Analysis of A2B2 NMR Spectra. II. Nonsymmetrical 1,2-Disubstituted Ethanes

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Abstract
The features of A2B2 proton magnetic resonance spectra of nonsymmetrical 1,2‐disubstituted ethanes are discussed in detail. It s shown that under certain conditions the magnitudes and signs of all the coupling constants may be obtained for this type of A2B2 spectra. Typical calculated spectra along with several experimental spectra are given to illustrate these conditions. With one exception, experimental data are given only for molecules for which all four of the coupling constants are obtained. It is found that the geminal coupling constants are of opposite sign from the rotationally averaged values for the vicinal couplings. The values of the geminal couplings are approximately those found by other workers in the corresponding monosubstituted methanes. Small vicinal substituent effects on the geminal coupling constants are reported for several of the substituent groups. Assignment of the chemical shift of the particular methylene group is based on the comparison of the A2B2 chemical shifts with the chemical shifts in the related ethyl compounds.

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