FTIR spectroscopic evidence for new isomers of 3-aminopyrazine-2-carboxylic acid formed in argon matrices upon UV irradiations

Spectrochim Acta A Mol Biomol Spectrosc. 2021 Dec 15:263:120158. doi: 10.1016/j.saa.2021.120158. Epub 2021 Jul 8.

Abstract

The UV-induced photochemistry and molecular structure of 3-aminopyrazine-2-carboxylic acid were studied in argon matrices by Fourier-transform infrared spectroscopy and B3LYP/6-311++G(2d,2p) calculations. Out of seventeen possible isomers of this molecule located on the singlet potential energy surface the most stable one, APA1 comprising intramolecular O-H···N and N-H···O hydrogen bonds, was detected experimentally in the matrix after deposition. Two new conformers APA2 and APA3 were generated upon irradiation with λ = 280 nm by trans/cis-COOH isomerization and at λ = 360 nm by COOH group rotamerization, respectively, whereas an amino-imino tautomerization leading to IPA1 and IPA2 structures occurred at λ = 305 nm. The reverse reactions were also observed upon irradiation of the matrices at 265, 230 and 400 nm. Simultaneously with the photoisomerizations, a cleavage of the pyrazine ring along with CO2 elimination was observed leading to the formation of carbodiimide and cyanamide derivatives.

Keywords: Amino-imino tautomerization; Infrared spectra; Isomerization; Photochemistry; Rotamerization; UV laser-induced phototransformations.

MeSH terms

  • Argon
  • Isomerism
  • Pyrazines*
  • Spectroscopy, Fourier Transform Infrared

Substances

  • Pyrazines
  • 3-aminopyrazine-2-carboxylic acid
  • Argon