Carbon‐13 n.m.r. study of 31 P 13 C spin–spin coupling constants in dichloro‐ and monochloro‐vinyl phosphate derivatives

Carbon‐13 chemical shifts and J (PC) coupling constants of 29 vinyl phosphate derivatives are presented. In the series of compounds (R 1 O) 2 P(O)OC 1 (R   2 3 )C 2 X 2 (where 3 in R   2 3indicates the first carbon of the R 2 substituent) large differences were found between the 3 J (P, O, C‐1, C‐3) and 3 J (P, O, C‐1, C‐2) coupling constants of the chlorinated (XCI) and the unsubstituted (XH) derivatives. A possible explanation of this phenomenon is given on the basis of Jameson's s bond character theory. Strong stereospecificity of 3 J (P, O, C‐1, C‐3) coupling constants was observed in the series of compounds (R 1 O) 2 P(O)OC 1 (R   2 3 )C 2 HR 3 . Coupling constants varied between 3.2–4.9 Hz in the E isomers, while peaks could not be resolved in the Z isomers. The 3 J (P, O, C‐1, C‐2) coupling constants were regularly 20–30% greater in the Z than in the E isomers.