Download Chapter23

Chapter 23 Functional Groups
23.1 Introduction to Functional Groups - In this section, you will learn how functional groups determine the "character"
and reactions of organic compounds.
1. Functional Groups
There are hundreds of different types of organic chemistry reactions, yet hydrocarbon skeletons are generally inert.
The myriad of organic reactions are caused by a an array of substituents called functional groups.
A functional group is a specific arrangement of atoms in an organic compound that is capable of characteristic chemical
reactions.
Organic compounds can be classified according to their functional groups. The table below shows the functional
groups that affect a compounds reactivity.
The symbol R represents any carbon chain or ring attached to the functional group. Double and triple bonds of alkenes
and alkynes affect reactivity and are also considered to be functional groups, but are not listed in the table.
Like the table above, Reference table R shows the main functional groups of organic chemistry.
2. Halogen Substituents - A halocarbon is a carbon-containing compound with a halogen substituent.
Halocarbons are a class of organic compounds containing covalently bonded fluorine, chlorine, bromine, or iodine.
These are named just like other hydrocarbons with alkyl or substituent groups.
Ex.
Ex. Draw 2,2-dibromopentane
Some common halocarbons are shown below - IUPAC name is given and the common name is in parenthesis.
Very few halocarbons are found in nature, but they can be readily prepared. 2-bromo-2-chloro-1,1,1-triflouroethane is
used in car air conditioning systems.
As any halocarbon becomes more substituted with halogens, the boiling point of the substance increases. This is due
an increase in molecular mass, which increases the strength of the intermolecular forces. Consider the table below.
3. Substitution Reactions - A common type of organic reaction is a substitution reaction, in which an atom, or a group
of atoms, replaces another atom or group of atoms.
A halogen can replace a hydrogen atom on an alkane to produce a halocarbon. The general equation is below
Most organic reactions proceed slowly because relatively strong covalent bonds must be broken first. Most reactions
therefore, require a catalyst.
Example of a common substitution reaction is below. Ultraviolet light is the catalyst.
Treating benzene with a halogen in the presence of a catalyst causes the substitution of a hydrogen atom in the ring.
Halocarbons can be treated with a base (hydroxide ions) to form an alcohol. The X represents the halogen.
Example
Section Review
1. How are organic compounds classified?
2. What is a halocarbon?
3. How can a halocarbon be prepared?
4. Identify the functional group in each structure: CH3OH, CH3CH2NH2, C6H5COOH, CH3CH2CH2Br, CH3CH2OCH2CH3
5. Write the structure of
2-choropropane
1-iodo-2,2-dimethylpentane
23.2 Alcohols and Ethers
1. Alcohols - An alcohol is an organic compound with an — OH group.
The —OH functional group in alcohols is called a hydroxyl group. Table R shows R-OH, where R is any hydrocarbon.
In order to name an alcohol, the position of the hydroxyl group is indicated by a number before the name. The
hydrocarbon must be numbered so that the position of the OH group is the lowest possible number.
When naming an alcohol, drop the -e ending of the parent hydrocarbon name and add the ending -ol. For instance,
Sample Problems
Write the structural formula for: 2-methyl-2-propanol
and
3-pentanol
Alcohols can have more than one hydroxyl group to form diols and triols (system of naming is the same)
2. Properties of Alcohols - Alcohols are capable of hydrogen bonding because they contain the "OH" hydroxyl group.
Alcohol Boiling points - Hydrogen Bonding causes alcohols to boil at higher temperature than alkanes and halocarbons
with the same # of carbon atoms. Ex. Ethanol b.p. = 79oC at 101.3 kPa, while ethane = -89oC
Alcohol Solubility - Alcohols of up to four carbons are soluble in water in all proportions. The solubility of alcohols with
four or more carbons in the chain is usually much lower, because the molecule as a whole is more nonpolar.
3. Production of Ethanol (CH3CH2OH) - Fermentation is the production of ethanol from sugars by the action of yeast or
bacteria.
Ethanol is the intoxicating substance in alcoholic beverages. It is a depressant that can be fatal if taken in large doses
at once.
Denatured alcohol is ethanol with an added substance (CH4OH or wood alcohol) to make it toxic (poisonous).
4. Addition Reactions - Addition reactions of alkenes are an important method of introducing new functional groups
into organic molecules.
Double and triple bonds between carbon atoms are much more reactive than single bonds between carbon atoms.
In an addition reaction, a substance is added at the double or triple bond of an alkene or alkyne.
Ex. Addition across a double bond is signified by the following general equation
Ex.
Ex. The addition of water to an alkene forms an alcohol.
Ex. Double bonds can be halogenated by the addition of F2, Cl2, Br2, or I2 forming a disubstituted halocarbon.
Ex. The addition of hydrogen to a carbon-carbon double bond to produce an alkane.
5. Ethers (Table R) - An ether is a compound in which oxygen is bonded to two carbon groups (or R groups).
Ethers are typically volatile liquids. Diethyl Ether was used as an anesthetic for over a century.
The general structure of an ether is R—O—R'. The alkyl groups attached to the ether linkage are named in
alphabetical order and are followed by the word ether. Ex.
When the R group is the same on both sides, it is acceptable to drop the prefix di.
Ex.
Ethers have lower boiling points than alcohols of comparable mass. Ethers are less soluble than alcohols, but more
soluble than hydrocarbons and halocarbons (the O in the ether helps create some polarity).
Section Review
1. How are alcohols named?
2. How can functional groups be introduced into unsaturated hydrocarbon molecules?
3. Write the general structure for an ether and describe how they are named.
4. Write the structures of the following compounds
a. 2-butanol
b. 2-methyl-1-propanol
c. ethyl propyl ether
d. butyl propyl ether
5.
Write the product for the following addition rx
+
H-Br --------->
23.3 Carbonyl Compounds - In this section you will learn the structure, properties, and reactions of carbonyl
compounds.
1. Aldehydes and Ketones- Recall that alcohols have an O atom bonded to a carbon group (R) and a hydrogen. Ethers
have an oxygen bonded to two carbon groups.
An oxygen can be bonded to a single carbon atom by a double covalent bond. This is called on carbonyl group.
A carbonyl group is a functional group with the general structure C═O.
The C═O functional group is present in aldehydes and ketones. Table R
An aldehyde is an organic compound in which the carbon of the carbonyl group is always joined to at least one
hydrogen. Ex.
Naming Aldehydes
Aldehydes are named by replacing the "e" at the end of the name of the hydrocarbon and adding "al". The carbon chain
must be numbered so that the aldehyde functional group is at the lowest number. A number does not need to be given
to indicate the position of the aldehyde functional group because it is always at the end of the hydrocarbon. Ex.
3-methylbutanal
butanal
A ketone is an organic compound in which the carbon of the carbonyl group is joined to two other carbons (not an H).
Naming ketones
Ketones are named by changing the ending of the longest continuous carbon chain that contains the carbonyl group
from "e" to "one". If the hydrocarbon has more than 3 C atoms, the position of the C=O must be indicated. Ex.
propanone
2-hexanone
3-pentanone
If there are other substitent groups, the carbonyl chain is always numbered to give the carbonyl group the lowest
number. Ex. 3-ethyl-4-methy-2-hexanone
Properties of aldehydes and ketones
All small chain (3 carbons and less) are soluble in water because hydrogen bonding exists between the C=O and H
atoms of water. As the length of the chain increases, the compounds are less soluble.
They have lower boiling points than comparable alcohols and higher boiling points than comparable hydrocarbons.
Alcohols have stonger intermolecular forces (better hydrogen bonding, while hydrocarbon intermolecular forces are
weak).
Uses of Aldehydes and Ketones
They are isolated from plants and animals and have fragrent penetrating odors. Almonds contain benzaldehyde, vanillin,
and cinnimon all have flavors due to aldehydes and ketones. In addition, 2-propanone (called acetone) is an excellent
solvent used in nail polish remover.
The simplest aldehyde methanal (formaldehyde) is used for preserving biological specimens and is in embalming fluid;
however, it has been shown to cause cancer and is not used as frequently to preserve specimens.
2. Carboxylic Acids - are also called organic acids. They contain a carboxyl group
A carboxylic acid is a compound with a carboxyl group. A carboxyl group consists of a carbonyl group attached to a
hydroxyl group. Ex.
Like aldehydes, a carboxyl group (COOH) is always at the end of a hydrocarbon chain. So its position does not need to
be indicated when namings. All carboxylic acids are named by dropping the "e" from the end of the name of the
hydrocarbon and adding "oic" followed by the word acid.
Carboxylic Acids are abundant and widely distributed in nature. The low mass carboxylic acids are colorless volatile
liquids with sharp, unpleasant odors. High mass carboxylic acids are waxy, oderless solids with low melting points. The
table above lists the simplest organic acids.
Low mass carboxylic acids are soluble in water because the carboxyl group can form Hydrogen bonds with water.
The intermolecular forces among ethanoic acid molecules(main ingredient in store bought vinegar) are stronger than the
Hydrogen bonding of water, leading to ethanoic acid's higher boiling point (Table H).
3. Esters - Esters have very pleasant fruity odors and give blueberries, pinnaples, apples, pears, bannanas, and other
fruits their great taste and distinctive aromas. Flowers typically smell due to esters as well.
Esters are derivatives of carboxylic acids in which the —OH of the carboxyl group has been replaced by an —OR from an
alcohol.
Esters are named by naming the alkyl group from the alcohol, followed by the name of the orignial organic acid, but the
"ic acid" is replaced by "ate".
ex. propyl ethanoate (pear smell)
and
methyl ethanoate
The above examples are the two ways an ester could be written. The "oate" ending is always given to the carbon chain
containing the C=O.
Esterfication Reactions - The combination of a carboxylic acid and an alcohol form an ester.
Ex. The production of ethyl ethanoate from ethanoic acid and ethanol is a very common.
4. Triglyceriedes - Natural oils and fats exist as triesters of glycerol with fatty acids called triglycerides
Saponification reactions - Soap is prepared by the hydrolysis of triglycerides(animal fat) with a basic solution like
NaOH(aq).
Section Review questions
1. What is a carbonyl group?
2. What is the general formula of a carboxylic acids?
3. What is the general structure of an ester?
4. What is the reaction product of propanioic acid and 1-butanol? (esterfication reaction)
5. Draw the structure of:
3-pentanone
2-methylpropanal
23.4 Polymerization - In this section, you will learn some characteristics of monmers and polymers.
1. Addition Polymers
Up until this point, we have considered organic molecules of low molar mass, but some of the most important organic
molecules are giant molecules called polymers. You see polymers everyday. All plastics are polymers and so is the
miracle molecule DNA, which is responsible for nearly all the life forms on Earth and is currently controlling the activities
of every cell in your body.
A polymer is a large molecule formed by the covalent bonding of repeating smaller molecules. They can be natural
(DNA, protein, cellulose, etc.) or synthetic (PVC, nylon, mylar, kevlar, polyester, etc)
The smaller molecules that combine to form a polymer are called monomers. Some polymers are composed of one type
of monomer while others are composed of a combination of different monomers(copolymers).
An addition polymer forms when unsaturated monomers react to form a polymer.
a. Ex. Ethene ---> polyethylene (polymer name typically depends on the common names of their monomers)
**The double bond is converted into a sinle bond, while the other 2 electrons form carbon bonds on each side.**
Low Density Polyethylene (LDPE) makes up most clear "everday platics" like plastic bottles, bags, kitchen wrap, etc.
Long polyethylene chains have a degree of order. If the long chains are made more highly ordered by a catalyst or
extrusion, High Density Polyethylene (HDPE) forms, which has more rigidity and a higher tensile strenth than LDPE.
Tensile Strength - a measurement of the force applied to stretch a polymer until it breaks.
b. Ex. Polypropylene is a stiffer polymer than LDPE and is used extensively for utensils and containers.
c. Ex. Polystyrene forms a white rigid foam that is an excellent insulator of heat (coffee cups, insulation, etc.)
d. Polyvinyl chloride (PVC) is used for pipes in plumbing. It is also produced in sheets, sometimes with a fabric
backing, for use as a tough plastic upholstery covering.(see p. 748-749 for reactions).
e. Polytetrafluoroethene (Teflon™or PTFE) is the product of the polymerization of tetrafluoroethene monomers.
PTFE is very resistant to heat and chemical corrosion. (cookware , wire insulation, cables, motors, generators)
f. Polyisoprene, harvested from tropical plants such as a rubber tree, is the polymer that constitutes rubber.
(tires, rubber bands, soles of athletic shoes, and many other common items).
2. Condensation Polymers - Condensation polymers are formed by the head-to-tail joining of monomer units. These
monomer units must have two functional groups each. When the monmers link, water is typcially released.
Ex. Consider the formation of a type of polyester called PET.
3. Polymers with Amines and Amides (also condensation molecules)
Amines and Amides (See table R) are named accordingly with examples in the table. The R' and R" groups are Hydrogen.
Many important polymers are formed by the reaction of carboxylic acids (R-COOH) and amines (R-NH2)
Polyamides are polymers in which the carboxylic acid and amine monomer units are linked by amide bonds.
Common examples are polyamides are nylon, nomex, and kevlar.
Section Reveiw Questions
1. Describe how addition polymers form.
2. What is a polymer? What is a monomer?
3. How is water involved in the formation of condensation polymers?
4. Give names and uses of three types of polymers
5. What structure must a monomer have if it is to undergo addition polymerization?