Comparative structural and vibrational investigations in two different forms of the L-Tyrosine (L-TYR) have been carried out using Raman and IR spectral and DFT methods. For the optimized structures of the most stable conformers the vibrational assignments of the experimental IR and Raman bands have been proposed using the results of the DFT-B3LYP computations and the PEDs computed using GAR2PED software. The optimized geometrical structures of the molecule belong to the C1 point group in the zwitterionic and isolated forms of the molecule. Possibility of the charge transfer phenomena in the molecule has been investigated in light of the HOMO-LUMO analysis. The electron density mappings of the iso-surfaces with the molecular electrostatic potential (MEP) have been carried out to obtain the different information associated with the size, shape, charge density distribution and site of chemical reactivity of the molecule. On the basis of the NBO analysis presence of intramolecular H bonding and intramolecular charge transfer (ICT) have been proposed.

DFT calculations were carried out to compute the optimized molecular geometries, APT charges and fundamental vibrational frequencies along with their corresponding IR intensities, Raman activities and depolarization ratios of the Raman bands for the neutral Cyt and TCyt molecules and their cations and anions using the DFT/B3LYP method with the 6-311++G** basis set using the Gaussian-03 software. TCyt, Cyt + and TCyt + show planar structures and belong to C s point group symmetry while Cyt, Cytand TCytpossess non-planar structures with C 1 point group symmetry. Conformational analysis was carried out to obtain the most stable configurations of these molecules. The normal modes of vibration for all the species have been assigned on the basis of PEDs obtained from normal coordinate analysis using the GAR2PED software. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping the electron density isosurface with molecular electrostatic potential (MEP) surfaces. The energy gap from HOMO to LUMO of the Cyt is 5.2963 eV and that of TCyt is 5.0062 eV.

Vibrational characteristics of 2-nitrophenol have been investigated using experimental IR and Raman data and computational data using DFT method employing the 6-311++G** basis set available on Gaussian-09 software for the most stableconformer C-1. Complete vibrational assignments of the experimental IR and Raman bands have been proposed in light of the results obtained from the DFT computations and the PEDs computed using GAR2PED software. The optimized geometrical parameters suggest that the overall symmetry of the most stablemolecule is Cs. The molecule is expected to have three conformers. In the present article all the characterizations and the analyses of the lowest energy conformer of 2-NP have been studied. The charge transfer occurring in the molecule has been shown by HOMO-LUMO energy orbitals the energy gap of HOMO LUMO orbitals have been found 4.03eV. The mappings of electron density iso-surface with the electrostatic potential (ESP), has been carried out to get the information about the size, shape, charge density distribution and site of chemical reactivity of 2-NP. Current density and magnetic shielding of C-1 have been investigated. Some essential thermo molecular characteristics, namely, enthalpy, Gibb's free energy, thermal energy, entropy, heat capacity, internal energy and the partition functions of the molecule have also been analyzed.