The change in the H-1 and C-13 isotropic magnetic shielding constant of F3CH on formation of the H-bonded F3CH center dot center dot center dot Y complexes, Y = F-, Cl-, NH3, N(CD3)(3), FH, ClH, OH2, SH2, N-2, CO, OCO, Ar, NCH and O(CH3)(2), were determined by GIAO MP2 ab initio and DFT computations. A good correlation between the sign of frequency shift and the change of the proton magnetic shielding was obtained, i.e., red-shifted complexes show the characteristic downfield shift of the isotropic proton magnetic resonance while in blue-shifted complexes the resonance is shifted upfield or shifted downfield but to a much smaller extent than in red-shifted complexes. Similar results were obtained for the C-13 shifts. Counterpoise correction and basis set variation of the magnetic shielding were also considered. (c) 2007 Elsevier B.V. All rights reserved.