Q 14-14-59 Ec - Organic Chemistry (Mcmurry)

Question

Hydrocarbon A, C₁₀H₁₄, has a UV absorption at${\mathrm{\lambda }}_{\max }=236\mathrm{nm}$ and gives hydrocarbon B, C₁₀H₁₈, on catalytic hydrogenation. Ozonolysis of A, followed by zinc/acetic acid treatment, yields the following di-keto dialdehyde:

c) Write the reactions, showing the starting material and products.

Step-by-Step Solution

Answer

The reaction showing ozonolysis is-

Finding degree of unsaturation

In the analysis of  the molecular formula of organic molecules, the degree of unsaturation is a calculation that determines the total numbers of rings and pi bonds in the system. For finding out the DOU, you can use formula,

$$\begin{gathered} \mathrm{Degree} \mathrm{of} \mathrm{unsaturation}=\frac{1}{2}\times (2+2\times \mathrm{C}-\mathrm{H}+\mathrm{N}-\mathrm{X}) \\ \mathrm{Degree} \mathrm{of} \mathrm{unsaturation}=\frac{1}{2}\times (2+2\times 10-14+0-0) \\ \mathrm{Degree} \mathrm{of} \mathrm{unsaturation}=\frac{1}{2}\times (2+2\times 10-14+0-0) \\ \mathrm{Degree} \mathrm{of} \mathrm{unsaturation}=\frac{1}{2}\times (22-14) \\ \mathrm{Degree} \mathrm{of} \mathrm{unsaturation}=4 \end{gathered}$$

From the formula , degree of saturation for A comes out to be 4 and  as you can see that  the ozonolysis product contains all the carbons and di-keto dialdehyde are there, so one can  say, there are 2 rings and 2 double bonds in A.

Prediction of two structures

The structures which can be in agreement with the information drawn above come out to be,

                                   Structures proposed

Reaction

Structure II is the structure which can give Diels-Alder adduct on reaction with maleic anhydride through Diels-Alder reaction. And Diels-Alder reaction is possible in structure II only because in that structure it is possible for the double bonds to assume s-cis conformation through free rotation about the single bond, which is an essential condition for Diels-Alder reaction to occur.

ozonolysis, Diels-Alder reaction, Catalytic hydrogenation of A

Ozonolysis

                                                        Ozonolysis

Diels-Alder reaction

                                         Diels-Alder reaction

Catalytic hydrogenation

                                 Catalytic hydrogenaation