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Effect of non‐planarity on the spin distribution in the radical anions containing the stilbene or the azobenzene π‐system: An ESR and ENDOR Study
Author(s) -
Gerson Fabian,
Lamprecht Axel,
Scholz Markus,
Troxler Heinz,
Lenoir Dieter
Publication year - 1996
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.19960790130
Subject(s) - chemistry , azobenzene , planarity testing , photochemistry , spin (aerodynamics) , distribution (mathematics) , crystallography , organic chemistry , molecule , mathematical analysis , mathematics , engineering , aerospace engineering
The radical anions of 5 H ‐dibenzo[ a,d ]cycloheptene ( 9 ), 5 H ‐dibenzo[ c,f ][1,2]diazepine ( 10 ), 5,6‐dihydrodibenzo[ a,e ]cyclooctene ( 11 ), 5,6‐dihydrodibenzo[ c,g ][1,2]diazocine ( 12 ), and ( E )‐2,2,5,5‐tetramethyl‐3,4‐diphenylhex‐3‐ene ( 13 ) were characterized by ESR and ENDOR spectroscopy. Their hyperfine data were compared with those previously reported for radical anions also containing the stilbene or the azobenzene π‐system. Whereas the π‐spin distribution in the radical anions of the stilbene series is only moderately sensitive to deviations of the π‐system from planarity, the radical anions of the azobenzene series respond to steric strain by shifting the π‐spin population from the benzene rings to the azo group. This finding is impressively demonstrated by the similar hyperfine data for 9 · − and 11 · − which contrast with the strongly highly hindered 13 · − . A. plausible interpretation is readily provided by the electron affinities of the constituent π‐moieties in stilbene and azobenzene. While those of benzene and ethene are both comparatively low, the azo group has a considerably higher electron affinity.