A Proton Nuclear Magnetic Resonance Study of the Exchange Reactions of Acetonitrile – Boron Trihalide Adducts with Excess Acetonitrile

Proton n.m.r. studies of the mechanism for exchange of excess acetonitrile with CH3CN•BX3 (X = F, Cl, Br) adducts show that the rates and activation energy for dissociation are influenced by solvent effects when mixed solvents such as C6H5NO2/CH2Cl2 or CD3NO2/CH2Cl2 are used. On extrapolation to inert solvent conditions, first order activation energies are obtained which are in close agreement with previously measured dissociation energies of acetonitrile adducts in solution. The relative rates of dissociation are CH3CN•BF3 > CH3CN•BCl3 > CH3CN•BBr3; in agreement with previous experimental evidence that the strength of the donor–acceptor band varies as CH3CN•BBr3 > CH3CN•BCl3 > CH3CN•BF3.