MEAN AMPLITUDES OF VIBRATION FOR SOME CONJUGATED CARBONYL COMPOUNDS - GLYOXAL, ACROLEIN AND P-BENZOQUINONE

A normal-coordinate analysis has been carried out on the in-plane vibrations of three planar conjugated carbonyl compounds: glyoxal, acrolein andp-benzo-quinone. The derived force constants have been used to calculate the mean amplitudes of vibration. The results seem to be reliable inasmuch as the orders of magnitude are reasonable throughout, and great similarities are found for mean amplitudes of corresponding atom pairs in the three related molecules in question. For glyoxal and acrolein the results have been compared with mean amplitudes obtained by electron diffraction. For some of the distances substantial discrepancies were noticed. It is concluded that some of the reported electron-diffraction mean amplitudes seem to be doubtful. For the CO bond in particular the results of the present calculations give a characteristic value of 0.039 Å with negligible temperature variation from absolute zero to room temperature, and in satisfactory agreement with the electron-diffraction results. © 1969.