Neet Solved Paper 2013 Question 44
Question: The order of stability of the following tatutomeric compound is $ \underset{I}{\mathop{CH{ _2}\text{=}\overset{\begin{smallmatrix} OH \\ | \end{smallmatrix}}{\mathop{C}},\text{-C}{H_2}\text{-CH}{ _2}-\overset{\begin{smallmatrix} OH \\ |\text{ }| \end{smallmatrix}}{\mathop{C}},\text{-C}{H_3}}}, $ $ \underset{II}{\mathop{CH{ _3}\text{=}\overset{\begin{smallmatrix} OH \\ | \end{smallmatrix}}{\mathop{C}},\text{-C}{H_2}-\overset{\begin{smallmatrix} OH \\ |\text{ }| \end{smallmatrix}}{\mathop{C}},\text{-C}{H_3}}}, $ $ \underset{III}{\mathop{C{H_3}\text{-}\overset{\begin{smallmatrix} OH \\ | \end{smallmatrix}}{\mathop{C}},\text{=CH-}\overset{\begin{smallmatrix} O \\ |\text{ }| \end{smallmatrix}}{\mathop{C}},\text{-C}{H_3}}}, $
Options:
A) $ I>II>III $
B) $ III>II>I $
C) $ II>I>III $
D) $ II>III>I $
Show Answer
Answer:
Correct Answer: B
Solution:
The rolls of $ \beta\text{ -} $ dicarbonyl compounds are more stable because of conjugation and intermolecular H-bonding.
Thus, the order of stability is
$ \underset{III}{\mathop{\underset{\begin{smallmatrix} \text{(Stabilised},by,conjugation \\ and,\text{H-bonding)} \end{smallmatrix}}{\mathop{{H_3}C-\overset{\begin{smallmatrix} OH \\ | \end{smallmatrix}}{\mathop{C}},\text{=},CH-\overset{\begin{smallmatrix} O \\ |\text{ }| \end{smallmatrix}}{\mathop{C}},-C{H_3}}},}}$ $ \text{},C{H_3}-\overset{\begin{smallmatrix} O \\ |\text{ }| \end{smallmatrix}}{\mathop{C}},-\underset{II}{\mathop{C{H_2}}},-\overset{\begin{smallmatrix} O \\ |\text{ }| \end{smallmatrix}}{\mathop{C}},-C{H_3} $ $ \underset{I}{\mathop{\underset{\begin{smallmatrix} Less,Stable,as,\text{(=)bond} \\ is,not,in,conjugation,with,carbonyl,group \end{smallmatrix}}{\mathop{\text{},C{H_3}=\overset{\begin{smallmatrix} O \\ | \end{smallmatrix}}{\mathop{C}},-C{H_2}-\overset{\begin{smallmatrix} O \\ |\text{ }| \end{smallmatrix}}{\mathop{C}},-C{H_3}}},}}, $
