The first part of this paper shows how the ordinary Born-Oppenheimer approximation for separating nuclear and electronic motion can be adapted to a degenerate electronic state. To set up equations of motion for the dynamical Jahn-Teller effect in their simplest form we use vibrational amplitudes associated with special linear combinations of the degenerate electronic wave functions, chosen to vary as slowly as possible with nuclear displacements. We also discuss briefly the symmetry-forbidden electronic transitions allowed by a Jahn-Teller distortion. In the second we make molecular orbital calculations of the energies and distorted shapes of some aromatic hydrocarbon molecules. The differences in energy between the distorted and symmetrical shapes (in kcal/mole) are cyclobutadiene 11.43; cyclopentadienyl 1.414, cycloheptatrienyl 0.859; benzene negative ion 1.077; triphenylene and coronene negative ions 0.385 and 0.299. In the last three each shape of minimum energy is separated from two equivalent ones by a small potential barrier, respectively, 0.000, 0.001, and 0.002. The ground state of each radical is doubly degenerate, and it can oscillate about a continuous series of distorted shapes. In the excited 1E1u+ and 3E1u+ states of benzene the distortions are much smaller, and the CC bonds probably bend rather than stretch.

The pseudo-Jahn—Teller effect, the vibronic interaction of nearly degenerate electronic states, arises in the same manner as the Jahn—Teller effect itself. An iteration method, suitable for desk calculation, has been developed to allow computation of the vibronic wavefunctions and energies of a system with two closely spaced electronic states. A calculation on benzene anion compares favorably with previously published results. The method, in combination with semiempirical evaluation of the necessary parameters, has been applied to various substituted benzene anions and the ESR spectra of these anions predicted. The results compare satisfactorily with experiment and indicate that the spectra are the net result of three principal factors, configuration interaction among the simple molecular orbital electronic states, vibronic coupling, and thermal equilibrium between at least two vibronic states.

The acylation of 3-carbalkoxycitraconic esters 1 with amide acetals provides a good method for the synthesis of dimethylaminoalkylidene malonates 3; these compounds upon treatment with a primary amine cyclize to 2,3dicarbalkoxy 6-substituted 2(lH)-pyridones 4. Application of this reaction to the acetal or imminium salt from o-cyanoarylamides 9a,b similarly affords the corresponding enamines 3d,e; hydrogenation of 3 leads directly to the fused pyridones 11 and 13, a potential camptothecin intermediate.

In dealing theoretically with the effects of vibronic interactions in substituted benzene mononegative radical-ions it is useful to know the spin density distributions in the degenerate ground level of unsubstituted benzene anions. A configuration interaction theory is developed for hydrocarbon anions with degenerate ground states and applied to the benzene anion problem. The results show negative spin densities on atoms having zero spin density in the Htickel approximation.