Statistical Theory of Hindered Rotation in Molecular Crystals, II

Dissecting the hindered rotation of ethane.

The existence of a rotational barrier of ca. 3 kcalmol 1 around the C C single bond in ethane has been known since the early studies of Ebert, Wagner, Eucken and Weigert and Pitzer done in the 1930s. Even the simplest ab initio methods are able to reproduce this fundamental result. However, the physical origin of this hindered rotation is still under controversy in the literature. There are two...

The Molecular Symmetry Group Theory for Trimethylamine-BH3 Addend(BH3 Free of Rotation)

Hindered rotation in ion-neutral molecular complexes: The n1 vibration of H2–HCO

Infrared spectra of the mass selected ionic complexes H2–HCO 1 and D2–DCO 1 have been recorded in the vicinity of their n1 vibrations ~H2 /D2 stretch! by means of photofragmentation spectroscopy. The anomalous rotational constants obtained by fitting the observed line positions to a semirigid Watson A-type Hamiltonian reflect the appreciable zero-point excursions of the H2 /D2 molecule. Barrier...

Hindered Internal Rotations in Van der Waals Molecules and Molecular Crystals

The quantum dynamical behavior of the Van der Waals molecule (N& and that of the ordered a and y phases of solid N2 have recently been calculated, starting from the same ab initio Nz-Nz potential. By interpreting the results of these calculations we try to improve our understanding of the librationlinternal rotation motions of the N2 monomers and the orientational order-disorder (a-p) phase tra...

Hindered rotation in N-methylformamide. A peptide-bond model system.

Barriers to rotation about the C-N bond in the cis and trans isomers of N-methylformamide have been determined by n.m.r. spectroscopy. Representative values are 20.7 and 22.0 kcal/mole. Arrhenius parameters have also been determined. These results are compared with C-N barriers for N,N-dimethylformamide and unsubstituted formamide. The data suggest that C-N rotational barriers for N-methyl amid...