New NO-donors with antithrombotic and vasodilating activities, VII: Z/E-isomerism in thiazole- and 1,3,4-thiadiazole-2-nitrosimines.

In thiazole- (23 compounds) and 1,3,4-thiadiazole-2-nitrosimines (20 compounds) Z/E-isomers were described by 1H-NMR-spectroscopy. There is a mutual conversion of the isomers. The coalescence temp. (Tc) mostly is 310 K. In the thiazole series, however, for five compounds higher energy barriers are observed. This is due to substituents in 4-position with electron withdrawing properties. The Tc is increased when the compounds are dissolved in water instead of DMSO. Hereby it is concluded that the isomers have Ze or Ee configuration. It is made probable that the low field signal for the substituent in 3-position corresponds to the Ze-isomer, which has a slight preference. The free enthalpy of rotation, calculated approximately, is between 56.0 (1m) and 73.7 kJ/mol (1r).