TBR organic chemistry part 1 section 1, comparing example 1.4 to example 1.7

[LimitLess]

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i feel that these 2 examples in the chapter contradict each other, in example 1.4 (page 11) the bond strength is stronger with the more substituted carbon, however in example 1.7 the bond strength is stronger with a primary sp3 carbon. is this due to the chart that we have to follow in example 1.7? if so, do i just follow the common rule that the more substituted the carbon the stronger the bond will be?

 

[PingPongPro]

I think you are reading it wrong. It says bond a is stronger than bond c... BECAUSE bond c contains the more highly substituted carbon.

So more substituted = weaker bond (a stronger than c) (primary stronger than secondary)