Some Sample Spectra—Equivalent Carbons

Through the mathematical manipulation of the results of each of the different DEPT pulse sequences, it is also possible to present the results as a series of subspectra in which only the CH carbons appear in one trace, only the CH2 carbons appear in the second trace, and only the CH3 carbons appear in the third trace. Another eommon means of displaying DEPT results is to show only the result of the DEPT-135 experiment. The spectroscopist generally can interpret the results of this spectram by applying knowledge of likely chemical shift differences to distinguish between CH and CH3 carbons. 

The results of DEPT experiments may be used from time to time in this textbook to help you solve assigned exercises. In an effort to save spaee, most often only the results of the DEPT experiment, rather than the complete spectrum, will be provided. 

Although this compound has a total of six carbons, there are only four peaks in the NMR spec- 

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A carbon attached to a double bond is deshielded due to its sp hybridization and some diamagnetic anisotropy. This effect can be seen in the NMR spectrum of cyclohexene (Fig. 6.12). Cyclohexene has a plane of symmetry that runs perpendicular to the double bond. As a result, we observe only three absorption peaks. There are two of each type of carbon. Each of the double-bond carbons c has only one hydrogen, whereas each of the remaining carbons has two. As a result of a reduced NOE, the double-bond carbons have a lower-intensity peak in the spectrum. 

6 carbon atoms appear in the spectrum. Unique carbon atoms indicated with a dot. 

172 ppm has already been labeled as arising from the carbonyl carbon at 6. This peak appears only in the original spectrum therefore, it must not have any attached hydrogens. 

Equivalent atoms appear at the same chemical shift value. Frgure 4.10 shows the proton-decoupled carbon spectrum for 2,2-dimethylbutane. The three methyl groups at the left side of the molecule are equivalent by synunetry. 

Nuclear Magnetic Resonance Spectroscopy Part Two Carbon-13 Spectra 

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