Elucidation of structure − property correlations using experimental Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FTIR) specroscopy analysis, and Density Functional Theory (DFT) calculations of the Difurylmethane (DFM) molecule, and difurylmethane-methanol clusters

Abstract

Ab Initio Hatree-Fock (HF) and Density Functional Theory (DFT) are used to study the molecular structure of difurylmethane (DFM) and its interaction with methanol (MeOH) in the formation of DFM-MeOH complexes. The molecular structure of difurylmethane is further probed by using experimental proton nuclear magnetic resonance (1H-NMR), Gauge Including Atomic Orbital Nuclear Magnetic Resonance (GIAO-NMR), Fourier Transform Infrared (FTIR) spectroscopy analysis to elucidate any structure-property relations which may play a role in the DFM-MeOH complex formation. Conclusions from previous work in the researcher’s laboratory on ultrasonic speeds and volumetric studies of mixtures of DFM and a series of (C1-C6)-n-alkanol binary solutions underpins dipole-dipole interactions and possibly hydrogen bonding as the main intermolecular forces between molecules in the solution. To probe this further a theoretical and experimental investigations on the system is required. The scope of this work is to study the interactive behavior of DFM-MeOH complex system through computational methods using relevant model chemistries. The geometries of DFM molecular structures were optimized without symmetry constraints, using Gaussian ’09 package with B3LYP / 6-31+G (3d, 3p) method. The nature of stationary point was evaluated using harmonic frequency analysis and it was confirmed to be a local minimum in the potential energy surface. The potential energy surface scanning tool (PESST) was used to generate 12 conformational structures of DFM, by varying the angle between two furanic rings at an increment of 30 degrees. The global minimum in the Potential Energy Surface is located when the oxygen atoms in the furan rings are as far away from each other as possible and on opposite sides. Results from experimental 1H-NMR and FTIR spectroscopy analysis of the DFM molecule agree with the molecular structure obtained from computational B3LYP/6-31+G(3d,3p) methodology For the DFM-Methanol complexes, two equilibrium complexes were obtained and identified as either σ-type or π-type configurations where the –OH moiety of the methanol with the oxygen atom of the furan ring in the σ-type and the –OH interacts with the π-system of the furanic ring in the π-type configuration respectively. The basis set superposition error (BSSE) and thermal energy (calculated under the harmonic-rigid rotor approximation) corrected stabilization energies associated with the σ-type and π–type configurations are -3.16 kcal / mol. and -1.89 kcal / mol. suggesting that the σ-type configuration is the most favorable interaction. In a different study Kgagodi and Mbaiwa did similar study on DFM-n-propanol binary mixture (employing Molecular Mechanics and ab-initio methods) looking at the thermodynamic properties and structure. The results obtained from radial distribution functions and ab-initio calculations show evidence of hydrogen bonding between n-propanol and DFM via the acidic hydrogen of -OH group in MeOH and the hetero atom of DFM which is agreement with conclusions from this study on the most probable interaction between DFM and R-OH.