N.M.R. SPECTRA OF SOME α–β UNSATURATED ESTERS

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Abstract
The results of analysis of methyl citraconate and mesaconate, methyl cis- and trans-crotonate, and methyl cis- and trans-2-pentenoate are reported. A previously reported analysis of the crotonates by first-order perturbation theory gave significantly different values for the 1,3 coupling constants. The discrepancy in results, which is due to the importance of second-order effects, emphasizes the need for caution in applying the first-order method. From values of 1,3 coupling constants reported here and elsewhere it is concluded that there is no simple relation between the magnitude of 1,3 coupling constants and geometrical configuration of the interacting nuclei.