engleski

ANALYSIS OF CONFORMATIONAL SPACE AND COMPARISON OF CALCULATED VIBRATIONAL SPECTRA FOR A STRUCTURALLY RELATED MOLECULES

Vibrational spectra have been calculated with B3LYP method using the 6-31G* basis set for a number of structurally related benzene derivative and a comparison was made. These molecules are benzaldehyde (BA), trans-azobenzene (tAB), salicylideneaniline (SAN), trans-stilbene (tSB), 1,4-distyrylbenzene (DSB) and p,p'-distyrylstilbene (DSS). We have examined changes in vibrational dynamics with the respect to the number of rings in the chain (tSB-DSB-DSS) and number of different conformers. We have also examined changes with the respect to different kinds of atom in the bridging group (tSB-tBA-SAN). Results were compared with calculated potential energy distribution for normal modes of BA. Calculated spectra shows a very good agreemant with our own experimental spectra. Analysis of potential energy distribution for individual normal modes of different conformers (DSB, DSS) has shown that different conformations have similar frequency values but vibrational dynamics is different. The assumption of the presence of different stable conformers was confirmed. We have calculated bariers of rotation for different kinds of low-frequency motions in some molecules. The potential curve for a rotation of salycilidene ring in SAN predicts an existence of four stable conformers, i. e. two pairs of enantiomers. Potential energy curve will be presented and disscused

DFT; vibrational spectra

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