Amines are more basic in nature than ammonia because in amines alkyl groups are present, which have +I effect, therefore. They increase electron density on nitrogen atom; therefore, amines can donate electron pair more easy than ammonia. On the basis above conclusion the expected order of basic nature of amines is 3°amine > 2°amine > 1° amine (basis of Inductive effect) in gaseous state)
But actual order is 2° amine > 1°amine > 3°amine this anomalous behavior of amines is explained as follows:
Actually basic
nature of amines not only depends upon electron density available on nitrogen
atom, but also depends upon stability of conjugate acid (Solvation effect) that
amines form in aqueous solutions. The stability of conjugate acid in turn
depends upon the extent of hydrogen bonding. Greater the extent of hydrogen
bonding stronger is the conjugate acid and more is the basic nature of
amines. on the basis of stability of conjugate acid (Solvation effect)
the expected order of basic nature of amines is 1° amine > 2°amine 3°amine
But net result of the
two opposing factors (Inductive and Solvation effect) the net basic strength order is as 2°amime > 1° amine > 3°amine.
Related Questions:
(8) Give an explanation for the fact that Guanidine NH=C(CH3)2 is a stronger base than most of amines?
(11) Give an explanation for the fact that Guanidine NH=C(CH3)2 is a stronger base than most of amines?
this is the case when its R is methyl,
ReplyDeletebut order gets changed to 2°>3°>1° when R is ethyl. please give reason for the same.