Q41P In the presence of a trace of ac... [FREE SOLUTION]

Chapter 20: Q41P (page 1076)

In the presence of a trace of acid, 未-hydroxyvaleric acid forms a cyclic ester (lactone).
HO-CH₂CH₂CH₂CH₂-COOH
未-hydroxyvaleric acid
(a)Give the structure of the lactone, called 未-valerolactone.
(b) Propose a mechanism for the formation of 未-valerolactone.

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About hydroxyvaleric acid

The organic compound that has hydroxyl group and COH group at the terminals of the five-membered acyclic parent chain is hydroxyvaleric acid.

This compound is also called 5-hydroxypentanoic acid.

About the reaction

The five-membered acyclic compound becomes a six-membered ring when hydroxyvaleric acid is treated with a trace of acid. The ring contains one oxygen atom in place of carbon and one carbonyl group attached to the ring.

The structure is given below.

Structure of 未-valerolactone

About the mechanism

The lone pair of electrons present in the carbonyl oxygen attacks the acid leading to the resonance structures.

On rearrangement, there will be the development of a positive charge on the oxygen which is then attacked by an anion followed by the attack of acid. The removal of water forms the desired product.