Arrange the following in increasing order of basic strength in aqueous solution:
(A) $C_6H_5NH_2$
(B) $C_2H_5NH_2$
(C) $(C_2H_5)_2NH$
(D) $NH_3$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (D), (B), (C)
The correct order is: C₆H₅NH₂ < NH₃ < C₂H₅NH₂ < (C₂H₅)₂NH
In aqueous solution, the increasing order of basic strength is:
Aniline < Ammonia < Ethylamine < Diethylamine
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(A) C₆H₅NH₂ (Aniline) → Least basic
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The lone pair on nitrogen is delocalized into the benzene ring (resonance).
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This reduces availability of the lone pair for protonation.
⇒ Weakest base
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(D) NH₃ (Ammonia)
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No electron-donating alkyl groups.
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Lone pair is available but not strongly pushed.
⇒ More basic than aniline, but less than alkyl amines.
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(B) C₂H₅NH₂ (Primary amine)
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+I effect of ethyl group increases electron density on nitrogen.
⇒ More basic than NH₃.
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(C) (C₂H₅)₂NH (Secondary amine) → Most basic in aqueous solution
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Stronger +I effect (two alkyl groups).
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Also better solvation than tertiary amines, making it most basic here.
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