Question

a. How many alkenes could you treat with H₂, Pd/C to prepare methylcyclopentane?

b. Which of the alkenes is the most stable?

c. Which of the alkenes has the smallest heat of hydrogenation?

Short answer

a) 4 alkenes

b) 1-methyl-cyclopentene is most stable.

c) As 1-methyl-cyclopentene is most stable so this has the smallest heat of hydrogenation

Step-by-step solution

What is the heat of hydrogenation

It is the measure of the stability of an alkene. Lower the heat of hydrogenation of the alkene more stable it is. Alkyl substitution on an unsaturated carbon lowers the heat of hydrogenation and more stable the compound formed. It is due to hyperconjugative effect.

Final answer

a)The reaction which is carried out in presence of H₂, Pd/C is said to be a reduction reaction. Here the product is given is an alkane i.e methyl cyclopentane. Thus the reactant should be an alkene. Hence methyl cyclopentane can be prepared from the possible isomers of methyl cyclopentane

b) 1-methyl-cyclopentene is most stable because methyl group and double bond is on the same carbon atom.

c) As 1-methyl-cyclopentene is most stable so this has the smallest heat of hydrogenation.