QuestionOrganic / carbocation stability
Which cationic species is more stable in each of the following pairs?
- (a) 1 and 3
- (b) 1 and 4
- (c) 2 and 4
- (d) 2 and 3
Answer: (d) 2 and 3
Pair X: 1 is a primary allylic cation conjugated only with C=CH₂ ending in CH₂; 2 (pent-2-enyl) delocalises + onto a secondary carbon → more stable. Pair Y: 3 (protonated amidine) is stabilised by two NH₂ donors, while 4 (protonated amide) has one NH₂ and OH (O less donating). → 2 and 3 → (d).