Which carbocation would be most stable?
A)I
B)II
C)III
D)IV

Question

Which carbocation would be most stable? 
A)I 
B)II 
C)III 
D)IV

Quizplus · Accepted Answer

Carbocation stability is directly proportional to the number of alkyl groups attached to the positively charged carbon. In carbocation I, there are no alkyl groups attached to the positively charged carbon. In carbocation II, there is one alkyl group attached to the positively charged carbon. In carbocation III, there are two alkyl groups attached to the positively charged carbon. In carbocation IV, there are three alkyl groups attached to the positively charged carbon but one of them is a methyl group which is smaller than an ethyl group. In carbocation V, all three alkyl groups are ethyl groups but the positive charge is attached to a terminal carbon which is less stable than the central carbon. Therefore, carbocation III is the most stable due to having two ethyl groups attached to the positively charged carbon.

Which Carbocation Would Be Most Stable