A study of the carbon-halogen bond breaking in tert-butyl halides by the PM3 quantum chemical method

Abstract

Quantum chemical calculations by the semiempirical PM3 method are performed for halogen tert-butanes t -BuX (X = Cl, Br) and their radical anions in the gas phase and model polar solvent. It is shown that these radical 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 equilibrium one R 0 to R ≈ 2.2–2.3 A ̊ the potential curves for t -BuCl −. and t -BuBr −. may be well approximated by the exponential functions U f = B exp [−2 β ( R − R 0 )]. Activation energies and the values R ∗ for the transitional configuration for the reactions t -BuX + e → t -Bu . + X − in the gas phase are calculated.