Question
Chemistry Question on Hydrocarbons
Which one of the following has the smallest heat of hydrogenation per mole ?
A
1-butene
B
trans-2-butene
C
cis-2-butene
D
1,3-butadiene
Answer
trans-2-butene
Explanation
Solution
Among alkenes-heat of hydrogenation depends on :
(a) The number of double bonds-greater the number of double bonds, greater the amount of heat evolved in hydrogenation.Hence, 1, 3-butadiene has highest heat of hydrogenation among these.
(b) Relative stability of alkenes-greater the stability, smaller the heat evolved in hydrogenation. Trans-2-butene is most stable among three given butenes, has least heat of hydrogenation.