The carbonyl group. A carbonyl group consists of a carbon atom bonded to an oxygen atom through a double bond. Aldehydes and ketones are compounds that contain a carbonyl functional group. The carbonyl carbon in an aldehyde has at least one hydrogen attached to it, and the carbonyl carbon in a ketone has no hydrogens.

Nomenclature of aldehydes and ketones. The IUPAC names of aldehydes and ketones are based on the longest carbon chain that contains the carbonyl group. The chain numbering is done from the end that results in the lowest number for the carbonyl group. The names of aldehydes end in -al, those of ketones in -one.

Physical properties of aldehydes and ketones. The boiling points of aldehydes and ketones are intermediate between those of alcohols and alkanes. The polarity of the carbonyl groups enables aldehyde and ketone molecules to interact with each other through dipole - dipole interactions. They cannot, however, hydrogen-bond to each other. Lower-molecular-mass aldehydes and ketones are soluble in water.

Reactions of aldehydes and ketones. Oxidation of primary and secondary alcohols, using mild oxidizing agents, produces aldehydes and ketones, respectively. Aldehydes are easily oxidized to carboxylic acids; ketones do not readily undergo oxidation. Reduction of aldehydes and ketones produces primary and secondary alcohols, respectively.

Hemiacetals, hemiketals, acetals, and ketals. A characteristic reaction of aldehydes and ketones is the addition of an alcohol across the carbonyl double bond to produce hemiacetals and hemiketals. The reaction of a second alcohol molecule with a hemiacetal or hemiketal produces an acetal or a ketal.

The carboxyl group. The functional group present in carboxylic acids is the carboxyl group. A carboxyl group is composed of a hydroxyl group bonded to a carbonyl carbon atom. It thus contains two oxygen atoms directly bonded to the same carbon atom.

Nomenclature of carboxylic acids. The IUPAC name for a monocarboxylic acid is formed by replacing the final -e of the hydrocarbon parent name with -oic acid. The longest carbon chain containing the functional group is identified, and it is numbered starting with the carboxyl carbon atom. Common-name usage is more prevalent for carboxylic acids than for any other type of organic compound.

Physical properties of carboxylic acids. Low-molecular-mass carboxylic acids are liquids at room temperature and have sharp or unpleasant odors. Long-chain acids are wax-like solids. The carboxyl group is polar and forms hydrogen bonds to other carboxyl groups or other molecules. Thus carboxylic acids have relatively high boiling points, and those with lower molecular masses are soluble in water.

Acidity of carboxylic acids. Soluble carboxylic acids behave as weak acids, donating protons to water molecules. The portion of the acid molecule left after proton loss is called a carboxylate ion.

Reactions of carboxylic acids. Carboxylic acids are neutralized by bases to produce carboxylic acid salts. Such salts are usually more soluble in water than are the acids themselves. Carboxylic acid salts are named by changing the -ic ending of the acid to -ate. Carboxylic acids react with alcohols to produce esters.

Esters. Esters are formed by the reaction of an acid with an alcohol. In such reactions, the - OR group from the alcohol replaces the - OH group in the carboxylic acid. Esters are polar compounds, but they cannot form hydrogen bonds to each other. Therefore, their boiling points are lower than those of alcohols and acids of similar molecular mass.

Nomenclature of esters. An ester is named as an alkyl (from the name of the alcohol reactant) carboxylate (from the name of the acid reactant).

Hydrolysis of esters. In ester hydrolysis, the bond between the carbonyl carbon atom and the oxygen is broken, and free acid and free alcohol are produced.

Classification of amides. An amide is derived from a carboxylic acid by replacing the hydroxyl group with an amino or a substituted amino group. Amides, like amines, can be classified as primary, secondary, or tertiary, depending on how many nonhydrogen atoms are attached to the nitrogen atom.

Amides. The nomenclature for amides is derived from that for carboxylic acids by changing the -oic acid ending to ?amide. Groups attached to the nitrogen atom of the amide are included as prefixes, using a capital N- with each group to indicate location.

Properties of amides. Amides do not exhibit basic properties in solution. The electronegative oxygen atom in the carbonyl group draws electron density away from the nitrogen, leaving very little electron density on the nitrogen to bond to an incoming proton. Most unbranched amides are solids at room temperature and have correspondingly high boiling points because of strong hydrogen bonds between molecules.

Hydrolysis of amides. In amide hydrolysis, the bond between the carbonyl carbon atom and the nitrogen is broken, and free acid and free amine (or ammonia) are produced.

Condensation polymers. A condensation polymer is formed by the reaction of difunctional monomers to give a polymer and some small molecule. Polyesters, made using diacid and dialcohol monomers, contain ester linkages between monomers. Polyamides, made using diacid and diamine monomers, contain amide linkages between monomers.