The molecular structure of benzene derivatives, part 2: 4-chloro-benzaldehyde by joint analysis of gas electron diffraction, microwave spectroscopy and ab initio molecular orbital calculations

The molecular structure of gaseous 4-chlorobenzaldehyde has been determined by a joint analysis of gas electron diffraction data, rotational constants from microwave spectroscopy, and constrained by results from ab initio calculations. The ab initio calculations have been performed at the HF/6-311G** level of theory. The planar C-s symmetry structure was found to be the only stable conformation. The torsion of the formyl group has been treated as a large amplitude motion. The most important structure parameters (r(g),) from the joint analysis with estimated total errors (in parentheses) are:(C-C)(mean) = 1.398(1)Angstrom, C-Cl = 1.734(3) Angstrom, C-C(= O)= 1.482(10) Angstrom, C = O = 1.216(5) Angstrom, (CCClC = 121.0(5)degrees, and (CCCHOC = 120.2(8)degrees. A scaled molecular force field has been determined. The ground state rotational constants have been determined from microwave data. (C) 1998 Elsevier Science B.V.