The ESR spectrum of the cis-stilbene radical anion

Gerson, Fabian; Ohya-Nishiguchi, Hiroaki; Szwarc, M.; Levin, G.

doi:10.1016/0009-2614(77)80515-0

Cited by 31 publications

(35 citation statements)

References 15 publications

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“…On the other hand, the (Z)-configuration of both 3 and 4 can be fixed by a CH, or a CH,CH, group linking ortho -positions of the Ph substituents. Such a bridging yields 5H-dibenzo [ In the present work, we reinvestigated 9'- [8] [14] with the use of ESR, ENDOR, and general-TRIPLE-resonance spectroscopy and applied these techniques to lO'--lZ.-. Our studies also include the radical anion obtained from (E)-and (Z)-2,2,5,5-tetramethyl-3,4-diphenylhex-3-enes ( = 1,l'-[ 1,2-bis( l,l-dimethylethyl)ethene-l,2-diyl]bis(benzenes); 13 and 14), in which the bulky tert-butyl substituents at the central C=C bond of 1 and 3 force the Ph groups into positions almost perpendicular to this bond.…”

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confidence: 99%

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

Gerson¹,

Lamprecht²,

Scholz³

et al. 1996

Helvetica Chimica Acta

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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.Introduction. -The isoelectronic (E)-stilbene (1) and (E)-azobenzene (2) belong to the basic organic compounds of which radical anions were first investigated by ESR spectroscopy 30 years ago [l-31, and which have since been repeatedly studied by ESR and ENDOR techniques [4][5][6]. Due to the pronounced electron affinity of the azo group, the half-wave potential of 2 (-1.38 V vs. SCE [6]) is markedly less negative than that of 1 (-2.22 V [7]). Despite this difference, the radical anions 1'-and 2'-have a similar 71-spin distribution which is evidently governed by the same topology of their 71 -systems. It may, however, be argued that this distribution will be affected differently by deviations of the 71-system from planarity.Conversion of 1 and 2 into their corresponding (2)-isomers 3 and 4 is a straightforward way to increase such deviations. Both radical anions, 3'-and 4'-, are not persistent because they rapidly isomerize to 1'-and 2'-, respectively. Nevertheless, 3'-could be

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confidence: 99%

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

Gerson¹,

Lamprecht²,

Scholz³

et al. 1996

Helvetica Chimica Acta

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“…Gerson has observed the same phenomenon in the esr spectra of various radical anions containing the T-system of cis-stilbene (e.g., cis-stilbene itself (12), and 1,2-diphenyl-cyclobutene (12), -cyclopentene (1 3), and -cyclohexene (4?) (14); this last compound is conformationally closely related to our diphenyldioxene l~: ) .…”

Section: Resultsmentioning

confidence: 63%

“…A similar The tentative assignment of the hyperfine coupling constants in l c + is based on the assumption that a(H,,)/a(H,,) = ca. 4.2 (here it is 4.2), and on Gerson's analysis of the spectra of the radical anions related to cis-stilbene, particularly his argument that, in this context, steric hindrance leads to a reduction in the absolute value of an a-proton coupling constant (12)(13)(14).…”

Section: Resultsmentioning

confidence: 98%

The electron spin resonance spectra of dioxene radical cations

Davies¹,

Shields²,

Evans³

et al. 1989

Can. J. Chem.

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. Can. J. Chem. 67, 1748 (1989).The electron spin resonance spectra of the radical cations of dioxene (la), 2,3-dimethyldioxene (lb), 2,3-diphenyldioxene (lc), and benzodioxane (2) in fluid solution have been observed and analysed, with the help of ENDOR spectroscopy in the case of l c . It is concluded that in l c the molecule has overall C2 molecular symmetry. In all four compounds, the pseudo-axial and pseudo-equatorial protons of the methylene groups in the half-chair dioxene rings are distinguished by different hyperfine coupling constants, and simulation of the spectra over a range of temperatures has given the Arrhenius parameters for the ring inversion of l a , l b , and 2.

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“…A comment on the assignments of coupling constants to a-protons in the ortho-positions of the two Ph groups is here in place. For all radical anions containing the n-system of (Z)-stilbene, the four protons in these positions are only pairwise equivalent ([I] [7] and Tables I and 2 in the present work). Typically, the coupling constants of the two pairs amount to -0.291 and -0.194 mT for the radical anion of (2)-stilbene [l] (signs according to theory) and to -0.271 and -0.195 mT for 6-at 273 K. The (absolutely) larger value has generally been assigned to the pair of protons in the outward ortho-positions (o in the present notation), leaving the smaller one for that in the inward positions (0').…”

Section: 4-diphenyl-8-oxabicyclo[43o]non-3-ene (5)mentioning

confidence: 97%

“…The protons attached to the two Ph groups (a protons) are designated o and 0 ' at the ortho-, m and m' at the meta-, andp at the para-positions, whereby the presence and the absence of the 'dash' refer to the inward and outward locations, respectively. Assignments of the coupling constants to individual pairs of equivalent protons in 4' are based on comparison with the hyperfine data for structurally related radical anions of 1, 2, 3 [l], and (Z)-stilbene [7]. The signs of these coupling constants (Table 1) have been determined by the general TRIPLE resonance technique [8] with aH@), aHio), and aH(o.)…”

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confidence: 99%

The Radical Anions of 1,2‐diphenylcyclohexene and Structurally Related Compounds. Conformational ESR and ENDOR studies

Gerson

Martin

1987

Helvetica Chimica Acta

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ESR, ENDOR, and TRIPLE resonance studies have been performed on the radical anions of 1,2-diphenylcyclohex-I-ene (4), I ,2-di(perdeuteriophenyl)cyclohex-l-ene ((D,,,)4), the frans-configurated 3,4-diphenyl-S-oxabicyclo[4.3.0]non-3-ene (5) and its 2,2,5,5-tetradeuterio derivative (D4)5, and 2,3-diphenyl-S,9,IO-trinorborn-2-ene (6).The spectra of 4' exhibit strong temperature dependence along with a specific broadening of ESR hyperfine lines and proton ENDOR signals. The coupling constant, which bears the main responsibility for these features, is that of theb-protons in the quasi-equatorial positions of the cyclohexene ring, and the experimental findings are readily rationalized in terms of relatively modest conformational changes without invoking the inversion of the half-chair form. The hyperfine data for the /3-protons in 5' closely resemble the corresponding low-temperature values for 4'. However, the 'unusual' features observed for 4' are absent in the ESR and ENDOR spectra of 5-, because the half-chair conformation of the cyclohexene ring in 5: is deprived of its flexibility. Although the boat form of this ring in 6' is also rigid, the spectra of 6' are temperature-dependent, due to an interconversion between two propeller-like conformations of the phenyl groups. The pertinent energy barrier is 30 & 5 kJ 'mo1-l. An analogous interconversion presumably takes place in 4' and 5' as well, but, unlike 6', it is not amenable to experimental study.

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The ESR spectrum of the cis-stilbene radical anion

Cited by 31 publications

References 15 publications

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

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

The electron spin resonance spectra of dioxene radical cations

The Radical Anions of 1,2‐diphenylcyclohexene and Structurally Related Compounds. Conformational ESR and ENDOR studies

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