Theoretical influence of third molecule on reaction channels of weakly bound complex CO2… HF systems

Abstract

AbstractIn this investigation, reaction channels of weakly bound complexes CO2…HF, CO2…HF…NH3, CO2…HF…H2O and CO2…HF…CH3OH systems were established at the B3LYP/6‐311++G(3df,2pd) level, using the Gaussian 98 program. The conformers of syn‐fluoroformic acid or syn‐fluoroformic acid plus a third molecule (NH3, H2O, or CH3OH) were found to be more stable than the conformers of the related anti‐fluoroformic acid or anti‐fluoroformic acid plus a third molecule (NH3, H2O, or CH3OH). However, the weakly bound complexes were found to be more stable than either the related syn‐ and anti‐type fluoroformic acid or the acid plus third molecule (NH3, H2O, or CH3OH) conformers. They decomposed into CO2 + HF, CO2 + NH4F, CO2 + H3OF or CO2 + (CH3)OH2F combined molecular systems. The weakly bound complexes have four reaction channels, each of which includes weakly bound complexes and related systems. Moreover, each reaction channel includes two transition state structures. The transition state between the weakly bound complex and anti‐fluoroformic acid type structure (T13) is significantly larger than that of internal rotation (T23) between the syn‐ and anti‐FCO2H (or FCO2H…NH3, FCO2H…H2O, or FCO2H…CH3OH) structures. However, adding the third molecule NH3, H2O, or CH3OH can significantly reduce the activation energy of T13. The catalytic strengths of the third molecules are predicted to follow the order H2O < NH3 < CH3OH. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006