Sydnone Ethylenes. II. Electronic Interactions in 4‐Styryl‐sydnonesAn estimation of intramolecular donor/acceptor interactions in 4‐styryl‐sydnones can be made by the substituent incrementsZtransderived from the corresponding vinyl compounds and by the comparison of the u.v.‐spectra of ω(E)‐substituted styrols. Because of the different anisotropic effects of sydnone and aryl groups the chemical shifts of the ethylene protons are not suitable for this purpose. The observed and calculated u.v.‐spectra show that the electronic excitation of 4‐styryl‐sydnones causes a strengthening of the sydnone donor effect and a decrease of the bond‐ord