Microwave Spectrum of Bromobenzene, Its Structure, Quadrupole Coupling Constants, and Carbon—Bromine Bond

As part of a study of the effects of substitution in the benzene ring, an experimental investigation of the microwave spectrum of bromobenzene has been carried out. The spectrum of four isotopically substituted molecular species of bromobenzene have been obtained: C6H579Br, C6H581Br, C6D579Br, and C6D581Br. Rotational and quadrupole coupling constants were obtained in each case. The number of experimental rotational constants obtained was insufficient to permit a determination of the structure of the molecule without additional assumptions. The following structure is obtained for bromobenzene if hexagonal symmetry of the ring is arbitrarily assumed: rC–C1.4020 Å;rC–H1.0698 Å;rC–Br1.8674 Å. The quadrupole coupling data for these molecules are consistent with a value of 1%—2% double-bond character for the C–Br bond.