Near Ultraviolet Solution Spectra of the Diazines

Abstract

The near ultraviolet spectra of the diazines and various derivatives have been obtained in several solvents. Intensities, contours, and positions of the observed bands are combined with a valence-bond treatment of the diazine π-electrons to assign the transitions and to evaluate the C–C and C–N exchange integrals. The diazine band near 30,000 cm−1 (3333A) is assigned to a nonbonding nitrogen electron transition, and the band near 40,000 cm−1 (2500A) to a π-electron transition.

The Role of the nπ* 1Au State in the Photoabsorption and Relaxation of Pyrazine

“…In terms of symmetry, the ground state is designated as S 0 1 A g of the D 2h point group, and the lowest singlet np* and pp* excited states have conventionally been assigned as S 1 1 B 3u and S 2 1 B 2u , respectively. The details in the ultraviolet absorption spectra of pyrazine were first resolved in solution in 1950s, [1] and the data from vapors were obtained in the following decades. [2][3][4][5][6][7] People found that the 325 nm absorption band, that is, the np* 1 B 3u state, has a lot of sharp peaks that have been assigned as n 6a (a g ), n 9a (a g ), n 10a (b 1g ) fundamentals and their overtones as well as combination bands.…”

“…Domcke and co-workers firstly carried out ab initio calculations combined with mathematical models to describe this internal conver-Abstract: The geometric, energetic, and spectroscopic properties of the ground state and the lowest four singlet excited states of pyrazine have been studied by using DFT/TD-DFT, CASSCF, CASPT2, and related quantum chemical calculations. The second singlet np* state, 1 A u , which is conventionally regarded dark due to the dipole-forbidden 1 A u ! 1 A g transition, has been investigated in detail.…”

A study on the electronic spectra of vinylpyridines and 1,2‐(dipyridyl)ethylenes. Molecular orbital calculations

“…The features of the spectra of vinylpyridines are not similar to that of pyridine [14]; this dissimilarity indicates that the molecule is a rigid planar one and not a free rotator. Consequently, the extension of conjugation is pronounced and the ortho-ortho hydrogen steric effect is negligible.…”

Spectroscopic Studies of d‐Pilocarpine and Some Quaternary Derivatives

“…The spectra of five representative quaternary compounds (3, 6, II, 14 and 16) lack the distinct 215 nm band, which is replaced by a rather broad shoulder (e -3280) centered at the same place. The appearance of such a shoulder may be related to a certain shift due to the newly formed C -N bond, reflecting a reduced delocalization of the electron pair [7]. No change in the 250 nm band was detected.…”