A matrix isolation study of the benzene bromine atom complex

Spectral Evidence of Bevel-Gear-Type Rotation of Benzene around Br in Solid p-H2: Infrared Spectrum of the C6H6Br Radical

Whether the structure of C₆H₆X (X = halogen), an intermediate in the halogenation of benzene, is an open or a bridged form has been debated. We produced Br to react with C₆H₆ upon photolysis in situ of a Br₂/C₆H₆/p-H₂ matrix at 3.2 K. In contrast to the C₆H₆Cl σ-complex reported previously, the observed infrared spectrum indicates that C₆H₆Br is an open-form π-complex. Furthermore, lines of the two CH out-of-plane bending modes associated mainly with even- and odd-numbered carbons, predicted near 672 and 719 cm^-1, merged into a broad line at 697.3 cm^-1, indicating that these modes become nearly equivalent as Br migrates from one carbon atom to another. Quantum-chemical calculations support that the benzene ring performs a bevel-gear-type rotation with respect to Br. Observation of only trans-ortho- and trans-para-C₆H₆Br₂ suggests that this gear-type motion allows the additional Br atom to attack C₆H₆Br only from the opposite side of the Br atom in C₆H₆Br.

V, Nb, and Ta Complexes with Benzene in Solid Argon: An Infrared Spectroscopic and Density Functional Study

Vanadium, niobium, and tantalum metal atoms, produced by laser ablation, are reacted with benzene vapor diluted in argon and codeposited onto a 7 K CsI window. The resulting reaction products are trapped, and the M(C6H6) and M(C6H6)2 complexes are identified by benzene isotopic substitution (C6H6, 13C6H6, C6D6). Density functional theory (DFT) frequency calculations are used to support molecular complex assignments. On the basis of the computed energies and a comparison of calculated and observed vibrational isotopic shifts, the ground electronic states and geometries are predicted. The bonding and electronic interactions in these molecules are discussed on the basis of the observed aromatic C-C breathing modes activated in the complexes.

Computational study of the halogen atom-benzene complexes

The structures of halogen atom-benzene complexes were investigated by modern DFT and ab initio computational methods. The spectroscopic properties of the complexes are also predicted and are in good agreement with experiment where such data have been reported. The fluorine atom-benzene complex is predicted to be a sigma complex due to the strength of a C-F bond. The chlorine atom-benzene complex is predicted to have an eta(1) pi complex structure, which is only slightly more favorable (1.1 kcal/mol with the BH&HLYP/6-311++G method including the ZPE correction) than a sigma complex but is significantly more stable (4.4 kcal/mol with the BH&HLYP/6-311++G method including the ZPE correction) than the eta(6) pi complex. The bromine and iodine benzene complexes are also predicted to prefer an eta(1) pi complex structure.