4-DIHYDRO-2H-PYRAN, 3,6-DIHYDRO-2H-PYRAN, 2,3-DIHYDRO-1,4-DIOXIN, AND 4H-1,3-DIOXIN VIBRATIONAL POTENTIAL-ENERGY SURFACES OF 3

The far-infrared and Raman spectra of several oxygen analogues of cyclohexene have been reported. The data have been reanalyzed for each molecule in terms of two-dimensional vibrational potential energy surfaces for the ring-bending and ring-twisting vibrations. Kinetic energy functions for each vibration were determined using vectorial methods. Coefficients for quartic-quadratic potential energy functions with fourth-order cross terms were calculated. In each case, the twisted (half-chair) conformation has the lowest energy. The bent (boat) conformations were determined to be saddle points in the surfaces with energies 3120 to 3830 cm1(37.2 to 45.6 kJ/mol) above the energy minima. The barriers to planarity range from 3500 to 4130 cm1(41.8 to 49.4 kJ/mol). The angles determined for the twisting of the ring are in satisfactory agreement with microwave results. 1989, American Chemical Society. All rights reserved.

VIBRATIONAL POTENTIAL-ENERGY SURFACES OF 3,4-DIHYDRO-2H-PYRAN, 3,6-DIHYDRO-2H-PYRAN, 2,3-DIHYDRO-1,4-DIOXIN, AND 4H-1,3-DIOXIN Academic Article