Chemistry, Third edition

340 18 · COMMON CLASSES OF ORGANIC COMPOUNDS

Derivatives of carboxylic acids

Esters are one family of compounds that can be derived from carboxylic acids. These

and some other derivatives are shown below:

All these derivatives contain the acylgroup or RCO– O

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R—C—

the acyl group

BOX 18.3

Some examples of carboxylic acid derivatives

Nylon

The man-made fibre nylon 6,6 is an example of a polymer that consists of long-chain

molecules, containing repeating –CONH–groups. Its formula is

OO OO

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····C(CH 2 ) 4 C—NH(CH 2 ) 6 NH—C(CH 2 ) 4 C—NH(CH 2 ) 6 NH·····

The–CONH–group is also present in amides:

Nylon is therefore a polyamide. Proteins are also examples of polyamides.

Nylon 6,6 chains are formed by the reaction of many hexanedioic acid molecules with hexan-

1,6-diamine molecules (a member of the amine family). Molecules of water are produced so

that the chains can form. The formation of long chain molecules from two different monomers,

with elimination of water, is called a condensation polymerizationreaction:

wheren= a large number.

Fats and oils

These are naturally occurring esters of the triol glycerol (propan-1,2,3-triol). A fat is a substance

that is solid at room temperature, whereas an oil is liquid. In vegetable oils, the hydrocarbon

chains have many double bonds (they are polyunsaturated). Fats, however, tend to have very

few, or no double bonds. Removal of most of the double bonds in a vegetable oil, by reaction

with hydrogen (hardening), will convert it to a solid fat. Hardened corn oil, for example, is used

to make margarine.

Hydrolysis of these fats or oils gives glycerol and fatty acids as products.