Retrosynthesis is a process that involves the breakdown or formation of bonds of an available starting molecule to reach the required compound.

1. Retrosynthesis for forming benzoic acid from benzene

• Oxidation of ethylbenzene gives benzoic acid.
• Ethyl benzene can be formed by the Friedel-Craft alkylation of benzene.

1. Retrosynthesis for forming aniline from benzene

• \({\rm{N}}{{\rm{H}}_{\rm{2}}}\)group cannot be directly substituted to benzene; it can be formed by the reduction of the nitro group.
• Nitro group can be introduced by nitration using a strong acid.

1. Retrosynthesis for forming 2-bromo benzoic acid from benzene

• Oxidation of ethylbenzene gives an acid group.
• Bromine is an ortho, para-directing group. It can be introduced by the bromination of toluene.
• Acylation of benzene gives toluene.