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1,2‐Dihydrotriazinyl‐ N ‐oxy Free Radicals
Author(s) -
Brough Peter,
Gambarelli Serge,
Jacquot JeanFrançois,
Grand André,
Pécaut Jacques,
Rey Paul
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201100433
Subject(s) - delocalized electron , radical , chemistry , electron paramagnetic resonance , unpaired electron , hyperfine structure , crystallography , nitrogen , oxide , reagent , ring (chemistry) , medicinal chemistry , photochemistry , nuclear magnetic resonance , organic chemistry , physics , atomic physics
Triazinyl‐ N ‐oxy free radicals, 2‐methyl‐2,4,6‐triphenyl‐1,2‐dihydro‐1,3,5‐triazinyl‐1‐oxy ( 6 a ), 2,2,4,6‐tetraphenyl‐1,2‐dihydro‐1,3,5‐triazinyl‐1‐oxy ( 6 b ), 2,2‐dimethyl‐4,6‐diphenyl‐1,2‐dihydro‐1,3,5‐triazinyl‐1‐oxy ( 13 ), and 2,6‐dimethyl‐2,4‐diphenyl‐1,2‐dihydro‐1,3,5‐triazinyl‐1‐oxy ( 14 ), in which the unpaired electron is delocalized over three nitrogen atoms, have been prepared and characterized. A method has been devised for introducing an N ‐oxide function into the triazinyl core. Then, by using a Grignard reagent, substitution α to the N ‐oxide group was achieved and the resulting 1,2‐dihydrotriazine‐ N ‐oxide oxidized into the corresponding nitroxide. Solution EPR spectra exhibit hyperfine splitting that confirms spin delocalization over the three nitrogen atoms of the triazinyl ring. They also show that spin delocalization diminishes with increasing distance for the coupling and is largest for nitrogen N1 and weakest for N5. Free radicals 6 a and 13 are stable in the solid state and have been characterized by X‐ray diffraction, but they tend to gradually degrade in solution. In the solid state, these two free radicals are arranged into antiferromagnetically exchange‐coupled pairs, J =−5.2(6) for 6 a and −3.7(4) cm −1 for 13 ( H =−2 JS 1 S 2 ).