Masumi Yamakawa

Absorption and phosphorescence spectra of 4-nitropyridine N-oxides and 4- and 3-nitroquinoline N-oxides

Abstract The absorption, phosphorescence and phosphorescence excitation spectra of 4-nitropyridine N-oxide (4NPO) and its methyl derivatives, 4-nitroquinoline N-oxide (4NQO), and 3-nitroquinoline N-oxide (3NQO) were recorded. For 4NPO, the lifetime of phosphorescence, degree of polarization of the phosphorescence and excitation spectra, and the singlet—triplet separation energy were analyzed in detail. The experimental results were also compared with those of SCFMOCI calculation. The following results are reported. (i) The electronic spectra of 4NPO, 4NQO and 3NQO, and the effect of steric hindrance on the spectra are interpreted by the aid of theoretical calculation. At the longest wavelength absorption band the intramolecular charge transfer from the N-oxide group oxygen atom to the nitro group is the main configuration, which may play an important role in the photochemical reaction of these substances. (ii) A blue shift was always observed in the phosphorescence spectra on changing the solvent from ether to isopropyl alcohol, the importance of hydrogen bonding effect on this phenomenon being stressed. (iii) The characteristics of the lowest triplet state of the N-oxides are discussed in detail on the basis of the spectroscopic information. It is concluded that the lowest triplet state is of the nature of a π—π* transition, for 4NPO this being 3 A 1 .

A theoretical study of the substituent effect on the infrared intensities of the CN stretching mode of benzonitrile derivatives

Abstract The substituent effect on the integrated intensities of the characteristic CN infrared band of benzonitrile derivatives was studied using the CNDO 2 method. The charge flux term plays an important role in the substituent effect on the intensities and the fixed charge term does not have a predominant effect on the intensities. The contributions of the π, π, and σ electron systems to the charge flux term are discussed in detail.

Ultraviolet absorption spectra of trimethylamine N-oxide

Abstract Ultraviolet absorption spectra of trimethylamine N-oxide were recorded in several solvents, a band being found around 198 mμ with ϵ ≈ 2350 in acetonitrile solvent. However, in ethyl alcohol and in water this band undergoes a large blue shift and decreases in intensity. These phenomena were mainly ascribed to the hydrogen bonding interaction of the amine oxide with the solvents. Experiments with the three-component system (solvent, CH3CN and proton donor, CH3OH) showed that no charge-transfer band pertaining to hydrogen bonding, (CH3)3NO⋯HOCH3, appears in the wavelength region longer than 200 mμ. The observed band is now assigned as an n → σ ∗ transition on the basis of the facts: (i) the blue shift phenomenon in solvents like alcohol as mentioned above, and (ii) a theoretical intensity calculation under the assumption that the above 198-mμ band is due to the n → σ ∗ transition arising from an electron transition of a lone pair electron of the oxygen atom to the antibonding σ molecular orbital of the NO bond gives semiquantitative agreement with the experimental value.

A relationship between infrared band intensity and configuration of the cyano group in simple and fused cyclohexanecarbonitriles

Infrared spectral measurements were carried out to obtain the integrated intensity of the stretching vibration band of the cyano group in simple and fused cyclohexanecarbonitriles in carbon tetrachloride solution. A linear relationship was found between the integrated intensity and the square of the number (N) of Cβ–Cγ bonds parallel to the CN bond. This result was theoretically supported by CNDO/2 calculations.