Bromine and Mixed Bromine Chlorine Oxides: Wave Function (CCSD(T) and MP2) versus Density Functional Theory (B3LYP) Calculations

Theoretical investigation of halogen-oxygen bonding and its implications in halogen chemistry and reactivity

Trends in the properties of normal valent and multivalent halogen-oxygen bonding are examined for the isomers of the halogen polyoxide families of the types (YXO2) and (YXO3), Y = Cl, Br, I, H, CH₃, X = Cl, Br, I. A qualitative model is formulated on the relationship between the X−O bond distance variations, the ionic character of the bonding, and the degree of halogen valence. The relative stability and enthalpy of formation of each species are also suggested to correlate with the ionic nature of the X−O bonding and the electrostatic character of the Y, YO fragments. In the model presented, halogen hypervalence is interpreted to be the result of partial p → d promotion of lone-pair valence electrons followed by the formation of two, four, or six additional pd hybrid bonds around the halogen atom.

The Br—O bond in halogen oxides — Empirical force constants and electronic characteristics

A number of bromine oxides and mixed chlorine–bromine oxides for which spectroscopic information is available have been chosen to investigate the nature and characteristics of the Br—O bond. The study consists of the empirical determination of stretching force constants for these bonds from observed vibrational spectroscopic data and the analysis of the topological characteristics of the bonds via ab initio calculations. The latter have been performed at the MP2 level with a 6-311+G(2df) basis set, to provide a uniform and systematic framework for comparing these species. Three types of Br—O bonds have been found, with different characteristics of strength and electron density. The results are compared with those recently found for the Cl—O bond in chlorine oxides.Key words: bromine oxides, bond electronic structure.

Quasiclassical trajectory studies on the gas-phase BrO self-reaction

The effect of initial vibrational energy and the mode of disposal of available energy into products for the disproportionation reaction between BrO radicals are studied using the quasiclassical trajectory (QCT) technique. The calculations are performed on an analytical potential enegy surface based on ab initio results reported for the three isomeric forms of (BrO)2 system. The results indicate a mild dependence on reactant vibrational energy, which is discussed in terms of the mechanistic aspects of the reaction. The study of the distribution of total accessible energy among products indicates a different mode of energy disposal in each path and hence important differences on the mechanism by which each channel takes place.