ISOMERIC EQUILIBRIA OF 1-METHYLAMINO-2-NITROETHENE

The solvent and concentration dependence of the isomeric equilibria of 1-methylamino-2-nitroethene were studied by H-1 and C-13 NMR spectros copy. The results are used for clarification of the controversy regard ing the content of the E form in CDCl3 solution, correcting an earlier suggestion concerning the stereochemical assignments around the C-1-N bond in the E form and verification of the values of the olefinic one bond proton-carbon spin-spin coupling constants, (1)J(C,H), reported recently. An unambiguous means of assigning the stereochemistry around the C-1-N bond in the E isomer is suggested, based on using the compl ementary information from (3)J(C-2,NH) and (3)J(H-1,NH), in addition t o the (3)J(Me,H-1) vicinal coupling constant.