Ab initio MO and density functional studies on the vibrational spectra of 1,4-benzoquinone, and its anion and dianion

p-Benzosemiquinone radical anion on silver nanoparticles in water

This communication reports the SERS observation of p-benzosemiquinone radical anion, produced on reduction of p-benzoquinone by Ag nanoparticles at the metal-water interface. The species is positively identified by comparison of the SERS spectrum with the resonance Raman spectra of the radical anion in aqueous solution. This is a rare SERS observation of a radical intermediate formed by surface reaction on nanosize silver particles in solution.

The anomalous solvent effect in the vibrational spectrum of 2,3-diphenyl-cycloprop-2-enone: an experimental and theoretical investigation

2,3-Diphenyl-cycloprop-2-enone (DPC) was investigated aiming to understand the origins of the anomalous solvatochromism in its vibrational spectrum. Its Raman and IR spectra in several solvents were obtained revealing that the v(C=C) mode is much more sensitive to the solvent than the v(C=O) mode. Hartree-Fock and density functional theory calculations were undertaken for obtaining the structure and the vibrational spectra of DPC and 2,3-dimethylcycloprop-2-enone (DMC), revealing that both in terms of structure as well as of vibrational spectrum, DPC and DMC are very similar. Such results indicated that DMC could be used as a model system to simulate the solvent effect in DPC, what was done using three different methods: the first takes into account the dielectric effect via the self-consistent reaction field (SCRF); the second is the supermolecular approach that considers explicity the formation of solute-solvent clusters and the third is a combined approach, SCRF + supermolecule. The anomalous solvatochromism in the vibrational spectrum of DPC can be understood on basis of the significant participation of the v(C=O) mode in the one assigned to the v(C=C) vibration, as well as by the presence of a Fermi resonance involving the former. In addition, the v(C=O) mode involves a significant participation of the (C-C) mode (C(cyclopropene)-C(phenyl)) and the two interatomic distances, C=O and C-C, show opposite trends with increasing solvent polarity. Summing up, the anomalous solvatochromic effect of DPC can be understood by the complex composition of its v(C=O) mode that, in addition, is affected by the presence of a Fermi resonance.