Far-infrared spectra and ring--puckering potential energy function of 4H-pyran. Conformations and bonding of 1,4-cyclohexadiene and its oxygen analogs Academic Article uri icon

abstract

  • The far-infrared, mid-infrared, and Raman spectra of 4H-pyran have been recorded and analyzed. The far-infrared gas-phase spectrum of this molecule shows a series of 12 bands between 115 and 128 cm−1 arising from the ring-puckering vibration. The kinetic energy (reciprocal reduced mass) expansion was calculated for this mode and utilized in the determination of the potential energy function, which was found to be V (cm−1) = (1.21 × 105)x4 + (2.24 × 104)x2, where χ is the ring-puckering coordinate in angstroms. This shows the ring to be planar. The corresponding potential energy functions for the analogous 1,4-cyclohexadiene and 1,4-dioxin are respectively nearly harmonic and nearly quartic. Molecular mechanics (MM3) calculations satisfactorily reproduce the 1,4-cyclohexadiene potential function but underestimate the torsional forces of the C=C-O-C system in the oxygen analogues. In fact, 1,4-dioxin is incorrectly predicted to have a boat configuration. It is shown that weak π interactions between the C=C bonds and the nonbonded oxygen orbitals account for the increases in the torsional forces and the resulting potential functions. © 1993, American Chemical Society. All rights reserved.

author list (cited authors)

  • Choo, J., Laane, J., Majors, R., & Villarreal, J. R

complete list of authors

  • Choo, J||Laane, J||Majors, R||Villarreal, JR

publication date

  • January 1, 1993 11:11 AM