Solvent Shift Method Research Articles

Excited-state dipole moment changes in some pseudoazulenes

The solvent-shift method was used to determine dipole moment changes on electronic excitation in pseudoazulenes, derivatives of 7-azaindole. The dipole moment is reduced, and in S 1 its direction is opposite to that of the ground state. The appropriate value of the Onsager radius corresponds to the chromophore part only: the chromophore and the substituent process their own Onsager cavities.

Excited state properties of nitrobenzene derivatives

Gas-phase and solution spectra of methoxy nitroanilines are reported. MIM and PPP configuration analyses were used to calculate the properties associated with the electronic transitions. The excited state dipole moments associated with the first intense electronic transition were evaluated by the solvent shift method. The spectra of the title compounds are tentatively correlated with those of the corresponding disubstituted benzene derivatives. The effect of the methoxy group on the absorption features of the isomeric nitroanilines is briefly discussed.

The i.r. spectroscopy of some highly conjugated systems—I. Rationale of the investigation

The solvent shift method of BELLAMY is re-examined, particularly as a tool for the identification of vibrations that include and are coupled to carbonyl, all of which show solvent sensitivity. For α,β-unsaturated ketones, it is shown that s-cis and s-trans conformers are readily distinguished by plots of νCC vs. νCO. The nature of this coupling is discussed and it is concluded that, in so far as coupling occurs, νCO and νCC take on the character of out-of-phase and in-phase modes respectively. In either conformer, the in-phase (νCC) mode gains in relative intensity as the frequencies converge. While s-cis conformers couple more, conjugation is unaffected by this; the true index of conjugation is neither νCO nor νCC but mean frequency ν m . The whole of the solvent effect appears to be relayed by carbonyl: even a highly polar carbon double bond is insensitive to solvent unless so coupled.

Solvent effects in nuclear magnetic resonance spectroscopy. Part XIII. Solvent shifts induced by benzene in some α,β-unsaturated compounds. An aid to the determination of stereochemistry

The solvent shifts (Δ=δCCl4–δC6H6 or δCCl4–δC6D6 p.p.m.) of proton resonances in some α,β-unsaturated acids, esters, nitriles, halides, and nitro-compounds have been determined. In general preferential shielding in benzene solution of the protons trans to the polar substituent is observed. The solvent shifts are therefore of assistance in the determination of stereochemistry in such compounds. The solvent shift method is used to confirm previous stereochemical assignments in geranic and phytenoic acids.