Question

Given

The enthalpy of the hydrogenation of these compounds will be in the order as

• A. III > II > I
• B. II > III > I
• C. II > I > III
• D. I > II > III

Answer 1

Answer: (A)

$R-CH=CH-R+\underset{\left(1 m o l e\right)}{H_{2}} \rightarrow R-CH_{2}-CH_{2}-R+\Delta H\left(\right.Heatofhydrogenation\left.\right)$
Enthalpy of hydrogenation $ \propto \frac{1}{s t a b i l i t y o f a l k e n e} \propto \frac{1}{N u m b e r o f \alpha - H a t o m s}$
Stability order I > II > III.
Heat of hydrogenation order III > II > I