Open AccessExperimental and theoretical investigation of C-nitroso rotation in 2-nitrosoimidazoles
Author(s) -
Judy L. Bolton,
Michael R. Peterson,
Robert A. McClelland
Publication year - 1988
Publication title -
canadian journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.323
H-Index - 68
eISSN - 1480-3291
pISSN - 0008-4042
DOI - 10.1139/v88-471
Subject(s) - chemistry , nitroso , nitroso compounds , dimer , imidazole , ab initio , monomer , crystallography , computational chemistry , nuclear magnetic resonance , stereochemistry , medicinal chemistry , organic chemistry , physics , polymer
1-Methyl-2-nitrosoimidazole exhibits broadened 1 H nuclear magnetic resonance signals at room temperature. The concentration independency of this spectrum as well as the linearity of the 700-nm absorbance with concentration rules out equilibrating nitroso monomer – nitroso dimer. It is suggested that there are equilibrating s-cis and s-trans nitroso monomer rotational isomers. At −59 °C two sets of signals in a 3:1 ratio are observed. Analysis of CH 3 chemical shifts in terms of the magnetic anisotropy of the nitroso group suggests that the s-trans is the major isomer. The broadening observed at higher temperatures leads to a barrier for rotation (from the trans isomer) of 12.4 kcal mol −1 . Ab initio calculations with 2-nitrosoimidazole using the 3-21G basis set show that the fully planar s-cis and s-trans forms are minima, with the s-trans more stable by 2.5 kcal mol −1 , and a barrier to rotation (from the s-trans) of 13.0 kcal mol −1 . These results are in good agreement with those from solution phase. Various factors suggest that the π conjugative interaction between the nitroso group and imidazole ring is relatively unimportant.