Bond dissociation enthalpies 2-methylpropane

Similarly, by comparing the bond dissociation enthalpies of the two different types of C—H bonds in 2-methylpropane, we see that a tertiary radical is 22 kJ/mol (6 kcal/ mol) more stable than a primary radical. 

The benzylic position in alkylbenzenes is analogous to the allylic position in alkenes. Thus a benzylic C—H bond, like an allylic one, is weaker than a C—H bond of an alkane, as the bond dissociation enthalpies of toluene, propene, and 2-methylpropane attest ... 

As in Section 10.3 where we counted the decreased bond-dissociation enthalpy in propene compared with 2-methylpropane as evidence for stabilization of allyl radical by delocalization of the unpaired electron, we attribute the decreased C—H bond strength in toluene versus propene as reflecting better electron delocalization in benzyl radical versus allyl. 

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