Q.An organic compound (A) with molecular formula C₂H₅Cl reacts with KOH to give compound (B), and with alcoholic KOH gives compound (C). Identify (A), (B) and (C).

Because the C(delta+)-X(delta-) bond makes the carbon electron-poor, a wide range of nucleophiles displace X- there, each giving a distinct functional group -- this table of named substitutions is tested heavily. Aqueous KOH or moist Ag2O/H2O gives an alcohol (hydrolysis). Alcoholic ammonia gives a primary amine, but with EXCESS haloalkane the amine keeps reacting further (ethylamine -> diethylamine -> triethylamine -> a quaternary ammonium salt) -- ammonolysis. Alcoholic KCN gives an alkyl cyanide/nitrile (attack through carbon), while alcoholic AgCN instead gives the alkyl isocyanide (attack through nitrogen) -- cyanide is an 'ambident nucleophile', with two different atoms able to bond, and which one attacks depends on whether the metal (K, soft/ionic vs Ag, forms a more covalent, nitrogen-first bond) favours the softer carbon end or the harder nitrogen end. The same ambident idea repeats with the nitrite ion: sodium/potassium nitrite gives an alkyl nitrite ester (O-attack, R-O-N=O), while silver nitrite instead gives a nitroalkane (N-attack, R-NO2). Sodium/potassium hydrogen sulphide gives a thiol. Sodium al …