Vibrational Spectra,Assignments,and Valence Force Field for S-nitrosocysteine and Isotopic Analogs

Abstract

S-nitrosocysteine and the isotopically-substituted S¹⁵NO and N-d₃ analogs have been prepared. FT-IR spectra have been obtained on the normal molecule and the ¹⁵N isotopomer. Spectra of the N-d₃ analog were obtained with a dispersive instrument. The fundamental frequencies of the three isotopomers were calculated by using force constants previously obtained through overlay calculations on amino acids and from a normal coordinate analysis of methyl thionitrite. The average computational error between the observed and calculated frequencies using the transferred force constants was 11 cm⁻¹. This difference was decreased to 7 cm⁻¹ by slightly modifying some of the force constant values by a least-squares refinement. Vibrational assignments are made for all three isotopic analogs by utilizing the potential energy distribution. Out of a total of 96 fundamentals occurring above 300 cm⁻¹, 65 may be classified as group vibrations by the potential energy criterion.