Consider the bond dissociation energies listed below in kcal/mol.
CH₃-Br 70
CH₃CH₂-Br 68
(CH₃) ₂CH-Br 68
(CH₃) ₃C-Br 65
These data show that the carbon-bromine bond is weakest when bromine is bound to a ________.

Question

Quizplus · Accepted Answer

The bond dissociation energies show that the carbon-bromine bond is weakest when bromine is bound to a tertiary carbon. This is evident from the fact that the bond dissociation energy is the lowest for the compound that has a tertiary carbon (CH3CBr3), while it is higher for the compounds with secondary (CH3CHBr2), primary (CH3CH2Br), and methyl (CH3Br) carbons. This can be explained by the fact that the more substituted the carbon atom is, the more stable the resulting radical is, due to the greater number of hyperconjugative structures available to delocalize the unpaired electron. As a result, the bond dissociation energy decreases as the number of substituents on the carbon increases, and is lowest for a tertiary carbon.

Consider the Bond Dissociation Energies Listed Below in Kcal/mol