Question

A hydroxy acid on heating gives a $5$-membered lactone. The acid is

• A. $CH _{2} OHCH _{2} CH _{2} COOH$
• B. $ CH_{3}CHOHCH_{2}COOH $
• C. $ CH_{3}CH_{2}CHOHCOOH $
• D. $ CH_{3}CHOHCHOHCOOH $

Answer 1

Answer: (A)

$ \gamma $ or $ \delta $ -hydroxy acids, on heating, give lactones, having same number of carbon atoms as the parent acid.
Thus, $\overset{\gamma}{C} H _{2} OH \overset{\beta}{ C } H _{2} \overset{\alpha}{ C } H _{2} COOH$ gives five membered lactone.
$\underset{\overset{|}{OH}}{C} H _{2} CH _{2} CH _{2} \underset{\overset{|}{OH}}{C} = O \ce{->[{\Delta}][{-H_2O}]}$