THE MOLECULAR-STRUCTURE OF BENZENE-DERIVATIVES .1. 4-FLUOROBENZALDEHYDE BY JOINT ANALYSIS OF GAS ELECTRON-DIFFRACTION, MICROWAVE SPECTROSCOPY AND AB-INITIO MOLECULAR-ORBITAL CALCULATIONS

The molecular structure of gaseous 4-fluorobenzaldehyde has been deter mined by a joint analysis of gas electron diffraction data, rotational constants from microwave spectroscopy, and constrained by results fro m ab initio calculations. The ab initio calculations have been perform ed at the HF/6-311G* and MP2/6-31G* levels of theory. The planar C-s symmetry structure was found to be the only stable conformation. The t orsion of the formyl group has been treated as a large-amplitude motio n. The most important structure parameters (r(g)) from the joint analy sis with estimates of 2 sigma (in parentheses) were: (C-C)(mean) = 1.3 97(1) Angstrom, C-F = 1.331(7) Angstrom, C-C(=O) = 1.488(7) Angstrom, C-O = 1.195(5) Angstrom, <CCFC = 122.3(2)degrees, and <CCCOHC = 121.3( 7)degrees. A scaled molecular force field has been determined. (C) 199 7 Elsevier Science B.V.