Study of the formamide–methanol dimer with ab initio and density functional theory methods

Abstract

ABSTRACT:For the first time, the structures and energies for the hydrogen bonding of a 1:1 complex formed between formamide and methanol molecules have been computed with various pure and hybrid density functional theory (DFT) and ab initio methods at varied basis set levels from 6-31g to 6-31ϩg(d,p). Five reasonable geometries on the potential energy surface of methanol and formamide system are considered and their relative stability is discussed. The infrared (IR) spectrum frequencies, IR intensities, and vibrational frequency shifts are reported. From the systematic studies, it is found that all the DFT methods selected here correctly compute the dimerization energies and geometries, with the B3P86 method predicting the hydrogen bond lengths relatively shorter and BPW91 yielding the interaction energies relatively lower. Finally, the solvent effects on the geometries of the formamide-methanol complexes have also been investigated using self-consistent reaction field (SCRF) calculations with five different DFT methods at the 6-31ϩg(d,p) basis set level. The results indicate that the polarity of the solvent has played an important role on the structures and relative stabilities of different isomers. Moreover, the basis set superposition error correction is critical to the interaction energies in the polar solvents.

Computational Study of Noncovalent Complexes between Formamide and Formic Acid

“…Four stable formamide-methanol (M-FMA) dimers have been studied by Fu various basis sets. 22 The two most stable M-FMA complexes have similar geometries compared to those of the FA-FMA and W-FMA dimers. MF I is a cyclic dimer with OH M ‚‚‚OdC FMA and NH FMA ‚‚‚O-H M interactions.…”

“…The presence of carbonyl groups in both FMA and FA results in additional stabilizations which do not exist in the water−formamide (W−FMA) and the methanol−formamide (M−FMA) complexes. Nevertheless, there are very interesting analogies among all the FMA complexes with water, methanol, and formic acid. ,, (Figure ).

2 B3LYP structures of FMA−water, FMA−methanol, and selected FMA−FA dimers.

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“…It is interesting to mention that for the FMA−water and FMA−methanol dimers the binding energy to the carbonyl group of FMA is slightly more favorable than to the amide group. ,, In the most stable FA−FMA dimer A both interactions are present, and the distance between the carbonyl oxygen atom of FMA and the hydroxyl hydrogen atom of FA is nearly 0.2 Å shorter than the hydrogen bond distance between the amide hydrogen atom of FMA and the carbonyl oxygen atom of FA (Figure ).…”

“…Four stable formamide−methanol (M−FMA) dimers have been studied by Fu et al using DFT and ab initio methods with various basis sets . The two most stable M−FMA complexes have similar geometries compared to those of the FA−FMA and W−FMA dimers.…”

“…In addition to their biological interest, they provide good models for studying the competition between noncovalent interactions involving nitrogen and oxygen atoms in the same molecule. As already mentioned, FA and FMA homodimers, as well as their complexes with other molecules like water and methanol, have been intensively studied. − However, only few reports are found about FA−FMA heterodimers. The computational study of the electron-density-dependent properties of FA, FMA, and their homo- and heterodimers made by Galvez et al, the crystallographic structure by Nahringbauer and Larsson in 1968, and the ab initio calculations of Neuheuser et al are of special interest.…”