Glenn H. Penner

A molecular orbit study of the barrier height in benzaldehyde, and the changes in geometry which accompany the rotation of the formyl group

Abstract The basis set dependence of the barrier for internal rotation of benzaldehyde has been investigated at the STO-3G, 4-21G, 4-31G, 6-31G and 6-31G*(5D) levels of computation, employing complete geometry optimization at the higher levels. The torsional potential energy curves are fitted to the function. The STO-3G basis set gives the closest agreement with experiment for the barrier height V 2 . Split-valence basis sets give much higher values, e.g. ≈15kJ mol −1 greater than experiment with 6-31G*(5D). The changes in geometry induced by including polarization functions and those which accompany the rotation of the formyl group are discussed and compared with corresponding data for phenol.

Calculations of the C(1)C(α) torsional barrier in styrene. Comparison with experiment

Abstract Computations of the geometry optimized conformational energies of styrene at the STO 3G, 4–21G, and 4–31G levels of molecular orbital theory, bear out vibronic level fluorescence spectra showing a large fourfold component for the internal torsional potential function.

Ab initio MO calculations on structures and internal rotational barriers of nitroethene and nitrobenzene

Abstract The geometry of nitroethene is optimized at the STO-3G, 4-21G, 4-31G, 6-31G and 6-31G** levels of molecular orbital theory. The geometry of nitrobenzene is optimized at the STO-3G level. These ground state geometries are compared with those deduced from microwave experiments. The potential curves for nitro group rotation have been calculated for nitroethene and nitrobenzene. For nitroethene the curve deduced from torsional frequencies in the far infrared is very well reproduced by the STO-3G calculations. Two-fold barriers obtained from the torsional frequency in nitrobenzene are smaller than the calculated barrier, possibly due to the presence of a negative four-fold component in the potential function.

STO 3G MO computations of six-fold barriers in some toluene derivatives

Abstract STO 3G MO computations with geometry optimization of six-fold internal rotational barriers in toluene derivatives, 2,6-diX-C6H4CR3 (X = H, F, R = H, F, Cl, CH3 and X = Cl, R = H, F), are reported. The barrier magnitudes are as large as 9.5 kJ mol−1 for X = F, R = CH3. Inclusions of a twelve-fold potential in a fit of the computed energies yields significant values only for X = F, R = CH3, F. For all but R = F, the conformation of lowest energy has a CR bond lying in the benzene plane.

The STO 3G MO structure and internal rotational potential of benzophenone

Extensive geometry‐optimized STO 3G MO computations yield C2 symmetry and 32° for the twist angles of the phenyl groups in benzophenone. For the planar molecule the internal rotational barrier is 33.7 kJ/mol and is 24.6 kJ/mol for a twist angle of 90°. The expectation value of the twist angle is therefore very near 32° at 298 K; implying that, in the crystal, packing forces cause only a minor perturbation of the conformation, the angle being 30° in the solid. An energy profile for non‐C2 symmetry is also computed.