13C N.M.R. spectra of I, II, III, IV and V have been measured and a number of important assignments made. The resulting chemical shifts are correlated with calculated charge densities. Compound IV has been compared with the tetraphenylcyclobutadiene dication in the literature.
Hout-Lodder, van der, A. E., Haan, de, J. W., Ven, van de, L. J. M., & Buck, H. M. (1973). 13C N.M.R. and charge distribution in arylcyclobutenyl cations. Part II. Recueil des Travaux Chimiques des Pays-Bas, 92(9), 1040-1046. https://doi.org/10.1002/recl.19730920914