. The two names are combined to give methyl butanoate. Page 79 of 88 Structural Formulas for Esters To draw a structural formula of an ester from a name, 1. draw carbon chains using the alkyl prefixes from the name and join them using an ether bridge. 2. add a double bonded oxygen to carbon #1 of the carboxylic acid component of the structure. Example 4 Provide a structural formula for each ester. a. butyl ethanoate b. phenyl ethanoate Answers a. Draw an ether link between an ethyl group and a butyl group: Add a double bonded oxygen atom to the component derived from carboxyl: b. Draw an ether link between an phenyl group and a ethyl group: Add a double bonded oxygen atom to the component derived from carboxyl: Page 80 of 88 Esterification Esters are often classified as derivatives of carboxylic acids. Esters are produced when alcohols and carboxylic acids are reacted in the presence of an acid catalyst. Practice Items Exercise 1 Provide a IUPAC name for each structural formula. a. b. c. Exercise 2 Provide a structural formula for each carboxylic acid a. heptanoic acid b. ethanoic acid c. 2-methylpentanoic acid Page 81 of 88 Exercise 3 Provide a IUAPC name for each ester. a. b. c. Exercise 4 Provide a structural formula for each ester. a. b. c. d. e. f. methyl ethanoate heptyl propanoate ethyl ethanoate propyl methanoate butyl methanoate ethyl octanoate Exercise 5 Draw structural formulas for and name the carboxylic and ester isomers for each molecular formula. a. C3H6O2 b. C4H8O2 Page 82 of 88 Exercise 6 Complete each equation by providing the IUPAC name of the acid and the alcohol (in that order) from which the given ester is produced. a. + b. + c. methyl methanoate + propyl ethanoate Amines and Amides: You might recall that esters tend to have pleasant scents. Well, the same cannot be said for amines and amides. Their scents are characteristically unpleasant. Urea is one of many common examples. Amines Amines are derived from ammonia (NH3) when more of the hydrogen atoms are replaced by a hydrocarbon group. A nitrogen atom is the functional group. In this course, you will focus on primary amines or those that consist of one hydrocarbon group bonded to an amino group (-NH2). These amines have the general formula RNH2 where R represents an alkyl group. To name an amine, identify the alkyl group and add the suffix -amine to its name. Example 1 Provide a name this structural formula. Answer The alkyl group consists of four carbon atoms, so its name is butyl. It is bonded to an amino group, so its name is butylamine. Page 83 of 88 To draw a structural formula for an amine, determine the length of the carbon chain from the alkyl name and add an amino group to a terminal carbon. Example 2 Provide a structural formula for ethylamine. Answer Draw an ethyl group: Add the amino group: Amides The functional group of an amide consists of a carbonyl group and an amino group. An amide can be produced by reacting a carboxylic acid with ammonia (NH3). The general formula for amides is RCONR'R'', where R, R', and R'' represent alkyl groups or hydrogen. However, in this course, we will restrict discussion of amides to the general formula RCONH2 where R represents hydrogen or an alkyl group. To name an amide, write the name for the carbon chain containing the carbonyl group, drop the -e ending, and add the suffix -amide. Page 84 of 88 Example 3 Provide a name for this structural formula. Answer The carbonyl group is part of a four carbon chain. This gives the root name butane. Dropping the -e ending in butane and add the suffix -amide, you get butanamide. To draw a structural formula for a simple amide, determine the length of the carbon chain from the alkyl prefix in the name, and add a double bonded oxygen and an amino group (NH2) to carbon #1. Example 4 Write a structural formula for propanamide. Answer Draw the carbon chain first and then add a double bonded oxygen and an amino to carbon #1 Amino Acids Amino acids are the building blocks of proteins. Proteins are the stuff of life! See if you can identify the amino and the carboxylic acid components in this structural formula. Page 85 of 88 Practice Items Exercise 1 Provide a name for each structural formula. a. b. c. d. Exercise 2 Provide a structural formula for each compound. a. ethanamide b. pentylamine Polymers Polymers are huge molecules that form when small molecules called monomers are joined together. Polymers can be natural or synthetic. Natural polymers originate in living things. Examples include starch, protein and cellulose. Even the matter that makes up your genetic code (DNA) is a polymer. Synthetic polymers are things like Dacron®, Teflon®, nylon, polyvinyl chloride (PVC), polyethylene, polypropylene and polystyrene. The list is quite extensive! Page 86 of 88 Condensation Polymerization The term condensation usually means a phase change from the gas state to the liquid state; however, in organic chemistry, it also describes a type of chemical reaction in which a by-product molecule is formed as two molecules are joined together. Esters and amides are produced by condensation reactions. A condensation polymer is the product of condensation chain reaction. With each monomer that becomes part of the polymer, a by-product molecule is produced. unlike addition polymers which can only grow at one end, a condensation polymer can grow in two or more directions at once. Here are some examples of molecules involved in condensation polymerization reactions: What do these molecules have in common? How do they differ from molecules that undergo addition polymerization? Monomers are molecules that are chemically combined at the location of their functional groups. Your MHR Chemistry text presents two examples of condensation polymerization on page 428 and 429. Review those examples before viewing the animation in Example 2. Did you notice that some polymerization reactions involve two different monomers? Proteins may contain many different monomers (amino acids) - see page 438 of your MHR Chemistry text. Page 87 of 88 Page 88 of 88