(1) |
(2)\[C{{H}_{3}}-C{{H}_{2}}-N{{H}_{2}}\] |
| (3)\[{{(C{{H}_{3}})}_{2}}NH\] | (4)\[C{{H}_{3}}-\overset{O}{\mathop{\overset{||}{\mathop{C}}\,}}\,-N{{H}_{2}}\] |
A) 2>1>3>4
B) 1>3>2>4
C) 3>1>2>4
D) 1>2>3>4
Correct Answer: B
Solution :
[b] Guanidine is most basic because its conjugate acid is stabilized by two equivalent resonance structures,. \[C{{H}_{3}}-\overset{NH}{\mathop{\overset{||}{\mathop{C}}\,}}\,-N{{H}_{2}}\xrightarrow{{{H}^{+}}}C{{H}_{3}}-\overset{N{{H}_{2}}}{\mathop{\overset{|}{\mathop{C}}\,{{}^{+}}}}\,-N{{H}_{2}}\] \[\overset{{}}{\longleftrightarrow}C{{H}_{3}}-\overset{^{+}N{{H}_{2}}}{\mathop{\overset{||}{\mathop{C}}\,}}\,-N{{H}_{2}}\overset{{}}{\longleftrightarrow}C{{H}_{3}}-\overset{N{{H}_{2}}}{\mathop{\overset{|}{\mathop{C}}\,}}\,=\overset{+}{\mathop{N}}\,{{H}_{2}}\] Further \[2{}^\circ \] amines are more basic than\[1{}^\circ \], while amides are least basic due to delocalisation of the lone pair of electrons on N \[C{{H}_{3}}-\overset{:O:}{\mathop{\overset{||}{\mathop{C}}\,}}\,-\overset{..}{\mathop{N}}\,{{H}_{2}}\overset{{}}{\longleftrightarrow}C{{H}_{3}}-\overset{{{\overset{..}{\mathop{:O:}}\,}^{-}}}{\mathop{\overset{|}{\mathop{C}}\,}}\,=\overset{+}{\mathop{N}}\,{{H}_{2}}\] Thus the correct order of basicities is \[C{{H}_{3}}-\overset{NH}{\mathop{\overset{||}{\mathop{C}}\,}}\,-N{{H}_{2}}>C{{H}_{3}}-\overset{C{{H}_{3}}}{\mathop{\overset{|}{\mathop{N}}\,}}\,H>C{{H}_{3}}C{{H}_{2}}N{{H}_{2}}>C{{H}_{3}}-\overset{O}{\mathop{\overset{||}{\mathop{C}}\,}}\,-N{{H}_{2}}\]
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