Question
Base strength of
$$\eqalign{
& \left( {\text{i}} \right)\,{H_3}C\mathop C\limits^\Theta \,{H_2} \cr
& \left( {{\text{ii}}} \right)\,{H_2}C = \mathop C\limits^\Theta H \cr
& \left( {{\text{iii}}} \right)H - C \equiv \mathop C\limits^\Theta \cr} $$
is in the order of
A.
(ii) > (i) > (iii)
B.
(iii) > (ii) > (i)
C.
(i) > (iii) > (ii)
D.
(i) > (ii) > (iii)
Answer :
(i) > (ii) > (iii)
Solution :
Weaker the acid, stronger is its conjugate base. Among alkane, alkene and alkyne, alkynes are most acidic and alkanes are least acidic, so the order of base strength is
$$\eqalign{
& alkane > alkene > \,alkyne\,\,\,\,\,\,{\text{or}} \cr
& C{H_3}\mathop C\limits^\Theta {H_2} > {H_2}C = \mathop C\limits^\Theta H > H - C \equiv \mathop C\limits^\Theta \cr} $$