If an R group is electron withdrawing - Why do tertiary stabilize carbocations?

[MedicalMan14]

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If an R group is electron withdrawing then why and how do tertiary stabilize Carbocations? Isn't this stabilization in effect the opposite of withdrawing behavior?

 

[EpicBearMan]

An R group, representing a hydrocarbon, is slightly electron donating. The electron donating effect stabilizes a positive charge. R groups don't always stabilize though.

For example, water is a stronger acid than ethanol. The ethyl group, which could be represented by R, is electron donating and decreases the stability of the negative charge in the conjugate base.

In the picture below, notice that -R is in the EDG or "Electron Donating Group" category. The activating / deactivating and ortho / para directing stuff is about electrophilic aromatic substitution, and doesn't really have anything to do with the question.

 

[loveoforganic]

As far as stabilizing carbocations - hyperconjugation.

 

[EpicBearMan]

I think I misunderstood the question the first time. In the context of electron donating / withdrawing groups, -R usually represents a simple alkyl chain, but I see what you meant now.

As for why an EWG stabilizes a carbocation, it looks like that's been answered already.