The molecular structure and benzene ring distortions of ethynylbenzene have been investigated by gas-phase electron diffraction and ab initio MO calculations at the HF/6-31G* and 6-3G** levels. Least-squares refinement of a model with C2v, symmetry, with constraints from the MO calculations, yielded the following important bond distances and angles:rg(Ci-Co)=1.407±0.003 Å, rg(Co-Cm)=1.397±0.003 Å, rg(Cm-Cp)=1.400±0.003 Å, rg(Cri-CCH)=1.436 ±0.004 Å, rg(C=C)=1.205±0.005 Å, ∠Co-Ci-Co=119.8±0.4°. The deformation of the benzene ring of ethynylbenzene given by the MO calculations, including <Co-Ci-Co=119.4°, is insensitive to the basis set used and agrees with that obtained by low-temperature X-ray crystallography for the phenylethynyl fragment, C6H5-C≡C-, in two different crystal environments. The partial substitution structure of ethynylbenzene from microwave spectroscopy is shown to be inaccurate in the ipso region of the benzene ring.
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry