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Radical Anions of Cyclic Azoalkanes: An ESR, ENDOR, and TRIPLE‐Resonance Study
Author(s) -
Ess Caspar H.,
Gerson Fabian,
Adam Waldemar
Publication year - 1992
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19920750130
Subject(s) - chemistry , hyperfine structure , hyperfine coupling , coupling constant , resonance (particle physics) , counterion , crystallography , anisotropy , radical , stereochemistry , ion , atomic physics , organic chemistry , quantum mechanics , physics , particle physics
Radical anions of ten monocyclic and bicyclic azoalkanes containing the azo group in (Z)‐conformation, have been fully characterized by their hyperfine data with the use of ESR, ENDOR, and general‐TRIPLE‐resonance spectroscopy. These azoalkanes are represented by 3,3,5,5‐tetramethyl‐1‐pyrazline ( 1 ), 2,3‐diazabicyclo[2.2.1]hept‐2‐ene ( 4 ), and 2,3‐diazabicyclo[2.2.2]oct‐2‐ene ( 9 ), as well as by their derivatives 2, 3, 5–8 , and 10. For all radical anions \documentclass{article}\pagestyle{empty}\begin{document}$1^{- \atop \dot{}}-10^{- \atop \dot{}}$\end{document} , the 14 N‐coupling constant, a N , is in the range of +0.83 to +0.97 mT; this finding indicates that the spin population is essentially restricted to the π system of the azo group. The 14 N‐hyperfine anisotropy largely affects the width of ESR lines, particularly at low temperatures. Substantial coupling constants of 7 Li‐, 23 K‐, and 133 Cs‐nuclei point to a close association of the radical anions with their alkakimetal counterions. With the exception of 39 K, these nuclei give rise to readily observable ENDOR signals which appear along with those stemming from protons. The prominent hyperfine features of \documentclass{article}\pagestyle{empty}\begin{document}$1^{- \atop \dot{}}-10^{- \atop \dot{}}$\end{document} are discussed.