Molecular Vibrations of Quinones. V. Normal Coordinate Analysis of p-Benzoquinone and Its Isotopic Derivatives

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Abstract
The frequencies of the normal vibrations of ordinary, monodeutero‐, 2,5‐dideutero‐, 2,6‐dideutero‐, and tetradeutero‐p‐benzoquinone as well as ordinary and tetradeutero‐p‐benzoquinone‐18O2 have been calculated by using a quadratic potential function of the valence‐force field type with all the important cross terms. For the out‐of‐plane vibrations, Anno and Sadô's force constants have been used. For the planar vibrations, two sets of force constants have been tried. One of the sets was obtained from the force constants in benzene, hexafluorobenzene and ethylene with proper considerations and modifications. In the second set, the diagonal and off‐diagonal constants among the CC and the CO stretches have been obtained by the method of Coulson and Longuet‐Higgins, the other constants being the same as in the first set. Further calculations have been tried in order to improve the results by adjusting a few of the force constants in such a way that some of the frequencies well established by experiment are reproduced by the calculation. Only the results for ordinary and tetradeutero‐p‐benzoquinone are given in the present paper; the results for other isotopic quinones are tabulated in Part VI of this series, in which the assignment of vibrational frequencies to modes of vibrations is discussed.

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