Pheny group. Electron donating or withdrawing?

[DATkiller]

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Hey guys. I was just wondering if you guys know if benzene is electron donating or withdrawing. Knowing that can help you determine the strength of acid or base compounds when benzene is attached to them. Like benzoic acid for example.

 

[Marmar tala]

b/c of the resonance it adds to the stability of the anion that forms, therefore make it more stable => stronger acid
I don't know if it has withdrawing or donating effect, though.

 

[orgohacks]

b/c of the resonance it adds to the stability of the anion that forms, therefore make it more stable => stronger acid
I don't know if it has withdrawing or donating effect, though.

That's a key point actually. the pKa of phenol (Ph-OH) is significantly higher (10) than that of H2O and other alcohols (~16) because of the resonance. Probably best to look at it that way.

 

[Baylor2011]

e- donating group (activating)

 

[DATkiller]

That makes sense since benzoic acid is more basic than methanoic acid.

 

[CANgnome]

draw the resonance forms of a deprotonated phenol and you will be able to tell if it is donating or withdrawing

 

[Munks]

Bah this question's got me confused quite a bit.

I know that phenyl substituents are weakly activating (ortho/para directors, thus electron donating) when put on another benzene ring, similar to added aliphatic substituents.

But, if the pKa is lower (stronger acid) on phenol than water or an aliphatic alcohol, wouldn't that mean that it's electron withdrawing? I don't know exactly what happens for an oxygen anion, but I know Ph-H is more acidic than CH4 (lower pKa).... Wouldn't that mean it is electron withdrawing, because if it were electron donating, then the added electrons would further destabilize the resulting carbanion?

Or am I just completely out of wack as previously stated?