Which of the following is strongest Bronsted base?
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Answer
(4) [figure]
Solution
Basic strength depends on how free the lone pair on N is:
(A): lone pair delocalised into one benzene ring ⇒ (A) weak base
(B): lone pair delocalised into two rings ⇒ (B) weaker
(C): lone pair is part of the aromatic sextet (6π) of pyrrole ⇒ (C) almost non-basic
(D): sp3 N, lone pair localised, +I of alkyl groups ⇒ (D) strongest
∴ (D) > (A) > (B) > (C)
Answer: (4)