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General Physical Science Organic Chemistry Organic Chemistry Scientists had originally thought that organic compounds contained a “vital force” due to their natural origin. This was disproved by Friedrich Wöhler in 1828. Wöhler was able to make urea, a carbon compound in human urine, in the laboratory from a mineral. Organic chemistry is the chemistry of carbon compounds Inorganic chemistry is the chemistry of compounds of all elements other than carbon. 2 Organic Chemistry The general properties of carbon compounds are: 1. Most carbon compounds are nonelectrolytes. 2. The reaction rates of carbon compounds are usually slow. 3. Many carbon compounds oxidize slowly in air but rapidly if heated. 4. Most carbon compounds are unstable at high temperatures. 3 Bonding in Organic Compounds Besides carbon, the most common elements in organic compounds are hydrogen, oxygen, nitrogen, sulfur, and the halogens. All of the preceding elements are non-metals, therefore organic compounds have covalent bonding. S H2 N2 O2 F2 Halogens Group 7A Cl2 I2 Br2 4 Numbers and Types of Bonds Application of the octet rule indicates that these elements should bond as shown below: Element Total Bonds C 4 N 3 O 2 H 1 5 Section 14.1 Example - Identifying Structural Formulas Two structural formulas are shown above. Which one does not represent a real compound? In structure (a) each H and halogen has one bond, each C has four bonds, and each O has two bonds. This is a valid structure. 6 Section 14.1 Example - Identifying Structural Formulas As we examine (b), we note that each H has one bond, each C has four bonds, the N has three bonds, BUT the O has three bonds. The O should only have two bonds. Therefore (b) is not a valid structure. 7 Section 14.1 Example 2 - Identifying Structural Formulas H3C O O CH3 C N N C C C N CH N CH3 The structural formula above appears in a recent chemistry book. Check the number of bonds to each atom and determine whether any bonding rules are violated. 8 Section 14.1 Example 2 - Identifying Structural Formulas O should have two bonds, C should have 4 bonds Each C should have 4 bonds H3C O CH3 C N N C C C O N CH N CH3 This is not a valid structure for caffeine! Each N should have 3 bonds 9 Section 14.1 Hydrocarbons Hydrocarbons are the most simple organic compounds. Hydrocarbons contain only carbon (C) and hydrogen. (H) For classification purposes, all other organic compounds are considered derivatives of hydrocarbons. Hydrocarbons can be divided into aromatic and aliphatic hydrocarbons. 10 Section 14.2 Classification of Hydrocarbons Hydrocarbons Aromatic Aliphatic Alkanes Cycloalkanes Alkenes Alkynes 11 Section 14.2 Aromatic Hydrocarbons Aromatic hydrocarbons contain one or more benzene ring. Benzene (C6H6) is the most important aromatic hydrocarbon. It is a clear, colorless liquid with a distinct odor, and is a carcinogen (cancer-causing agent.) Traditional Lewis Structure 12 Section 14.2 Benzene Structural Formulas and Short-hand Symbols The Lewis structure and the Kekulé symbol both indicate that the carbons in the ring have alternating double and single bonds. Benzene (Kekule symbol) Benzene (modern symbol) 13 Section 14.2 Benzene representation Benzene representation showing a flat molecule with six delocalized electrons forming a cloud above and below the plane of the ring. Properties of the benzene molecule and advanced bonding theory indicate this structure. The six electrons appear to be shared by all the carbon atoms in the ring. 14 Section 14.2 When Other Atoms are Substituted for the H’s in the Benzene Ring A vast array of other compounds can be produced CH3 O2 N NO2 NO2 TNT (2,4,6-trinitrotoluene) 15 Section 14.2 Example - Drawing Benzene Derivatives Draw the structural formula for 1,3-dibromobenzene. First, Draw a benzene ring. 16 Section 14.2 Example - Drawing Benzene Derivatives Second, attach a bromine atom (“bromo”) to the carbon atom at the ring position you choose to be number 1. Br 17 Section 14.2 Example - Drawing Benzene Derivatives Third, attach a second (“di”) bromine atom to ring position 3 (you may number either clockwise or counterclockwise from carbon 1) and you have the answer. 1,3-dibromobenzene Br Br 18 Section 14.2 Benzene Aromatic compounds naphthalene anthracene phenanthrene C10H8 C14H10 C14H10 chrysene C18H12 Aliphatic compounds are organic compounds that do not contain benzene rings. 19 Aliphatic Hydrocarbons Aliphatic hydrocarbons are hydrocarbons having no benzene rings. Aliphatic hydrocarbons can be divided into four major divisions: Alkanes Cycloalkanes Alkenes Alkynes 20 Section 14.3 Alkanes Alkanes are hydrocarbons that contain only single bonds. Alkanes are said to be saturated hydrocarbons Because their hydrogen content is at a maximum. Alkane general formula CnH2n + 2 The names of alkanes all end in “-ane.” Methane butane are gases Pentane C17H36 are liquids C18H38 and higher are solids 21 Section 14.3 Structural Formulas Alkanes or Hydrocarbons Methane 1 carbon Ethane CH4 2 carbons Propane 3 carbons Butane 4 carbons CH3 –CH2 –CH2 -CH3 Pentane 5 carbons Hexane 6 carbons Heptane 7 carbons Octane 9 carbons 22 The First Eight of the Alkane Series All satisfy the general formula CnH2n + 2 Name Molecular Formula Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10 Pentane C5H12 Hexane C6H14 Heptane C7H16 Octane C8H18 23 Section 14.3 Visualization of an Alkane’s Structure H H H–C–C–H H H CH3CH3 Structural formula – a graphical representation of the way atoms are connected Condensed structural formula – save time/space and are convenient Ball-and-Stick models – 3D models that can be built by students 24 Section 14.3 Models of Three Alkanes Names, Structural Formulas, Condensed Structural Formulas, and Ball-and-Stick Models Ethane H Full structural formula: H–C–C–H H Condensed structural formula: H H CH3CH3 Ball and Stick Model: 25 Section 14.3 Methane – Tetrahedral Geometry Ball-and-Stick & SpaceFilling Models Carbon’s four single bonds form angles of 109.5o H C H H H 26 Section 14.3 Alkanes – Energy Related Products Methane = primary component of natural gas Propane & Butane = primary component of bottled gas Gasoline = pentane to decane Kerosene = alkanes with n = 10 to 16 Alkanes with n > 16 diesel fuel, fuel oil, petroleum jelly, paraffin wax, lubricating oil, and asphalt 27 Section 14.3 Petroleum Products Fractional distillation C1 to C4 Gases 20oC C5 to C9 70oC C5 to C10 120oC C10 to C16 170oC C14 to C20 270oC C20 to C50 450oC 600oC Catalytic cracking Modern cracking uses zeolites as the catalyst. C20 to C70 >C70 28 Petroleum Products 42 gallons = 1 barrel Petroleum Asphalt Boiler oil Other Jet fuel 1.25 gal 1.3 gal 2.9 gal 4.2 gal 4.2 gal Diesel fuel 8.4 gal Gasoline 19.7 gal 29 Alkyl Group Alkyl group contains one less hydrogen than the corresponding alkane. In naming this group the “-ane” is dropped and “-yl” is added. For example, methane becomes methyl. Ethane becomes ethyl. 30 Section 14.3 Alkyl Group This group does not exist independently but occurs bonded to another atom or molecule. H H H–C–H H–C– H H Methane Methyl group CH3 31 Section 14.3 Constitutional Isomers Compounds that have the same molecular formula but different structural formulas In the case of many alkanes there is more than one way to arrange the atoms For example butane and isobutane Both of these alkanes have the molecular formula of C4H10 But their structural formula and arrangement is quite different 32 Section 14.3 Butane Continuous-Chain or Straight-Chain Structure H H H H H–C–C–C–C–H H H H C4H10 H 33 Section 14.3 Isobutane (2-methylpropane) Branched-chain Structure C4H10 34 Section 14.3 Constitutional Isomers Constitutional Isomers may exist whenever it is possible to construct a different structural arrangement: Using the same number and types of atoms Without violating the octet rule In other words, the same atoms may be connected to one another in different, but valid, ways. 35 Section 14.3 Number of Possible Isomers of Alkanes Carbon Atoms can bond in many different ways Name Molecular Formula Number of Isomers Methane CH4 1 Ethane C2H6 1 Propane C3H8 1 Butane C4H10 2 Pentane C5H12 3 Hexane C6H14 5 Heptane C7H16 9 Octane C8H18 18 C15H32 4,347 36 Section 14.3 IUPAC System of Nomenclature Compound is named as a derivative of the longest continuous chain of C atoms. Positions & names of the substituents added If necessary, substituents named alphabetically More than one of same type substituent – di, tri, tetra The C atoms on the main chain are numbered by counting from the end of the chain nearest the substituents. Each substituent must have a number. 37 Section 14.3 Example 5 4 3 2 1 CH3 – CH2 – CH2 – CH – CH3 CH3 The longest continuous chain of C atoms is five Therefore this compound is a pentane derivative with an attached methyl group Start numbering from end nearest the substituent The methyl group is in the #2 position The compound’s name is 2-methylpentane. 38 Section 14.3 Substituents in Organic Compounds Formula Name Br – Cl – F– I– CH3 – Bromo Chloro Fluoro Iodo Methyl 39 Section 14.3 Example - Drawing a Structure from a Name Draw the structural formula for 2,3-dimethylhexane. Note that the end name is hexane . Draw a continuous chain of six carbon (C) atoms, with four bonds around each. –C–C–C–C–C–C– 40 Section 14.3 Example - Drawing a Structure from a Name Number the C atoms from right to left. Attach a methyl group (CH3--) to carbon number 2 and number 3. Add necessary H atoms. 2,3-dimethylhexane –C–C–C–C–C–C– 6 5 4 3 2 1 41 Section 14.3 Cycloalkanes Members of the cycloalkane group possess rings of carbon atoms. They have the general formula CnH2n. Each carbon atom is bonded to a total of four carbon or hydrogen atoms. The smallest possible ring consists of cyclopropane, C3H6. 42 Section 14.3 The First Four Cycloalkanes Condensed Structural Formula Name Cyclopropane Cyclobutane Cyclopentane Cyclohexane Note that in the condensed structural formulas, there is a carbon atom at each corner and enough hydrogens are assumed to be attached to give a total of four single bonds. 43 Section 14.3 Alkenes Members of the alkene group have a double bond between two carbon atoms. One hydrogen atom has been removed from two adjacent carbon atoms, thereby allowing the two adjacent carbon atoms to form a double bond. General formula is CnH2n Begins with ethene (ethylene) C2H4 44 Section 14.3 Structural Formulas Functional Groups Alkenes Ethene 2 carbons Alkynes Ethyne 2 carbons Propene 3 carbons Propyne 3 carbons Butene Butyne 4 carbons 4 carbons Pentene 5 carbons Pentyne 5 carbons Hexene 6 carbons Hexyne 6 carbons Heptene 7 carbons Heptyne 7 carbons Octene Octyne 9 carbons 9 carbons 45 Some Members of the Alkene Series Name Molecular Formula Ethene C2H4 Propene C3H6 1-Butene C4H8 2-Butene C4H8 1-Pentene C5H10 46 Section 14.3 Naming Alkenes “-ane” suffix for the corresponding alkane is changed to “-ene” for alkenes. A number preceding the name indicates the C atom on which the double bond starts. The carbons are numbered such that the double bond has the lowest number. For example, 1-butene and 2-butene 47 Section 14.3 Alkenes Alkenes are very Reactive and are termed “unsaturated hydrocarbons” Alkenes will characteristically react with hydrogen to form the corresponding alkane. 48 Section 14.3 Unsaturated Hydrocarbons Unsaturated compounds have double or triple carbon-carbon bonds and are more reactive than saturated compounds Saturated compounds have only single carbon-carbon bonds (alkanes and similar compounds 49 Alkynes Members of the alkyne group have a triple bond between two carbon atoms. Two hydrogen atoms have been removed from each of two adjacent carbon atoms, thereby allowing the two adjacent carbon atoms to form a triple bond. General formula is CnH2n-2 Begins with ethyne (acetylene) C2H2 50 Section 14.3 Some Members of the Alkyne Series Name Molecular Formula Ethyne C2H2 Propyne C3H4 1-Butyne C4H6 2-Butyne C4H6 1-Pentyne C5H8 51 Section 14.3 Alkynes are Unsaturated Hydrocarbons Due to the triple carbon bond, each alkyne molecule can react with two molecules of hydrogen. 52 Section 14.3 Derivatives of Hydrocarbons Organic molecule characteristics depend on the number, arrangement, and type of atoms. Functional Group – any atom, group of atoms, or organization of bonds that determine specific properties of a molecule Generally the functional group is the reactive part of the molecule. Due to the functional group’s presence, certain predictable properties ensue. 53 Section 14.4 Alkyl Halides Alkyl halides have the general formula R—X, where X is a halogen and R is an alkyl group CFC’s (chlorofluorocarbons) are examples of alkyl halides. A well known CFC is dichlorodifluoromethane (Freon-12) Extensively used in the past in cooling devices. Destroys Ozone layer which protects us from UV rays 54 Section 14.4 Example - Drawing Constitutional Isomers Draw the structural formulas for the two alkyl halide isomers that have the molecular formula C2H4Cl2. Recall that C atoms form four bonds, H & Cl form one bond each. Draw a two-carbon backbone. Add enough bonds so that each C has four. 55 Section 14.4 Example - Drawing Constitutional Isomers Note, there are just enough open bonds to attach the four H and two Cl atoms. Fill in the Cl atoms in as many ways as possible. Remember that you are constrained by the tetrahedral geometry (109.5o) of the four C bonds. • Fill in the open bonds with H atoms and name the compounds. 56 Section 14.4 Alcohols Alcohols are organic compounds containing the hydroxyl group, —OH, attached to an alkyl group. General formula is R—OH Their IUPAC (International Union of Pure and Applied Chemistry) names end in “-ol.” The most simple alcohol is methanol Also called methyl alcohol or wood alcohol. (poisonous) 57 Section 14.4 Alcohols Another common alcohol is ethanol. (CH3CH2OH) Also known as ethyl alcohol or grain alcohol Least toxic and most important of the alcohols Ethanol is used in alcoholic beverages, perfumes, dyes, and varnishes. 58 Section 14.4 Other Alcohol Examples Rubbing alcohol is another alcohol example. Also known as 2hydroxypropane or isopropyl alcohol Ethylene glycol is an alcohol used widely as an antifreeze and coolant. 59 Section 14.4 Structural Formulas Functional Groups Alcohols Ethanol 2 carbons Propanol 3 carbons Butanol 4 carbons Pentanol 5 carbons Hexanole 6 carbons Heptanol 7 carbons Octanol 9 carbons 60 Carbohydrates Compounds that contain multiple hydroxyl groups in their molecular structure. Names end in “-ose” Sugars, starches, and cellulose are the most important carbohydrates. Glucose (C6H12O6) and fructose (C6H12O6) are important sugars. Note that glucose and fructose are isomers. 61 Section 14.4 Carbohydrates - Sugars Fructose is the sweetest of all sugars and is found in fruits and honey. Glucose (also called dextrose) is found in sweet fruits, such as grapes and figs, in flowers, and in honey. Carbohydrates must be broken down into glucose for circulation in the blood. 62 Section 14.4 Carbohydrates - Starch Starch consists of very long chains (up to 3000 units) of glucose. Produced by plants in their seeds, tubers, and fruits When these plants parts are eaten, our digestive processes covert the starches back into glucose. 63 Section 14.4 Amines Organic compounds that contain nitrogen and are basic (alkaline) are called amines. General formula for an amine is R—NH2. One or two additional alkyl groups could be attached to the N atom, in place of H atoms. Most simple amines have strong odors. Odor from raw fish Amine examples include methylamine, dimethylamine, and trimethylamine. 64 Section 14.4 Carboxylic Acids Carboxylic acids contain the carboxyl group . (–COOH) They have the general formula RCOOH. 65 Section 14.4 Carboxylic Acids Formic acid is the simplest carboxylic acid. This is the substance that causes the painful sting of insect bites. • Vinegar is a 5% solution of acetic acid. 66 Section 14.4 Esters Ester – a compound that has the following general formula RCOOR’ In the general formula for an ester the R and R’ can be any alkyl group. • Although R and R’ can be identical, they are usually different. Contrary to amines, most esters have pleasant odors. • Many flowers and ripe fruits have fragrances and tastes due to one or more esters. 67 Section 14.4 Fats Fats are a type of ester formed by the combination of the trialcohol named glycerol and fatty acids. Glycerol is CH2(OH)CH(OH)CH2(OH) Stearic Acid (C17H35COOH) is found in beef fat, and is a typical fatty acid. 68 Section 14.4 Fats Generally fats from animals are solid at room temperature. Fats from plants and fish are generally liquid at room temperature. Liquid fats are referred to as oils. 69 Section 14.4 Soap – Like Dissolves Like Soap – the sodium salts of fatty acids Generally we want to dissolve stains made by nonpolar compounds such as grease. The polar end of the soap dissolves in water. The other end of the soap molecule is long and nonpolar. This nonpolar end dissolves in the grease. The emulsified grease droplets can be rinsed away. 70 Section 14.4 Amides Amides are nitrogen-containing organic compounds with the general formula RCONHR’. 71 Section 14.4 Amide Formation Amide formation is similar to ester formation. A carboxylic acid reacts with an amine to form water and an amide, as shown below. 72 Section 14.4 Amino Acid Amino acids are organic compounds that contain both an amino and carboxyl group. Glycine and alanine are the simplest amino acids. Proteins are extremely long polyamides, formed by the condensation of amino acids. Proteins can range from a few thousand formula units (insulin) to several million formula units. Proteins serve as both structural components and enzymes. 73 Section 14.4 Synthetics Attempts to duplicate nature have long been a goal of chemists. Basic formulas and structures became known as the science of chemistry progressed. As attempts were made to synthesize natural compounds, synthetic compounds were created. Synthetics are materials whose molecules have no duplicate in nature. 74 Section 14.5 Synthetic Polymers Due to the scientific approach, chemists were able to tailor new molecules for specific purposes. Plastics are probably the best known of this group of synthetic polymers. They can be molded and hardened for many different purposes. 75 Section 14.5 Synthetic Polymers A polymer is a compound of very high formula mass whose long chain molecules are made of repeating units. Monomer is the fundamental repeating unit of a polymer. There are two major types of polymers: Addition polymers Condensation polymers 76 Section 14.5 Addition Polymers Addition polymers are formed when molecules of an alkene monomer add to one another. Recall that alkenes have a double bond between two carbon atoms. Under the proper reaction conditions the double bond opens up and attaches itself by single bonds to two other monomer molecules. Each of these monomers will then in turn attach to another monomer, and so on and on… 77 Section 14.5 Polymerization of Ethene The subscripted n on polyethylene indicates that the unit shown in brackets is repeated thousands of times. Polyethylene is the simplest of the synthetic polymers. It is significantly inert chemically and is used to make containers. 78 Section 14.5 Polymerization Polymerization-the making of plastics Vinyl 79 Teflon Teflon is made by the polymerization of tetrafluoroethene. This polymer is a hard, strong, chemically resistant compound with a high melting point and very low surface friction. 80 Section 14.5 Example - Drawing an Addition Polymer An addition polymer can be prepared from vinylidene chloride, CH2==CCl2. Draw the structure of the polymer. To form the polymer the double bonds of all the monomers (CH2==CCl2) must open up and repeatedly bond to the growing chain of monomers. The structure is shown as: 81 Section 14.5 Condensation Polymers Condensation polymers are formed from molecules of two or more reactive groups. Water is the other product, hence the name condensation polymers. Polyethylene terephthalate (PET) is formed from the polymerization of tetephthalic acid and ethylene glycol. 82 Section 14.5 Nylon – A Condensation Polymer Nylon was first introduced to the public in 1939 at the New York World’s Fair. Nylon is formed from the polymerization of adipic acid and hexamethylenediamine. 83 Section 14.5 Velcro Velcro is a popular fastener made of nylon. The hooks of one surface entangle the loops of the other surface. The inventor noticed how cockleburrs clung to his clothing. 84 Section 14.5