Which one of the following dienes will have the lowest heat of hydrogenation?
A) I
B) II
C) III
D) IV
E) V

Question

Which one of the following dienes will have the lowest heat of hydrogenation? 
A) I 
B) II 
C) III 
D) IV 
E) V

Quizplus · Accepted Answer

The heat of hydrogenation is a measure of the stability of a molecule. The more stable the molecule, the less heat is released during hydrogenation. Dienes with conjugated double bonds are more stable than dienes with isolated double bonds due to the delocalization of electrons through the conjugated system. Among the given options, diene I has the most extended conjugated system with 4 conjugated double bonds, while the others have only 3 conjugated double bonds. Therefore, diene I will be the most stable and will have the lowest heat of hydrogenation.

Which One of the Following Dienes Will Have the Lowest