Overview

Functional groups are groups of atoms with specific chemical properties that occur within organic molecules and are sometimes denoted as “R”. Functional groups can “functionalize” a compound by enabling it to adopt different physical and chemical properties.

Types of Advanced Functional Groups

The table below summarizes some of the major functional groups in organic chemistry.

Class of Organic Compounds Skeletal Structures of Compounds with Functional Groups in Red Names of Compounds
Aromatic hydrocarbon Figure1 Benzene
Phenol Figure2 Phenol (Hydroxybenzene)
Aldehyde Figure3 Ethanal (Acetaldehyde)
Ketone Figure4 Acetone
Acid or acyl chloride Figure5 Acetyl chloride
Carboxylic acid Figure6 Ethanoic acid (Acetic acid)
Ester Figure7 Ethyl acetate
Amine Figure8 Ethylamine
Amide Figure9 Acetamide
Nitrile Figure10 Acetonitrile
Phosphate Figure11 Methyl dihydrogen phosphate

This text is adapted from  Openstax, Chemistry 2e, Section 20.2: Alcohols and Ethers and Section 20.3: Aldehydes, Ketones, Carboxylic Acids, and Esters.

Procedure

Functional groups are atoms or groups of atoms within an organic compound that impart distinctive chemical properties.  

One of the important functional groups in organic chemistry is the carbonyl functional group, composed of a carbon atom double-bonded to oxygen.

Two closely related carbonyl-based organic compounds are aldehydes and ketones. In aldehydes, the carbonyl carbon is bonded to an alkyl group and a hydrogen atom. The exception is formaldehyde, in which the carbonyl carbon is bonded to two hydrogens.

Meanwhile, in ketones, the carbonyl carbon atom is bonded to two other carbon atoms within a hydrocarbon skeleton.

The carbonyl group forms a part of many larger functional groups, such as the carboxyl group of carboxylic acids, which is composed of a hydroxyl group bound to the carbonyl carbon.

Functional derivatives of carboxylic acids include esters, in which the hydrogen of the carboxyl group is replaced by an alkyl group; amides, in which the OH of the carboxyl group is replaced by an amine; and acyl chlorides, in which the OH is replaced by a chloride.

Multiple bonds are a feature of other functional groups, such as the nitrile or cyano functional group, with a carbon atom triple-bonded to nitrogen.

Benzene is an aromatic hydrocarbon that is often represented as six carbon atoms in a ring with alternating single and double bonds. Benzene minus one hydrogen serves as phenyl—a functional group. A hydroxyl group attached to the phenyl-based aromatic ring forms a phenol.

An amine is a non‑carbon-containing functional group defined by an electronegative nitrogen atom with a lone pair of electrons singly bonded in a hydrocarbon framework. They are classified as primary, secondary, and tertiary, depending on the number of carbon atoms bonded to nitrogen.

Likewise, a phosphate functional group has a phosphorus atom covalently bonded to four oxygen atoms. Up to three hydrocarbon chains can be attached to the oxygen atoms singly bonded to the phosphorus to obtain organophosphates.