Why is more substituted C--C bond more stable??

[johnwandering]

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I know the answer, but after a long acid/base binge im having trouble conceptualizing this.

A.) H3C---CH3
B.). (CH3)3C---C(CH3)3


I was wondering why exactly B was a stronger bond than A
Because when B splits, it results in more stable ions (charge is diffused) than if A is split.

Because splitting B would result in more stable species, wouldnt it be a weaker bond? Why is this line of thought incorrect?
)

 

[johnwandering]

Also, again considering the more A/B rules

CH3--Br
Is stronger than
C(CH3)3--BR

Because CH3+ is more unstable than
C(CH3)3+

Why does C--C bonds not follow this rule,

 

[MedPR]

I know the answer, but after a long acid/base binge im having trouble conceptualizing this.

A.) H3C---CH3
B.). (CH3)3C---C(CH3)3


I was wondering why exactly B was a stronger bond than A
Because when B splits, it results in more stable ions (charge is diffused) than if A is split.

Because splitting B would result in more stable species, wouldnt it be a weaker bond? Why is this line of thought incorrect?
)

Are you sure B is stronger than A? What question are you referring to?

 

[johnwandering]

Oh wait the question is for alkenes

It takes more energy to break
(H3C)2C==C(CH3)2

Than it does to break

H2C==CH2

Same concept~~

BR orgo book, chapter 1 question #1 (first set of review qs)

 

[MedPR]

Oh wait the question is for alkenes

It takes more energy to break
(H3C)2C==C(CH3)2

Than it does to break

H2C==CH2

Same concept~~

BR orgo book, chapter 1 question #1 (first set of review qs)

It's not the same concept.

There are empty anti-pi orbitals in alkenes and more substituents are more stable due to hyperconjugation.

 

[deleted92121]

alkyl groups are electron-donating and contribute electron density to the pi bond thus stabilizing the bond and increasing the strength.

 

[johnwandering]

Thanks~

This anti-orbital business goes wayyyyy over my head
Why does this not happen with sigma bonds? (why cant substitients donate e to stabilize sigma bonds)?

 

[deleted92121]

Thanks~

This anti-orbital business goes wayyyyy over my head
Why does this not happen with sigma bonds? (why cant substitients donate e to stabilize sigma bonds)?

I think it is because the energy needed to break a sigma bond is greater than the energy needed to break a pi bond so the sigma bond is already pretty stable. It also may have something to do with geometry and bond angles being less in an alkane vs an alkene.

Just know that alkyl groups stabilize a double bond due to electron donation. That is the main point of all this.

Best of luck!