The correct increasing order of basic strength of amine is:
(A) \(C_6H_5NH_2 < NH_3 < C_6H_5CH_2NH_2 < C_2H_5NH_2 < (C_2H_5)_2NH\)
(B) \(NH_3 < C_6H_5NH_2 < C_6H_5CH_2NH_2 < C_2H_5NH_2 < (C_2H_5)_2NH\)
(C) \(C_6H_5CH_2NH_2 < C_6H_5NH_2 < NH_3 < C_2H_5NH_2 < (C_2H_5)_2NH\)
(D) \(C_2H_5NH_2 < (C_2H_5)_2NH < C_6H_5NH_2 < NH_3\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) only
The basic strength of an amine depends on how freely its nitrogen lone pair is available for a proton. Aniline is the weakest of these bases (lone pair delocalised into the ring); \( \ce{NH3} \) is stronger; in benzylamine the \( \ce{CH2} \) group keeps the lone pair out of resonance, so it is stronger than \( \ce{NH3} \) but weaker than ethylamine (−I effect of phenyl); alkyl groups raise basicity by +I effect, and in water \( \ce{(C2H5)2NH} \) is stronger than \( \ce{C2H5NH2} \).
(A) \( \ce{C6H5NH2} \) < \( \ce{NH3} \) < \( \ce{C6H5CH2NH2} \) < \( \ce{C2H5NH2} \) < \( \ce{(C2H5)2NH} \) — Correct order. Every step follows the points above.
(B) \( \ce{NH3} \) < \( \ce{C6H5NH2} \) < \( \ce{C6H5CH2NH2} \) < \( \ce{C2H5NH2} \) < \( \ce{(C2H5)2NH} \) — Incorrect order. It puts \( \ce{NH3} \) below aniline; aniline is the weaker base.
(C) \( \ce{C6H5CH2NH2} \) < \( \ce{C6H5NH2} \) < \( \ce{NH3} \) < \( \ce{C2H5NH2} \) < \( \ce{(C2H5)2NH} \) — Incorrect order. It puts benzylamine below aniline and \( \ce{NH3} \); benzylamine is stronger than both.
(D) \( \ce{C2H5NH2} \) < \( \ce{(C2H5)2NH} \) < \( \ce{C6H5NH2} \) < \( \ce{NH3} \) — Incorrect order. It makes the alkylamines weaker than aniline and \( \ce{NH3} \), the reverse of the real order.