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- Sajan, D., et al.
(författare)
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Dimerisation and vibrational spectroscopic properties of (RS)-phenylsuccinic acid
- 2006
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 37:11, s. 1307-1318
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Tidskriftsartikel (refereegranskat)abstract
- Single crystals of (RS)-phenylsuccinic acid (RSPSA) were grown by the slow evaporation technique and vibrational spectral analysis was carried out using near-IR Fourier transform Raman and Fourier transform IR spectroscopy. The density functional theoretical (DFT) computations were also performed at the B3LYP/6-31G(d) level to derive the equilibrium geometry, vibrational wavenumbers, intensities and atomic charges. Vibrational spectral investigation confirmed the formation of cyclic dimers in the crystal, with the carboxyl groups of each acid molecule being hydrogen bonded to those of the adjacent molecules. Each molecule is connected to two other molecules, forming infinite chains. The wavenumber difference observed between the carbonyl modes in the IR and Raman spectra might be attributed to the intramolecular association based on C=O center dot center dot center dot H type hydrogen bonding in the molecule. In a hydrogen-bonded carbonyl, resonance can occur, which places a partial negative charge on the oxygen atom accepting the hydrogen bond and a positive charge on the atom donating the hydrogen. The resulting partial 'transfer of allegiance' of the proton enhances resonance and lowers the carbonyl stretching wavenumber. The O-H stretching vibrational wavenumber is red-shifted owing to the formation of strong O-H center dot center dot center dot O hydrogen bonds by hyperconjugation between carbonyl oxygen lone electron pairs and O-H sigma* antibonding orbitals. Vibrational analysis was used to investigate the C-H center dot center dot center dot O interaction and electronic effects, induction of the methylene group by an adjacent electronegative atom and the resulting increase of stretching mode wavenumbers and decrease of infrared intensities.
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| 2. |
- Sajan, D., et al.
(författare)
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Surface-enhanced Raman scattering and the adsorption behavior of (RS)-phenylsuccinic acid
- 2006
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 64:3, s. 580-585
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Tidskriftsartikel (refereegranskat)abstract
- The surface geometry of (RS)-phenylsuccinic acid molecule was studied by analysis of the SERS spectra of aromatic dicarboxylic acid adsorbed on silver colloid surfaces. For a reliable analysis of the SERS spectrum, we also performed density functional theoretical calculations. The SERS spectral features indicated that the RSPSA molecules should bound to the silver as dicarboxylate, with a strongly tilted orientation with respect to the normal to the surface. Such a tilted orientation was presumed to occur by the simultaneous sigma and pi-type coordination of carboxylate groups to silver surface caused by the steric hindrance and electrostatic repulsion between the two carboxylate groups, and thereby RSPSA on silver was easily displaced with aromatic carboxylic acids. A sigma-type coordination therefore seemed to be more important than a pi-type coordination for aromatic carboxylic acid derivatives to assemble on a silver surface. The large enhancement of in-plane bending, out of plane bending and ring breathing modes in the surface-enhanced Raman scattering spectrum indicates that the molecule is adsorbed on the silver surface in a 'atleast vertical' configuration, with the ring perpendicular to the silver surface.
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