Which of the following compounds possesses the C-H bond with the lowest bond dissociation energy?

Options

(a) Toluene
(b) Benzene
(c) n-Pentane
(d) 2,2-Dimethylpropane

Correct Answer:

Toluene

Explanation:

Structure of Toluene:

Toluene (C₆H₅CH₃) = 85 kcal/mol

Benzene (C₆H₆) = 110 kcal/mol

n-Pentane (CH₃CH₂CH₂CH₃ ) = 98 kcal/mol

2, 2-Dimathylpropane = 92 kcal/mol

Toluene has the lowest C – H bond dissociation energy compare to other three.

Toluene is a Tertiary free radical. Bond Dissociation Energy of C-H bonds decreases as we go from methyl to primary to secondary to tertiary. They are easier to break since homolytic bond cleavage results in a more stable radical.