The hydrogen bonding of 1:1 complexes formed between formamide and methanol has been investigated using DFT and MP2 methods at varied basis set levels from 6-31g to 6-31 ++g(2d, 2p). Five reasonable geometries are considered with the global minimum being a cyclic double-hydrogen bonded structure. The IR intensities and vibrational frequency shifts are reported. The solvent effects on the geometries of the complex have also been investigated using SCRF calculations at the B3LYP/6-31 +g(d, p) level. The results indicate the polarity of the solvent has played an important role on the structures and the relative stabilities of different isomers. (C) 2003 Elsevier B.V. All rights reserved.