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
✍ Scribed by Fabian Gerson; Axel Lamprecht; Markus Scholz; Heinz Troxler; Dieter Lenoir
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- German
- Volume
- 79
- Category
- Article
- ISSN
- 0018-019X
No coin nor oath required. For personal study only.
✦ Synopsis
The radical anions of 5H-dibenzo[a,d]cycloheptene (9), 5H-dibenzo[c,fl[ 1,2]diazepine (lo), 5,6-dihydrodibenzo[a,e]cyclooctene (1 l), 5,6-dihydrodibenzo[c,g][ 1,2]diazocine (It), 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 n-system. Whereas the n-spin distribution in the radical anions of the stilbene series is only moderately sensitive to deviations of the n-system from planarity, the radical anions of the azobenzene series respond to steric strain by shifting the n-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 differing ones for their azo counterparts 10'-and 12'-, as well as by the corresponding values for sterically highly hindered 13'-. A plausible interpretation is readily provided by the electron affinities of the constituent n-moieties in stilbene and azobenzene. While those of benzene and ethene are both comparatively low, the azo group has a considerably higher electron affinity. ') Our equipment does not allow the use of the ENDOR technique while the sample is being irradiated.