Question

Which has maximum heat of hydrogenation?
A)

B)

C)

D) All have same values

Answer 1

Hint: We must have to know that the heat of hydrogenation is inversely proportional to the stability of a molecule. Benzene is highly stable in nature. Heat of hydrogenation is the measure of carbon double bond carbon. The smaller the value of heat of hydrogenation stronger is the double bond.

Complete answer:
We also remember that heat of hydrogenation is the stability of an alkene formed. In hydrogenation reactions, the bond is broken or formed; this defines the stability of an alkene and the heat of hydrogenation whether lower or higher.
Option A) this is an incorrect option as this structure is known as benzene and it is aromatic in nature and most stable among all the options given thus it has minimum value of heat of hydrogenation as the more stable the molecule less value for heat of hydrogenation.
Option B) This option is correct as this is 1,4 cyclohexadiene. It is a non-conjugated diene as the double bonds do not lie in conjugation thus it is least stable due to which maximum value for heat of hydrogenation.
Option C) this is an incorrect option.
Option D) this is an incorrect option as all the options will have different values for heat of hydrogenation depending upon the stability.

Note:
We have to remember that hydrogenation is nothing but chemical bond formation between hydrogen atoms and other molecules or compounds. The higher the double bond stability, minimum will be the value for heat of hydrogenation. Benzene is the most stable molecule with complete conjugation in it.