The cyclic cations having the same number of hyperconjugation are : Choose the correct answer from the options given below :
- B and C Only
- A and B Only
- A and C Only
- A, C and D Only
Answer
(3) A and C Only
Solution
Number of hyperconjugation structures of a carbocation = number of α-hydrogens (C–H bonds on the carbons directly attached to C ).
A: C is attached to CH3 (3 H), a ring CH2 (2 H) and the ring CH carrying the ethyl group (1 H)
α-H = 3 + 2 + 1 = 6
B: C is attached to CH3 (3 H) and two ring CH2 groups (2 + 2 H)
α-H = 3 + 2 + 2 = 7
C: C is attached to the CH2 of ethyl (2 H) and two ring CH2 groups (2 + 2 H)
α-H = 2 + 2 + 2 = 6
D: C is attached to the CH2 of ethyl (2 H), a ring CH2 (2 H) and the ring CH carrying the other ethyl group (1 H)
α-H = 2 + 2 + 1 = 5
A and C have the same number of hyperconjugation structures (6 each).
Answer: (3)