Theoretical study of the effects of substitution solvation and structure on the interaction between nitriles and methanol

Abstract

We report an investigation on intermolecular interactions in RACNHAOCH3 (R ¼ H, CH3, F, Cl, NO2, OH, SH, SCH3, CHO, COCH3, CH2Cl, CH2F, CH2OH, CH2COOH, CF3, SCOCH3, SCF3, OCHF2, CH2CF3, CH2OCH3, and CH2CH2OH) complexes using density functional theory. The calculations were conducted on B3LYP/6-311þþG** level of theory for optimization of geometries of complexes and monomers. An improper hydrogen bonding (HB) in the H3COAHNCAR complexes was observed in that N atom of the nitriles functions acts as a proton acceptor. Furthermore, quantum theory of ‘‘Atoms in Molecules’’ (AIM) and natural bond orbital (NBO) method were applied to analyze H-bond interactions in respective complexes. The electron density (q) and Laplacian (!2 q) properties, estimated by atoms in molecules calculations, indicate that HN bond possesses low q and positive !2 q values, which are in agreement with partially covalent character of the HBs, whereas OAH bonds have negative !2 q values. In addition, the weak intermolecular force due to dipole–dipole interaction (U) is also considered for analysis. The examination of HB in these complexes by quantum theory of NBO method fairly supports the ab initio results. Natural population analysis data, the electron density, and Laplacian properties, as well as, the m(OAH) and c(OAH) frequencies of complexes, calculated at the B3LYP/6-311þþG** level of theory, are used to evaluate the HB interactions. The calculated geometrical parameters and conformational analysis in water phase solution show that the H3COAHNCAR complexes in water are more stable than that in gas phase. The obtained results demonstrated a strong influence of the R substituent on the properties of complexes. Numerous correlations between topological, geometrical, thermodynamic properties, and energetic parameters were also found.