[nj_bartel]

There's a peak at ~164 ppm, it's not the carbonyl peak.  I can't decide whether it would be the aryl carbon attached to the carbonxyl substituent or the aryl carbons meta to the carboxyl substituent.

Any words of assistance?

[Squirmy]

Good question!

I think you're seeing a combination of inductive and resonance effects for each substituent.

I think looking at the C13 spectra of benzoic acid and anisole would simplify the analysis. SDBS has both.

http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi

[nj_bartel]

Ok, now i'm very confused.  The SDB has the substituted aryl carbon of anisole at 159 ppm.  So combine that with a para carboxylic acid substituent and you'd get the slightly higher shift to 164 ppm.  Why is the substituted aryl carbon in anisole so deshielded?  I was under the impression the inductive and resonance effects of alkoxy substituents roughly cancelled each other.

[Squirmy]

The resonance effect of the alkoxy group doesn't affect each carbon of the ring equally. If you look at the resonance structures of anisole, which carbons of the ring bear the charge? What kind of charge is it and what how does that affect chemical shift?

Finally, how much of an effect would you expect on the carbons with no charge?

The inductive effect doesn't affect each carbon equally, either...it's more about distance from the electron withdrawing group

[nj_bartel]

Negative charges in the ortho/para positions.  The negative charge serves to shield the carbon.  On the carbons with no charge I would expect a tiny deshielding due to inductive effects (at least in the ortho position, not para), as well as on the position of substitution (with the most deshielding at this position).

Thanks for pointing me in the right direction, I wasn't really looking at the alkoxy substituent in the right way.

And the carboxylic acid is also ortho/para deshielding, correct?  That would make sense.

[Squirmy]

That's what I was thinking...and looking at chloro- and bromobenzene and aniline, it still checks out. The chemical shift of the carbon w/ the substituent correlates nicely with electronegativity trends.

[nj_bartel]

Thanks, very helpful 

[Squirmy]

No problem...I thought it was interesting and learned something new