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  Physics Express 2014, 4: 12
  Research Article
Molecular structure, FT-IR, FT-Raman, NMR studies and first order molecular hyperpolarizabilities of 7-methoxy-4-methylcoumarin by DFT Method
  N. Prabavathi, N. Senthil Nayaki  
Department of Physics, Sri Sarada College for Women (Autonomous), Salem – 636 016, India
  The present study aims at elucidating the structural information and vibrational frequencies of 7-methoxy-4-methylcoumarin (7MMC) based on density functional theory (DFT) calculations. A complete vibrational analysis has been attempted on the basis of experimental infrared and Raman spectra of the titled molecule. Vibrational spectra of the selected molecule is simulated and compared with the experimental spectra. The equilibrium geometry, vibrational frequencies, band intensities, NMR spectra, NBO analysis and UV–Vis spectral studies of the most stable geometry have been calculated by density functional B3LYP method with the 6-311G++ (d, p) basis set. The theoretical UV–visible spectrum of the compound have been simulated using single-excitation configuration interactions (CIS) method and the electronic properties such as HOMO and LUMO energies are performed by time-dependent DFT (TD-DFT) approach. The first order hyperpolarizability (α0) of this novel molecular system and related properties (β, α0 and Δα) of 7MMC are calculated using DFT/6-311++G (d, p) method on the finite-field approach. The NBO (Natural Bonding Orbital) analysis is proved to be an effective tool for interpretation of hyper conjugative interactions and electron density transfer from the filled lone pair electron. The change in electron density in the σ* antibonding orbitals and stabilization energies were calculated by NBO analysis to give clear evidence of stabilization, originating in the hyper conjugation of hydrogen–bonded interactions. The 1H and 13C NMR spectra of 7MMC have been recorded and compared with the theoretically calculated values using the gauge independent atomic orbital (GIAO) method and their respective linear correlations were analyzed. A great deal of information regarding shielding and deshielding of protons can be obtained using NMR spectroscopy.
  Vibrational spectra; NMR; DFT; Natural Bond Orbitals; HOMO- LUMO; 7-methoxy-4-methyl coumarin  

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