Question

The same alkane is obtained from the catalytic hydrogenation of both alkene $A$ and alkene B. The heat of hydrogenation of alkene $A$ is 29.8 kcal/mol $(125 \mathrm{kJ} / \mathrm{mol}),$ and the heat of hydrogenation of alkene $\mathrm{B}$ is $31.4 \mathrm{kcal} / \mathrm{mol}(131 \mathrm{kJ} / \mathrm{mol}) .$ Which alkene is more stable?

Name: Problem 27, Chapter 4: Organic Chemistry
Uploaded: 2021-04-03T15:50:39-08:00
Duration: 2 min 35 s
Channel: Shazia Naz
Description: The same alkane is obtained from the catalytic hydrogenation of both alkene A and alkene B. The heat of hydrogenation of alkene A is 29.8 kcal/mol (125 kJ / mol), and the heat of hydrogenation of alkene B is 31.4 kcal / mol(131 kJ / mol) . Which alkene is more stable?

   The same alkane is obtained from the catalytic hydrogenation of both alkene $A$ and alkene
B. The heat of hydrogenation of alkene $A$ is 29.8 kcal/mol $(125 \mathrm{kJ} / \mathrm{mol}),$ and the heat of hydrogenation of alkene $\mathrm{B}$ is $31.4 \mathrm{kcal} / \mathrm{mol}(131 \mathrm{kJ} / \mathrm{mol}) .$ Which alkene is more stable?

Organic Chemistry

Paula Yurkanis… 4th Edition

Chapter 4, Problem 27

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Solved by Expert Shazia Naz

04/03/2021

Step 1

The heat of hydrogenation is inversely proportional to the stability of the alkene. This means that the more stable the alkene, the less heat is released during hydrogenation. Show more…

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The same alkane is obtained from the catalytic hydrogenation of both alkene $A$ and alkene B. The heat of hydrogenation of alkene $A$ is 29.8 kcal/mol $(125 \mathrm{kJ} / \mathrm{mol}),$ and the heat of hydrogenation of alkene $\mathrm{B}$ is $31.4 \mathrm{kcal} / \mathrm{mol}(131 \mathrm{kJ} / \mathrm{mol}) .$ Which alkene is more stable?

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Key Concepts

Heat of Hydrogenation

Heat of hydrogenation is the energy change that occurs when an unsaturated compound such as an alkene is converted into a saturated compound (alkane) by the addition of hydrogen. A lower magnitude of heat release generally indicates that the original alkene is more stable since it is already closer in energy to the saturated product.

Alkene Stability

Alkene stability refers to the relative energy of alkenes, where more stable alkenes have lower internal energy. This stability is often inferred from the heat of hydrogenation, with a lower heat release suggesting a more stable double bond configuration.

Catalytic Hydrogenation

Catalytic hydrogenation is a reaction in which hydrogen is added to a compound across a double or triple bond with the assistance of a catalyst, typically converting alkenes into alkanes. The reaction’s exothermic nature allows for the comparison of the relative stability of different alkenes based on the energy released.

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