Organic compounds predominantly consist of Carbon and Hydrogen atoms, also known as hydrocarbons. However, most organic compounds also contain other heteroatoms like O, N, S, and halogens as the functional group.
Out of the many ways to classify a structure, the functional group classification based on the attached atoms is listed below.
Classification of functional groups
- Functional groups with only C and H atoms
- Functional groups with Halogen atoms
- Functional groups with the Oxygen atoms
- Functional groups with the Nitrogen atom
- Functional groups that are carboxylic acid derivatives
- Functional Groups with other heteroatoms
1) Functional Groups with only C and H- Aliphatic, Alicyclic, and aromatic hydrocarbons
The carbon and hydrogens containing hydrocarbons are classified as aliphatic, alicyclic, and aromatic compounds.
Aliphatic compounds have carbons connected in straight and branched chains. The carbons chain is bonded like a closed ring in alicyclic and aromatic compounds. Alicyclic compounds have only single bonds, whereas aromatic compounds have alternating single and double bonds, making them essentially planar.
The compounds with only single bonds between the carbon atoms are called saturated hydrocarbons (alkanes). In contrast, the carbon with double and triple bonds is called unsaturated hydrocarbons (alkenes and alkynes).
Aromatic hydrocarbons are mostly benzene derivatives. They have alternating single and double bonds; however, the double bonds are not localized but delocalized on the ring. The aromatic hydrocarbons are planar and have special stability known as resonance stability.
R, R1, R2, R3- indicates Alkyl group
Ar-stands for Aryl group
2) Functional groups with Halogen atoms
The Halogen-substituted alkanes, alkenes, and arenes consist of alkyl halides and the aryl halides functional group.
X- indicates the Halogen atoms.
3) Functional groups with O atoms
Oxygen is the next abundant heteroatom in organic chemistry after the Carbon and Hydrogen atoms. Many of the functional groups containing the oxygen atoms are-
4) Functional groups with Nitrogen atom
Functional Groups containing Nitrogen are – amines, nitriles, and nitro compounds.
5) Functional groups that are carboxylic acid derivatives
The functional groups derived from carboxylic acids (R-COOH) have the OH part replaced with OR (for ester functional group), NH2 (for amide), OCOR (for anhydride), and Cl (for acid chloride).
6) Functional Groups with other heteroatoms
Some functional groups contain other heteroatoms like S, P that have Sulfur (S) and Phosphorus (P). Their examples are-