Structures of some fluorinated benzenes determined by ab initio computation

The structures of fluorobenzene, 1,3-difluorobenzene, 1,3,5-trifluorobenzene, 1,2,3-trifluorobenzene, pentafluorobenzene, and hexafluorobenzene have been determined by the ab initio gradient method with a 4-21 basis set. Approximate corrections have been developed to yield r_e and r₀ structures so that comparison can be made with the available experimental information. The C? F bond distance decreases in a uniform manner with increasing fluorination of the ring, either on adjacent or on meta sites. The ring structure also shows systematic deformation, with a decrease of about 0.01 Å in the C? C bond length adjacent to the point of substitution and an increase of about 2.5? in the ring angle at the substitution site in those cases where the requirement of ring closure permits.