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The possibility of 1,3-orbital overlap stabilization in the 1,3-diphenylcyclobutenyl cation (3) is explored by comparison of the nmr spectra of cycloalkenyl cations 1-4. It is concluded that 1,3-electrostatic repulsion results in charge dispersion in cation 3. Extensive charge dispersion onto the phenyls in diphenylcyclopropenium ion (4) is found, accompanied by an unusually low barrier to rotation in accord with extended Hückel calculations.Several useful syntheses of cyclobutane and cyclobutene derivatives are described.

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The Johnson-Bovey-Waugh-Fessenden double-loop model for the ring-current effect in the nmr spectra of aromatic systems is compared with a slightly less arbitrary double-toroidal shell model. The calculated effect for all points greater than 3 A from the center of the ring is nearly the same for the two models. At closer distances, significant differences sometimes arise. The double-toroidal shell model is used to calculate the ringcurrent effect in the nmr spectra of diand triphenylcyclopropenium ions at different angles of twist of the phenyl groups from coplanarity. Comparison with observed spectra gives a self-consistent picture at twist angles from 9.5 to 13.5°. The charge distribution in the ions is discussed briefly.