Why do halogens increase C-H bond strength?

[IcemanMD]

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According to BR orgo, a halogen increases the bond strength of a C-H bond. Why is this?

I thought that because chloroform (CHCl3) is a stronger acid than dichloromethane, the C-H bond in chloroform is weaker, therefore halogens decrease C-H bond strength...

Specific question I am referencing is Number 6 passage 1 in the Hydrocarbon reactions chapter (pg 290)

 

[1TB4RKSB4CK]

Halogens are EWGs so they stabilize the alkane bond. If the halogen were on a double bond then it would destabilize it.

 

[IcemanMD]

I read that too but I'm not sure why this is...Also doesn't explain the acidity of chloroform.

They even say on pg 272 that the presence of halogens on a molecule increases its acidity. Doesn't this contradict the idea that they make C-H bonds stronger?

 

[chill3]

So chloroform is more acidic because it has more electron withdrawing groups (Cl) on it. What we want to avoid is placing negative charge on the carbon, so the additional Cl helps to delocalize that charge in the conjugate base, therefore making the conj. base more stable and chloroform a strong acid.

As far as bond strength goes, I think there must be some mistake, because I agree that the C-H bond is weaker in a stronger acid per the explanation given above. The C-X bond would be strong... I don't have the BR books, so I can't reference the passage for clarification.