C. Ravikumar

Spectroscopic analysis and DFT calculations of a food additive carmoisine.

FT-IR and Raman techniques were employed for the vibrational characterization of the food additive Carmoisine (E122). The equilibrium geometry, various bonding features, and harmonic vibrational wavenumbers have been investigated with the help of density functional theory (DFT) calculations. A good correlation was found between the computed and experimental wavenumbers. Azo stretching wavenumbers have been lowered due to conjugation and pi-electron delocalization. Predicted electronic absorption spectra from TD-DFT calculation have been analysed comparing with the UV-vis spectrum. The first hyperpolarizability of the molecule is calculated. Intramolecular charge transfer (ICT) responsible for the optical nonlinearity of the dye molecule has been discussed theoretically and experimentally. Stability of the molecule arising from hyperconjugative interactions, charge delocalization and C-H ...O, improper, blue shifted hydrogen bonds have been analysed using natural bond orbital (NBO) analysis.

Electronic absorption and vibrational spectra and nonlinear optical properties of 4-methoxy-2-nitroaniline

FT-Raman, IR and UV-vis spectroscopies have been applied to investigate the potential nonlinear optical (NLO) material 4-methoxy-2-nitroaniline. A detailed interpretation of the vibrational spectra was carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology. Density functional theory is applied to explore the nonlinear optical properties of the molecule. The study suggests the importance of pi-conjugated systems for nonlinear optical properties and the possibility of charge transfer interactions. Good consistency is found between the calculated results and experimental data for the electronic absorption, IR and Raman spectra. The solvent effects have been calculated using time-dependent density functional theory in combination with the polarized continuum model, and the results are in good agreement with experimental measurements. The calculations reveal that incorporation of substituents (amino, nitro and methoxy) has a strong influence on the structure and spectroscopic properties of the molecule, and the effect of electron charge transfer was examined by natural bond orbital population analysis.

NBO analysis and vibrational spectra of 2,6-bis(p-methyl benzylidene cyclohexanone) using density functional theory

Vibrational analysis of the 2,6-bis(p-methyl benzylidene cyclohexanone) [PMBC] compound was carried out by using NIR FT-Raman and FT-IR spectroscopic techniques. The equilibrium geometry, various bonding features and harmonic vibrational frequencies of PMBC have been investigated with the help of B3LYP/6-31 G(d) density functional theory method. The optimized geometry clearly demonstrates cyclohexanone ring chair conformation is changed into half-chair conformation. The shortening of C-H bond length and blue shifting of the CH stretching wavenumber suggest the existence of improper weak C-H***O hydrogen bonding, which is confirmed by the natural bond orbital analysis. The Mulliken population analysis on atomic charges and the HOMO-LUMO energy are also calculated.

Vibrational spectra and normal coordinate analysis of plant growth regulator 1-naphthalene acetamide

FT Raman and IR spectra of the biologically active molecule, 1-naphthalene acetamide (NA) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers of NA have been calculated with the help of B3LYP density functional theory (DFT) method. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The downshifting of NH(2) stretching wavenumber indicates the formation of intermolecular N-Hcdots, three dots, centeredO hydrogen bonding. The NBO analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule.

Analysis of vibrational spectra of L-alanylglycine based on density functional theory calculations

FT Raman and IR spectra of the crystallized biologically active molecule, L-alanylglycine (L-Ala-Gly) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational frequencies of L-Ala-Gly have been investigated with the help of B3LYP density functional theory (DFT) method. The calculated molecular geometry has been compared with the experimental data. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The optimized geometry shows the non-planarity of the peptide group of the molecule. Potential energy surface (PES) scan studies has also been carried out by ab initio calculations with B3LYP/6-311+G** basis set. The red shifting of NH3+ stretching wavenumber indicates the formation of N-H...O hydrogen bonding. The change in electron density (ED) in the sigma* antibonding orbitals and E2 energies have been calculated by natural bond orbital analysis (NBO) using DFT method. The NBO analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule.

Growth and Vibrational Spectroscopic Investigations of NLO Crystal Barium Thiourea Chloride

The crystal of NLO interest, Barium thiourea chloride (BTC) has been crystallized and is subjected to FT‐IR and NIR FT‐Raman spectral studies along with the quantum chemical computations. The equilibrium geometry, first hyperpolarizability, various bonding features and vibrational wavenumbers have been calculated by B3LYP density functional theory (DFT) calculations at the LANL2DZ level. The predicted vibrational spectra are in fair agreement with the experiment. The broadening of NH2 stretching wavenumber indicates the intermolecular N‐H…CI hydrogen bonding present in the molecule.

Synthesis and Spectroscopic Investigations of NLO Crystal L‐Valine Formate

Vibrational spectral analysis of the nonlinear optical (NLO) crystal, L‐Valine formate (LVF) was carried out using NIR FT‐Raman spectroscopy. The equilibrium geometry, bonding features harmonic vibrational frequencies and first hyperpolarizability of LVF have been investigated with the help of B3LYP density functional theory (DFT) method. The NLO efficiency, predicted in this material, has been confirmed by Kurtz‐Perry powder SHG experiments. The red shifting of NH3+ stretching wavenumber indicates the formation of N–H⋯O hydrogen bonding.

Potential Energy Surface Scan Studies and NBO Analysis of L‐Alanylglycine Crystal: A Vibrational Approach

Vibrational spectral analysis of L‐Alanylglycine (L‐Ala‐Gly) is carried out using NIR FT‐Raman and FT‐IR spectroscopy, supported by density functional theory (DFT) calculations to obtain the equilibrium geometry, bonding features and harmonic vibrational frequencies. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). Potential energy surface (PES) scan studies has also been carried out by ab initio calculations with B3LYP/6‐311+G** basis set. The natural bond orbital (NBO) analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule.Vibrational spectral analysis of L‐Alanylglycine (L‐Ala‐Gly) is carried out using NIR FT‐Raman and FT‐IR spectroscopy, supported by density functional theory (DFT) calculations to obtain the equilibrium geometry, bonding features and harmonic vibrational frequencies. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). Potential energy surface (PES) scan studies has also been carried out by ab initio calculations with B3LYP/6‐311+G** basis set. The natural bond orbital (NBO) analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule.

Vibrational Spectral Simulation of 1‐Benzyl‐1H‐Imidazole Using Scaled DFT Force Fields

The Fourier Transform Raman and infrared spectra of the crystallized pharmaceutical molecule 1‐benzyl‐1H‐imidazole (BI) have been recorded and analyzed. The geometry, intermolecular hydrogen bond, and harmonic vibrational frequencies of BI have been predicted with the help of B3PW91 density functional theory (DFT) methods. The vibrational spectra have been simulated with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The pronounced double‐bond derealization in the imidazole ring upon intermolecular H‐bonding becomes the cause for its enhanced aromaticity.

Spectroscopic Investigations and Quantum Chemical Computations of NLO Material Bis (4‐Nitrophenyl) Carbonate

NIR FT‐Raman and FT‐IR spectra of the non linear optic (NLO) material, Bis (4‐Nitrophenyl) carbonate (BNPC) have been recorded and analyzed. Ab initio quantum chemical computations have been performed at HF/6‐31G(d) level to compute the optimized geometry, vibrational wavenumbers, intensities and first hyperpolarizability. The SHG property is studied by Kurtz‐Perry powder technique. The splitting of the C=O stretching frequency caused by expanded conjugation effects in the carbonate group. The optimized geometry explains that the molecule BNPC is s‐cis‐s‐cis conformation of the carbonate group.