The reaction mechanism of HF with HOBO is theoretically investigated. At the CCSD(T)/6-311++G(2d,2p)//MP2/ 6-311++G(d,p) level with zero-point energy correction two low-lying and three high-lying intermediates are found to be kinetically stable and should be isolated in experiments if available and accurate precursors or reactants are used. The primary reaction products of the reaction are suggested to be H2O and FBO, which are predicted to form through two multiple-step reaction channels with 46.64 and 43.88 kJ/mol initial reaction barrier, but not via a direct four-center transition state with a 118.39 kJ/mol energy barrier, which has been suggested in previous study. (C) 2003 Elsevier B.V. All rights reserved.