MCQ
Which (isomeric) amine has lowest boiling point ?
- A$1^o \,amine$
- B$2^o \,amine$
- ✓$3^o \,amine$
- Dcannot predict
✓
Answer
Correct option: C.
$3^o \,amine$
c
Primary and secondary amines also form hydrogen bonds, so these amines have higher boiling points than alkanes with similar molecular weights. Nitrogen is not as electronegative as oxygen, however, which means that the hydrogen bonds between amine molecules are weaker than the hydrogen bonds between alcohol molecules. Amines, therefore, have lower boiling points than alcohols with similar molecular weights.
Primary and secondary amines also form hydrogen bonds, so these amines have higher boiling points than alkanes with similar molecular weights. Nitrogen is not as electronegative as oxygen, however, which means that the hydrogen bonds between amine molecules are weaker than the hydrogen bonds between alcohol molecules. Amines, therefore, have lower boiling points than alcohols with similar molecular weights.
Because primary amines have two $\mathrm{N}$$- H$ bonds, hydrogen bonding is more sign ificant for primary amines than for secondary amines. Tertiary amines cannot form hydrogen bonds with each other because they do not have a hydrogen attached to the nitrogen Consequent ly, if you compare amines with the same molecular weight and similar structures, primary amines have higher boiling points than secondary amines, and secondary amines have higher boiling points than tertiary amines.
$\underset{\begin{smallmatrix}
a\,primary\,a\min e \\
b.pt=97{{\,}^{o}}C
\end{smallmatrix}}{\mathop{\begin{matrix}
\,\,\,\,C{{H}_{3}} \\
|\,\,\, \\
C{{H}_{3}}C{{H}_{2}}CHC{{H}_{2}}N{{H}_{2}} \\
\end{matrix}}}\,$ $\underset{\begin{smallmatrix}
a\,\sec ondary\,a\min e \\
b.pt=84{{\,}^{o}}C
\end{smallmatrix}}{\mathop{\begin{matrix}
\,\,\,\,C{{H}_{3}} \\
|\,\,\, \\
C{{H}_{3}}C{{H}_{2}}CHNHC{{H}_{3}} \\
\end{matrix}}}\,$ $\underset{\begin{smallmatrix}
a\,tertiary\,a\min e \\
b.pt=65{{\,}^{o}}C
\end{smallmatrix}}{\mathop{\begin{matrix}
\,\,\,\,\,C{{H}_{3}} \\
\,\,|\,\,\, \\
C{{H}_{3}}C{{H}_{2}}NC{{H}_{2}}C{{H}_{3}} \\
\end{matrix}}}\,$
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