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The correct sequence regarding base strength of aliphatic amines in gaseous phase is

$\begin{array}{1 1}(a)\;R_2NH > RNH_2 > R_3N > NH_3&(b)\;R_2NH > R_3N > RNH_2 > NH_3\\(c)\;R_3N > RNH_2 > R_2NH > NH_3 &(d)\;R_3N > R_2NH > RNH_2 > NH_3\end{array}$

1 Answer

Toolbox:
  • Due to the electron releasing nature of alkyl group R- in alkanamine , it pushes electrons towards nitrogen and thus makes the unshared electron pair more available for sharing with the proton of the acid. Moreover, the substituted ammonium ion formed from the amine gets stabilised due to dispersal of the positive charge by the +I effect of the alkyl group. Hence, alkylamines are stronger bases than ammonia. Thus, the basic nature of aliphatic amines should increase with increase in the number of alkyl groups. This trend is followed in the gaseous phase.
  • The order of basicity of amines in the gaseous phase follows the expected order: tertiary amine > secondary amine > primary amine > $NH_3$.
Alkyl amines are stronger bases than ammonia because +I effect of the alkyl group.The basic nature of aliphatic amines should increase with increase in the number of alkyl group.
Hence (d) is the correct answer.
answered Feb 27, 2014 by sreemathi.v
edited Mar 29, 2014 by mosymeow_1
 
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