MP2/6-31++G(d,p) and DFT B3LYP/6-31++G(d,p) calculations were performed of the structure, binding energies, and vibrational modes of complexes between dimethyl sulfoxide (DMSO) as a proton acceptor and monoprotic linear acids HX (X = F, Cl, CN) as well as monoprotic carboxylic acids HOOCR (R = -H, -CH3, -C6H5) in 1:1 and 1:2 stoichiometric ratios. The results show that two different structures are possible in the 1:2 ratio: in the first, the DMSO molecule interacts with both acid molecules (leading to a "Y" structure); in the second, the DMSO interacts with only one monoprotic acid. The second structure shows a lower stability per hydrogen bond. The spontaneities of the reactions to form the 1:1 and 1:2 complexes are greatly influenced by the X group of the linear acid. With the exception of HCN, all the reactions are spontaneous. In the 1:2 complexes with Y structure, we observed that the hydrogen atoms of the linear acid are coupled in symmetric and asymmetric modes, while this type of coupling is absent from the other 1:2 complexes.

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Theoretical calculations using both the second‐order Møller–Plesset and B3LYP levels of calculation with the 6‐31++G(d,p) and 6‐311++G(3df,3pd) basis sets were performed to determine stable structures, binding energies, and molecular properties for the H‐bonded complexes involving acetylene and formic acid. Three complexes were characterized as minima because no imaginary frequency was found. The calculations indicate that the most stable complex presents two H‐bonds forming a quasi‐cyclic structure. As expected, the HO stretching frequency of the formic acid is shifted downward after complexation, whereas its IR intensity is enormously increased. Finally, we have also studied the R1C2HHOOCR2 H‐bonded complexes with R1 and R2CH3 and C6H5 to compare their binding energies with that obtained to the HCOOHC2H2 complex. In this procedure, we have considered the most stable structure obtained to this latter using the B3LYP theoretical calculations with the 6‐31++G(d,p) basis set. © 2012 Wiley Periodicals, Inc.

Theoretical calculations 6-311++G(d,p) have been performed in order to obtain binding energies and molecular properties of complexes involving nitrous oxide ( N2O ) and two HX (X = F, Cl, Br and CN ) molecules. Our calculations have revealed the existence of eleven stable structures. The vibrational changes which take place in the HX acid after complexation follow the usual behavior: the HX stretching frequency is shifted downward whereas its IR intensity is much enhanced. The new vibrational modes arising upon H-bond formation, were verified, especially, those associated with the out-of-plane and in-plane HX bending modes, which are pure rotations in the HX isolated molecule.