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A systematic approach to symmetry breaking in molecular calculations, based on MCSCF and multireference CI (MRCI) wave functions, is presented. A series of MCSCF expansions is generated by successively incorporating resonance effects and size effects into the wave functions. The character of the potential surface obtained at each level is analyzed. As an example, the potential energy curves of the ground state (σ) and the first excited state (π) of the formyloxyl radical (HCO2) are characterized. The σ and π equilibrium structures are shown to be symmetric, with an adiabatic σ−π excitation energy of 9.2 kcal/mol. Unlike earlier theoretical studies, our MCSCF model produces a qualitatively correct potential surface. Therefore, we are able to extract reliable vibrational frequencies from the MRCI potential surface.

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tn; benzene, 25°) afforded the aminothiones10 4 and 5 (60-80%), which proved susceptible to ring closure by further condensation. Reaction of 4 with en (2 equiv), tn (2 equiv), and tn (6 equiv) in benzene (70°, 1 hr) yielded after separation from by-products the macrocycles 6 (40%, mp 286-289°), 711 (--'30 %, mp 220-222°), and 8 (30%, mp 147-148°), respectively, as white solids from chloroform-ethanol. Macrocycle 8 is better obtained from 5 and tn (2.5 equiv, benzene, 70°); yields of 90% have been achieved by this route.12 Molecular weights of 6-8 were confirmed by highresolution mass spectra (e.g., calcd for 12C241H2814N4

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