A STUDY OF THE CARBON-HALOGEN BOND BREAKING IN TERT-BUTYL HALIDES BY THE PM3 QUANTUM-CHEMICAL METHOD

Quantum chemical calculations by the semiempirical PM3 method are perf ormed for halogen tert-butanes t-BuX (X=Cl, Br) and their radical anio ns in the gas phase and model polar solvent. It is shown that these ra dical anions are unstable in polar solvents. Potential energy surfaces for t-BuBr(-.) and t-BuI(-.) have shallow minima in the gas phase. In the range of the values of the distances R(C-halogen) from the equili brium one R(0) to R approximate to 2.2-2.3 Angstrom the potential curv es for t-BuCl(-.) and t-BuBr(-.) may be well approximated by the expon ential functions U-f=B exp[-2 beta(R-R(0))]. Activation energies and t he values R for the transitional configuration for the reactions t-Bu X + e --> t-Bu(.) + X(-) in the gas phase are calculated.