[mjb5676]

I am having some difficulties classifying the peaks of my  400MHz Carbon-13 NMR. This is an C13 NMR of 3-carbethoxycoumarin. Looking at the chemical shift ranges, I have made some predictions as to which peak belongs to which carbon. I run into trouble with the 120-170 PPM range. I know there is an aromatic ring and keytones that lie within this range. If anyone could let me know which ones are right or wrong, so I can go back and make corrections, that would be swell. Thank you.

Attached is the 400MHz C-13 NMR of 3-carbethoxycoumarin

Sorry about the photo being upside-down. It's fixed now

[discodermolide]

Could you please turn the picture 180°?

[Babcock_Hall]

Carbon-7 is aromatic.  The 1:1:1 triplet you see near 77 ppm is probably the solvent, CDCl₃.  Also, the carbonyl carbons are esters, not ketones.  Do you know of a rule of thumb for the intensity of quaternary carbons versus nonquaternary carbons?

[mjb5676]

No, I am not familiar with that. Please do tell.

[Babcock_Hall]

Depending on how the spectra are acquired, quaternary carbons often have lower intensity, all other things held equal. 

[PhDoc]

When 13C nucleii become excited, they relax predominantly via their attached protons. Whenever you have an aldehyde, ketone, nitrile, or quaternary carbon, there are no protons attached, and hence the carbon nucleus doesn't completely relax on the NMR timescale. The result is a peak smaller in intensity than one related to a carbon bearing hydrogen(s).

Please see Pavia, Lampman and Kriz... Introduction to Spectroscopy, 3rd Edition.

[Babcock_Hall]

Is the peak marked 5 really two peaks?

[mjb5676]

Thanks for your input everyone! I think I have fixed it, or at least more correct. The peak numbered 5 is two peaks. With that in mind, the new numbering of the peaks, from left to right are: 8, 3, 5, 12, 11, 10, 4, 6, 9, solvent CDCL₃, 2, 1. I am not quite sure with peaks 10-12 though since they are aromatic.