REDUCED MASS CALCULATIONS, LOW-FREQUENCY VIBRATIONS, AND CONFORMATIONS OF 1,4-CYCLOHEXADIENE, 1,4-DIOXACYCLOHEXADIENE-2,5, AND 9,10-DIHYDROANTHRACENE
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abstract
Vector-based computer programs have been written in order to calculate the kinetic energy (reciprocal reduced mass) expansions as a function of the coordinate for the ring-puckering, ring-twisting (in-phase), and ring-twisting (out-of-phase) vibrations of 9,10-dihydroanthracene. The same programs also permit the kinetic energy expansions for all three vibrations to be calculated for smaller molecules including 1,4-cyclohexadiene and 1,4-dioxacyclohexadiene-2,5. The reduced mass calculated for the ring-puckering vibration of 1,4-cyclohexadiene has a minimum value for the planar conformation and increases substantially as the molecule puckers. The kinetic energy expansion for this vibration, used along with a harmonic ring-puckering potential energy function, quantitatively accounts for the observed far-infrared spectrum. This molecule is thus clearly planar. The potential energy function for 1,4-cyclohexadiene calculated from a molecular mechanics program does a remarkable job in predicting the ring-puckering frequencies when the calculated reduced mass expansion is used. The kinetic energy expansions for the puckering and twisting vibrations of 1,4-dioxacyclohexadiene-2,5 and 9,10-dihydroanthracene have also been used in conjunction with potential functions to help analyze the observed spectra for these molecules. 1988.
