Blue and red shifts in F3C–H ⋯ B (B = FH, ClH, OH2, SH2 and Cl−) complexes predicted by a perturbative model

The C–H bond length change and the harmonic vibrational frequency shift of the C–H stretch on formation of the F3C–H ⋯ 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 ⋯ Cl− which has a large red shift.