benzene to diphenyl :

in presence of  benzene forms bromobenzene then undergoes fittig raction to form diphenyl  and 2NaBr.

aniline to chlorobenzene :

on diazotisation in the presence of   at  temperature 273-278K it forms benzenediazonium chloride and then undergoes sandmeyer reacion to form chlorobenzene.

ethylchloride to propanoic acid :

on addition of KCN nucleophilic substiution takes place and propanenitrile is formed which on hydrolysis forms propanoic acid.

2-methyl-1-propene to 2-chloro2-methyl-propane :

on addition of HCl it undergoes Markonikoff's addition reaction to form the desired product.

2chlorobutane to 3,4dimethylhexane:

2-chlorobutane + 2Na ----->(in the presence of dry ether,it undergoes wurtz reaction) 3,4-dimethlyhexane

ethanol to propanenitrile :

ethanol ----> forms iodoethane 

on addition of  KCN nucleophilic substitution takes place to form propanenitrile