Scaled Quantum Mechanical Methodology Research Articles

Synthesis and characterization of cinnamylidene acetone – A study on tuning of band gap by vibrational spectroscopic tools

The title molecule Cinnamylidene acetone (CA) was synthesized through a single step base catalyzed aldol type condensation between acetone and cinnamaldehyde. The prepared molecule has been characterized using NMR (1H and 13C) spectral analysis, FTIR, UV–Vis and Elemental analysis. The complete vibrational characterization of the molecule was performed using experimental (FTIR and FT-Raman) spectra and calculations at DFT level. In order to carry out a detailed vibrational spectroscopic analysis of CA, Fourier Transform Infrared and Fourier Transform Raman spectra recorded in condensed phase were used. To determine the optimized geometry and vibrational wavenumbers, Density functional theory calculations in the B3LYP/6-31G** level have been carried out followed by scaling using the scaled quantum mechanical methodology. A root mean square deviation of 6.53 cm−1 has resulted from the scaled quantum mechanical treatment. The ultraviolet visible spectra of the title compound dissolved in various solvents were recorded in the range of 300–600 nm. The natural bond orbital and frontier molecular orbital analyses were also performed using B3LYP/6-31G** method. These studies revealed a reduction in the band gap of CA in comparison with that of cinnamaldehyde (CY).

Structural and spectroscopic study of a pectin isolated from citrus peel by using FTIR and FT-Raman spectra and DFT calculations

In this work, pectin isolated from citrus peel with a degree of esterification of 76% was characterized by Fourier Transform Infrared (FTIR) and Fourier Transform Raman (FT-Raman) spectroscopies. Structural studies were carried out taking into account their partial degree of esterification and considering the polygalacturonic acid chain as formed by two different subunits, one with both COOH and COOCH3 groups (Ac) and the other one as constituted by two subunits with two COOCH3 groups (Es). Their structural properties, harmonic frequencies, force fields and force constants in gas and aqueous solution phases were calculated by using the hybrid B3LYP/6-31G∗ method. Then, their complete vibrational analyses were performed by using the IR and Raman spectra accomplished with the scaled quantum mechanical (SQM) methodology. Reactivities and behaviors in both media were predicted for Ac and Es by using natural bond orbital (NBO), atoms in molecules (AIM), and frontier orbitals calculations. We report for first time the complete assignments of those two different units of polygalacturonic acid chain which are the 132 normal vibration modes of Ac and the 141 normal vibration modes of Es, combining the normal internal coordinates with the SQM methodology. In addition, three subunits were also studied. Reasonable correlations between the experimental and theoretical spectra were obtained. Thus, this work would allow the quick identification of pectin by using infrared and Raman spectroscopies and also provides new insight into the interactions that exist between subunits of a large pectin chain.

An insight into the conformal flexibility and vibrational behavior of 2-nitroso-1-naphthol: A density functional theory approach

ABSTRACTThe conformational stability of 2-nitrosol-1-naphthol (2N1N) was elucidated using potential energy surface scan studies. In order to carry out a detailed vibrational spectroscopic analysis of 2N1N, Fourier transform infrared and Fourier transform Raman spectra have been recorded in condensed phase. To determine the optimized geometry and vibrational wavenumber, density functional theory calculations in the B3LYP/6-31G** level have been carried out followed by scaling using the scaled quantum mechanical methodology. A root mean square deviation of 9.69 cm−1 has resulted from the scaled quantum mechanical treatment. Substitution of nitroso group into the 1-naphthol has produced remarkable changes in the structural parameters. The ultraviolet-visible spectra of the title compound dissolved in various solvents were recorded in the range of 300–500 nm. The natural bond orbital analysis, frontier molecular orbital analysis, and thermodynamic features were also performed using B3LYP/6-31G** method.