Question

What are the funtional group that are usefull for the extention of carbon chain?

Answer 1

Notable functional groups include:

Functional groups containing oxygen:
hydroxyl -OH,
carbonyl >C =O
carboxyl -COOH
alkoxy -OR (Type-OCH3)

Functional groups containing unsaturatedcarbon-carbon bonds:
double and triple bonds (including conjugated dienesystem) -C=C-, -C≡C-
aromatic moieties, С₆H₅, etc.

Functional groups containing other atoms:
metal atoms-Li
halogen atoms-Cl, etc.