Question

The incorrect order for amines among the following is
A. Order of basicity in aqueous medium.
$C{H_3} - NH - C{H_3} > C{H_3}N{H_2} > {(C{H_3})_3}N$$C{H_3} - NH - C{H_3}$
B. Order of boiling point.
\[{(C{H_3})_3}N > C{H_3} - C{H_2} - NH - C{H_3} > C{H_3} - C{H_2} - C{H_2} - N{H_2}\]
C. Order of basicity in gaseous state.
\[{(C{H_3})_3}N > C{H_3} - NH - C{H_3} > C{H_3}N{H_2}\]\[{(C{H_3})_3}N > C{H_3} - NH - C{H_3} > C{H_3}N{H_2}\]
D. Order of aqueous solubility. \[{(C{H_3})_3}N < C{H_3} - C{H_2} - NH - C{H_3} < C{H_3} - C{H_2} - C{H_2} - N{H_2}\]

Answer 1

Hint:Basicity is defined as the tendency to donate lone pairs of electrons. More easily the electron can be donated, more is the basicity. The boiling point order can be calculated by taking into consideration the Hydrogen bonding tendency.

Complete step by step answer:
-Nitrogen has one lone pair of electrons that can be donated thus showing the basic character as basic strength depends on electron donating tendency. The order of basicity in aqueous solution is $C{H_3} - NH - C{H_3} > C{H_3}N{H_2} > {(C{H_3})_3}N$ .
-Due to weak intermolecular Hydrogen bonding, the boiling point of primary and secondary amines are lower than those of alcohols of comparable molecular weight. The boiling point of tertiary amines which have no hydrogen bonds are near to those of alkanes of comparable molecular weight. Thus the order of boiling point of amines is $(C{H_3})_3N < C{H_3} - C{H_2} - NH - C{H_3} < C{H_3} - C{H_2} - C{H_2} - N{H_2}$
-The order of basicity of amines in gaseous state depends on the stability of carbocation formed after donating the lone pair of electrons present on the nitrogen atom. This order is \[{(C{H_3})_3}N > C{H_3} - NH - C{H_3} > C{H_3}N{H_2}\]\[{(C{H_3})_3}N > C{H_3} - NH - C{H_3} > C{H_3}N{H_2}\] as tertiary carbocation is most stable whereas primary carbocation is least stable.
-The water solubility of amines decreases with increasing size of alkyl group having order as
\[{(C{H_3})_3}N < C{H_3} - C{H_2} - NH - C{H_3} < C{H_3} - C{H_2} - C{H_2} - N{H_2}\]

From the observation we can say that the option having incorrect order is B. And hence option B is the correct answer.


Note:
Amines are derivatives of ammonia in which one or more hydrogen atoms are replaced by alkyl groups. Mixtures of ${1^ \circ },{2^ \circ }$ and ${3^ \circ }$ amines can be separated by fractional distillation ,Hinsberg method, Hofmann method.