A hydrocarbon 'P' ($C_4{H}_8$) on reaction with $HCl$ gives an optically active compound 'Q' ($C_4{H}_{9}Cl$) which on reaction with one mole of ammonia gives compound 'R' ($C_4{H}_{11}N$). 'R' on diazotization followed by hydrolysis gives 'S'. Identify P, Q, R and S.