Theoretical study on the intramolecular hydrogen bond in chloro-substituted N,N-dimethylaminomethylphenols. I. Structural effects

Ab initio and density functional calculations are applied to study the influence of an increasing number of chlorine substituents on the properties of the intramolecular hydrogen bond in substituted Mannich bases. It is shown, that not only the acidity of the proton donor, which depends on the number of chlorine atoms at the aromatic ring, but also steric interactions modify the geometry of the hydrogen bond. Specific interactions of O–ClH–O hydrogen-bonding in some derivatives are estimated by calculations on related chlorophenols.     

Structure of the complex of dimethylphenyl betaine with dichloroacetic acid studied by X-ray diffraction,DFT calculations,infrared and Raman spectra

The structure of the complex of dimethylphenyl betaine (DMPB) with dichloroacetic acid (DCA) (1) has been investigated by X-ray diffraction, FTIR and Raman spectroscopy, and B3LYP/6-311 + + G(d,p) calculations. The crystal is monoclinic, space group P2₁. The acid is connected with betaine through the OH⋯O hydrogen bond of 2.480(2) Å. In the optimized structure the short, asymmetric O⋯O distance is 2.491 Å. FTIR spectrum shows a broad absorption in the 1500–400 cm⁻¹ region characteristic of very short OH⋯O hydrogen bond caused by Fermi resonance between νOH and overtones of δOH and γOH. In the Raman spectrum this broad absorption is not observed. The potential energy distributions (PED) were used for the assignments of IR and Raman frequencies in the experimental and calculated spectra. The FTIR and Raman spectra of the crystal complex are consistent with the X-ray results.     

Intramolecular hydrogen bonds in the sulfonamide derivatives of oxamide, dithiooxamide, and biuret. FT-IR and DFT study, AIM and NBO analysis

The hydrogen bonding in [(1-arylsulfonylamino-2,2,2-trichloro)ethyl]biuret 1, [(1-arylsulfonylamino-2,2,2-trichloro)ethyl]oxamide 2, and [(1-arylsulfonylamino-2,2,2-trichloro)ethyl]dithiooxamide 3, the sulfonamide derivatives of biuret 4, oxamide 5, and dithiooxamide 6, has been studied by molecular spectroscopy and DFT theoretical calculations including frequency calculations, at the B3LYP/6-311+G(d,p) level of theory. The analysis of the CO?HN and CS?HN intramolecular hydrogen bonds closing the five- and six-membered rings employing the atoms-in-molecules (AIM) method using the MP2(full)/6-311++G(d,p) wave functions has shown that their stability is increased in comparison to the original molecules and is much higher in the thiocarbonyl compounds. The results of the AIM and the NBO analysis of donor-acceptor interactions are in good agreement with each other and with the experimental FT-IR spectroscopy data.