Carbonyl groups are also present in carboxylic acids, esters and amides. However, in these compounds, the carbonyl group is only part of the functional group. Carboxylic acid is an organic compound with a carboxyl group. The carboxyl group is a functional group containing a carbon-oxygen double bond. There is also an OH group attached to the same carbon atom, but it has its own characteristic properties. Like aldehydes and ketones, the writing formula of carboxylic acid can clearly show the carbon-oxygen double bond, or the carboxyl group can be written on a line in a concentrated form. Generally speaking, carboxylic acids are represented by the formula RCOOH, where R is a hydrocarbon group. The primary amines of diamines and polyamines can be called diamines or triamines when their amino groups are attached to an open-chain hydroxyl group or directly attached to a benzene ring. More complex amines can be named as derivatives of hydrocarbons. Quaternary amine compounds can be named as amine derivatives.
The ester is represented by the formula RCOOR', where R and R'are hydrocarbyl groups. Esters are organic compounds derived from carboxylic acids and alcohols, in which the OH of the acid is replaced by the OR group, which looks a bit like an ether and a bit like a carboxylic acid. Even so, this group of compounds react neither like carboxylic acids nor ethers; they form a unique family. Unlike ethers, esters have a carbonyl group. And unlike carboxylic acids, esters have no acidic hydrogen atoms; they have a hydrocarbon group instead.
Amine is a compound derived from ammonia (NH3); it has one, two or all three NH3 hydrogen atoms replaced by an alkyl group (or an aryl group). Like NH3, amines are weak bases. The amine functional group is a nitrogen atom with a pair of lonely electrons, with one, two or three alkyl or aryl groups attached. The amide functional group has a carbonyl group attached to a nitrogen atom from ammonia or amine.
The properties of amide functional groups are different from those of simple carbonyl groups, NH3 and amines.