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Abstract: Vibrational analysis of the thionocarbamate fungicide tolnaftate which is antidermatophytic, antitrichophytic and antimycotic agent, primarily inhibits the ergosterol biosynthesis in the fungus, was carried out using NIR FT-Raman and FTIR spectroscopic techniques. The equilibrium geometry, various bonding features, harmonic vibrational wavenumbers and torsional potential energy surface (PES) scan studies have been computed using density functional theory method. The detailed interpretation of the vibrational spectra has been carried out with the aid of VEDA.4 program. Vibrational spectra, natural bonding orbital (NBO) analysis and optimized molecular structure show the clear evidence for electronic interaction of thionocarbamate group with aromatic ring. Predicted electronic absorption spectrum from TD-DFT calculation has been compared with the UV–vis spectrum. The Mulliken population analysis on atomic charges and the HOMO–LUMO energy were also calculated. Vibrational analysis reveals that the simultaneous IR and Raman activation of the C–C stretching mode in the phenyl and naphthalene ring provide evidence for the charge transfer interaction between the donor and acceptor groups and is responsible for its bioactivity as a fungicide. [Copyright &y& Elsevier]

Abstract: NIR FT-Raman and IR spectra of the biologically active molecule, chlorothalonil have been recorded and analyzed. The molecular geometry and vibrational wavenumbers of the title compound in the ground state have been calculated by density functional theory (DFT) with 6-31G(d) basis set. In order to obtain the information about the influence of intramolecular interaction on the molecule, the calculated geometries of chlorothalonil molecule was compared with the experimental data. The results of the optimized molecular structure gave clear evidence for the intramolecular charge transfer (ICT). Time-dependent density functional theory (TD-DFT) calculation of the electronic spectra has been performed and compared with the experimental UV–visible spectrum. Mulliken''s net charges have been calculated and compared with the atomic natural charges. The effects of chlorine and cyanide group substituent in benzene ring in the vibrational wavenumbers have been analyzed. NBO analysis is useful to understand the intramolecular hyperconjugative interaction between lone pair Cl and σ*(C–C) bond orbital. [Copyright &y& Elsevier]