Q. 8-8-72E - Organic Chemistry (Mcmurry)

Question

Compound A, ${\mathbf{C}}_{\mathbf{11}}{\mathbf{H}}_{\mathbf{16}}\mathbf{O}$, was found to be an optically active alcohol. Despite its apparent unsaturation, no hydrogen was absorbed on catalytic reduction over a palladium catalyst. On treatment of A with dilute sulfuric acid, dehydration occurred and an optically inactive alkene B, ${\mathbf{C}}_{\mathbf{11}}{\mathbf{H}}_{\mathbf{14}}$, was the major product. Alkene B, on ozonolysis, gave two products. One product was identified as propanal, ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{CHO}$. Compound C, the other product, was shown to be a ketone, ${\mathbf{C}}_{\mathbf{8}}{\mathbf{H}}_{\mathbf{8}}\mathbf{O}$. How many degrees of unsaturation does A have? Write the reactions, and identify A, B, and C.

Step-by-Step Solution

Answer

Compound A has four degrees of unsaturation.

Degree of unsaturation

It is also known as the Index of Hydrogen Efficiency (IHD). It determines the number of rings and bonds.

Compound A has four degrees of unsaturation due to three double bonds in a ring and one ring residue.

$\mathrm{Degree} \mathrm{of} \mathrm{unsaturation} : \mathrm{ring}+\mathrm{\pi } \mathrm{bond}=\mathrm{C}-\frac{\mathrm{H}}{2}-\frac{\mathrm{X}}{2}+\frac{\mathrm{N}}{2}$

Explanation of reagents

On the treatment of A with dilute sulfuric acid, dehydration occurs and an optically inactive alkene B, ${\mathrm{C}}_{11}{\mathrm{H}}_{14}$

Alkene B, on ozonolysis, gives two products. One product is propanal ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{CHO}$and the other is ketone, ${\mathrm{C}}_8{\mathrm{H}}_8\mathrm{O}$

Chemical reactions of compound A