R. Dutler

The structure of bicyclo[2.2.1]heptanes: Norbornane, nornornene, norbornadiene, 7-oxanorbornane, and 7-thianorbornane

Abstract The structures of norbornane, norbornene, norbornadiene, 7-oxanorbornane, and 7-thianorbornane were completely determined by analytical gradient techniques in conjunction with ab initio Hartree—Fock molecular orbital theory. Geometric details obtained at the minimal STO-3G and split valence 3–21G levels of theory, are compared with data available from various experimental studies using both microwave and electron diffraction spectroscopy. Variations in the geometric parameters which ensue from introduction of the functional groups into the bicyclo [2.2.1] heptane skeleton are discussed in terms of perturbative molecular orbital (PMO) theory.

The vibrational spectra (100–1600 cm−1) and scaled abinitio STO‐3G and 3‐21G harmonic force fields for norbornane, norbornene, and norbornadiene

The vibrational spectra in the region of 100–1600 cm−1 of norbornane and norbornadiene are reinvestigated, and those of norbornene reported for the first time. On the basis of 3‐21G ab initio force fields, evaluated for each molecule and scaled using overlay refinements of 12 scaling factors, the spectra are assigned and the observed transition frequencies reproduced with an overall average error of 6.2 cm−1. STO‐3G force constants, modified to correct for deficiencies in the stretch/bend interaction force constants but otherwise scaled analogously to 3‐21G, reproduce the final set of assignments to within 10.1 cm−1 on average. The STO‐3G basis is shown to be suitable as a less costly alternative to split‐valence basis sets, particularly for describing the vibrational dynamics of low frequency ring bending and torsional modes.