The C-H bond length change and the harmonic vibrational frequency shift of the C-H stretch on formation of the F3C-H center dot center dot center dot B (B = FH, ClH, OH2, SH2 and Cl-) complexes were determined by ab initio computations at the MP2/6-311+G(d,p) level of theory. They were found to agree with predictions from perturbation theory involving the first and second derivatives of the interaction energy with respect to displacement of the C-H bond length from its equilibrium value in the isolated F3C-H monomer. Blue shifts were obtained for all of the complexes, except F3CH center dot center dot center dot Cl- which has a large red shift. (c) 2006 Elsevier B.V. All rights reserved.