[Robert D5265]

Cyclohexanone has 4 unique signals in its C-13 NMR (See the reference). The signals are at 211.0 ppm (carbon 1), carbonyl carbon, 42. ppm, carbon 2 adjacent to carbon 1, 27.2 ppm, carbon 3, and 25.2 ppm, for carbon 4. Once again see the first reference for the structure of cyclohexanone and the chemical shifts of the molecule. The order involves the progression from C-4 to C-1. As you approach the carbonyl carbon the chemical shift of the carbon atoms in the ring become more deshielded because of the effect of the very electronegative O atom on the carbonyl carbon.Adipic acid has the structure shown below. The symmetrical nature of the molecule indicates it will have just a few unique carbon-13 signals. Expect one quite downfield peak at around 175 ppm due to the carboxyl carbon. Expect two more unique C signals similar to the 3 cyclohexanone signals from carbons farther away from the carboxyl group. The C atom closer to the carboxyl group will have a peak at around 33 ppm while the other unique C atom will yield a peak at about 24 ppm. The order of the chemical shifts in both molecules is seen to be that those farther away from the oxygen atoms have the farthest shift downfield while those other carbon peaks are less deshielded depending on how close they are to the carbonyl or carboxyl group carbon. Farther away means more shielded.Hope this makes sense. If you look at the referenced sites you should have a better idea of what I have said.......O..............................O......| |...............................||HO-C-CH2-CH2-CH2-CH2-C-OH

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