Chapter 23, Problem 34P

Interpretation Introduction

Interpretation:

Structures of compound B (${\text{C}}_{\text{6}}{\text{H}}_{\text{6}}{\text{O}}_{\text{2}}{\text{, mp 54}}^{\text{o}}\text{C}$) and compound C are to be determined on the basis of the following information. Compound B is formed along with $\text{1, 2-ethanediol}$ on hydrolysis of the acetal function of the given compound A in dilute sulfuric acid. Compound B exhibits a carbonyl stretching band in infrared at 1690 ${\text{cm}}^{-1}$, and has two singlets in its proton NMR spectrum at $\text{δ}$ 2.9 and 6.7 in $\text{2:1}$ ratio. On standing in water or ethanol, compound B is converted cleanly to an isomeric substance, compound C (${\text{mp 172-173}}^{\text{o}}\text{C}$).

Concept Introduction:

Acetals are geminal diol or diether derivatives of aldehydes or ketones, formed by the reversible addition of two moles of water or alcohol to the carbonyl group in acidic conditions.

Hydrolysis of a cyclic acetal in acidic conditions yields the original carbonyl compound and a diol.

Ketones reversibly undergo enolization in aqueous solutions. If the enolization leads to aromatiziation, the higher stability of aromatic ring can drive the isomerization to complete enolization.