Question

Which of the following is a tautomer of

$C{H}_3-\underset{\stackrel{||}{O}}{C}-H$?

• A. $C{H}_3-\underset{\stackrel{||}{O}}{C}-C{H}_3$
• B. $C{H}_2=\underset{\stackrel{|}{OH}}{CH}$
• C. $C{H}_3-C{H}_2-CHO$
• D. $C{H}_3-COOH$

Answer 1

The correct option is B

$C{H}_2=\underset{\stackrel{|}{OH}}{CH}$

It is a phenomenon in which a single compound exists in two readily interconvertible structures that differ in the relative position of atleast one atomic nucleus, generally hydrogen.

Tautomeric structures are obtained by the simultaneous shift of H atom and double bond at1 and 3 position.That is why it is also called 1,3-shift. It is further called desmotropism or dynamic isomerism or kryptomerism.

$-\stackrel{\underset{||}{O}}{C}-\stackrel{\underset{|}{H}}{\underset{\stackrel{|}{\left(Keto\right)}}{C}}\leftrightharpoons -\stackrel{\underset{|}{OH}}{C}=\underset{\stackrel{|}{\left(Enol\right)}}{C}-$

$\to$ One of the major conditions for tautomerism is the presence of an $\alpha$-hydrogen

$\to$ $\alpha$-hydrogen is present on $\alpha$- carbon

Here,

$H-\stackrel{\underset{|}{H}}{\underset{\stackrel{|}{H}}{C}}-\underset{\stackrel{||}{O}}{C}-H\leftrightharpoons C{H}_2=\underset{\stackrel{|}{OH}}{CH}$