Which of the following orders is correct for heat of hydrogenation of these compounds?

I I I > I I > I

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I I > I I I > I

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I I I > I > I I

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I > I I > I I I

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Solution

The correct option is A $I I I > I I > I$
Heat of hydrogenation is directly propotional to the number of $π$ bonds and inversly propotional to the stability of alkene. So, in (III), there are two $π$ bonds, hence the heat of hydrogenation will be maximum. In between (I) and (II), (II) has 4 alpha hydrogens and (I) has 10 alpha hydrogens. So, (I) will be more stable than (II). Hence, heat of hydrogenation is more in (II) than (I).

Hence, the correct order will be $I I I > I I > I$

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