Equilibrium studies by electron spin resonance. I. Free nitrobenzene anion radical

Stevenson, Gerald R.; Echegoyen, Luís; Lizardi, Luis R.

doi:10.1021/j100654a012

Cited by 32 publications

(21 citation statements)

References 3 publications

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“…The magnitude of a M is shown to decrease on going from sodium to potassium, becoming vanishingly small for the lithium counterion. This is the normal trend observed for the ion pairs of nitrobenzenides [4][5][6] whose structure is characterized by having the metal located in the neighborhood of the oxygen atoms of the nitro group: the larger cation above the plane of the NO 2 and midway between the oxygen atoms, the smaller one localized at either of the two oxygen atoms. 5 According to this, the magnitude of a M seems not to be linked to any definite physical quantity of the metal because it is the result of a balance between negative and positive spin densities created by different mechanisms of spin-transfer onto the diamagnetic cation.…”

Section: Resultsmentioning

confidence: 53%

“…Stevenson and his coworkers, considering the solvent perturbation to be negligible, have calculated the contribution of cation perturbation to a N of alkali-metal-nitrobenzenide ion pairs in HMPA. 4 The value they obtained for the ion pair of Na, by subtracting a N of free ion from a N of ion pair, is 2.5. According to this, it is interesting that also for 7-NBTZ ·-Na + ion pair I find exactly the same contribution of cation perturbation to a N (NO 2 ), even though the coupling constants utilized for the calculation in this case are measured in different solvents: THF for the ion pair [a N (NO 2 ) = 10.12 G] and HMPA for the free ion (a N (NO 2 ) = 7.63 G).…”

Section: Resultsmentioning

confidence: 97%

“…6 Stevenson et al generated the radical anion of nitrobenzene by reduction with alkali metals in HMPA, a solvent with powerful solvating ability for alkali metal ions, and detected ion pairs and free ions simultaneously. 4 Moreover, they found that the residual tendency for nitrobenzenides to form ion pairs in this solvent decreases when electron-withdrawing groups are present in the para position. 7 Applied to nitrobenzothiazoles, the reduction with Na in HMPA afforded the corresponding radical anion only in the case of 7-NBTZ.…”

Section: Resultsmentioning

confidence: 99%

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Radical anions of nitrobenzothiazoles. II. EPR study of free radical anions and ion pairs

Ciminale¹

2006

Arkivoc

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The paramagnetic species produced by reduction of the title compounds (NBTZ) with different reducing agents have been characterized by EPR spectroscopy. Radical ion pairs were observed upon reduction with alkali metals (Li, Na, K) in THF only from 5-, 6-, and 7-nitrobenzothiazole. The free radical anion of 7-NBTZ was obtained by reduction with Na in HMPA. Different tetraethylammonium ion pairs of the radical anion of 7-NBTZ were detected in HMPA when the reduction was performed by electrolysis at variable concentration of tetraethylammonium perchlorate as supporting electrolyte.

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Section: Resultsmentioning

confidence: 53%

Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Radical anions of nitrobenzothiazoles. II. EPR study of free radical anions and ion pairs

Ciminale¹

2006

Arkivoc

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“…(There are at least 11 unique proton and 3 unique nitrogen couplings possible; see SI for the entire EPR spectrum , We surmised that the smallest couplings observed come from the small amount of unpaired electron spin residing in the π system of the phenyl ring attached to N1. Therefore, efforts were undertaken to simplify the EPR spectrum through replacement of this phenyl ring with the perdeuteriated analog.…”

Section: Resultsmentioning

confidence: 99%

Influence of Annulation on the Electron Spin within the 1,2,3-Triazole Ring in Annulenotriazole Anion Radicals

Peters

Maybell

2018

J. Org. Chem.

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The low temperature (-100 °C) single electron reduction of N1-phenylbenzotriazole in liquid ammonia, and the room temperature reduction of N1-phenylcyclooctatetraenotriazole in hexamethylphosphoramide, yields stable solutions of both anion radicals, which were studied via EPR spectroscopy. The amount of electron spin localized within the triazole ring, and how spin is distributed within this ring, is greatly influenced by the size of the annulene ring attached. UB3LYP/6-31++G(d,p) geometry optimizations using DFT methods were carried out for both anion radicals, and the calculated coupling constants (and electron spin densities) are in good agreement with the EPR spectroscopic results. Both theory and experiment show that much of the unpaired electron spin in the N1-phenylbenzotriazole anion radical is delocalized over the entire π system of benzotriazole ring including the phenyl ring attached, but that a significant percentage of total spin is found to reside within triazole ring with much of it located on the second nitrogen (N2). With the N1-phenylcyclooctatetraenotriazole anion radical, the majority of spin is localized over the π system of the COT ring, however a relatively small amount of total spin, found within the triazole moiety, is largely concentrated on two of the nitrogens (N1 and N3) within the ring.

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“…To see if the compound with the highest solution electron affinity (presumably 3 ) could be trapped as its corresponding radical anion and observed by EPR spectroscopy (as was [8]annulyne), dehydrated hexamethylphosphoramide (HMPA)8a,b was distilled into the C 6 D 6 solution. Subsequently, the 50:50 HMPA/C 6 D 6 solution was briefly exposed to a potassium metal mirror yielding a paramagnetic solution.…”

Section: Methodsmentioning

confidence: 99%

The Isomers of [12]Annulyne and their Reactive Relationships to Heptalene and Biphenyl

2008

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The colorful and interesting chemistry of the annulenes represents a still living vestige ("Renaissance of Annulene Chemistry") [1] of the days of the intense investigation of small hydrocarbon ring systems.[2] The smallest possible "antiaromatic" dehydrogenated annulene, [8]annulyne, [3] can be trapped as its radical anion, thus avoiding destabilization due to the p-electron count rule, and can be studied by EPR spectroscopy.[3] The situation turns out to be much more complex and intriguing in the case of the [12]annulyne system.[12]Annulyne, which can be thought of as the double ring expanded o-benzyne, [4] is the smallest "antiaromatic" annulyne (4n p-electrons) capable of isomerization and having internal protons. The [12]annulynes are also subject to destabilization from the p-electron count rule, but upon one-electron reduction they undergo, much to our amazement, rearrangement to form either the radical anion of biphenyl or of heptalene, depending upon the particular isomer being reduced.It was recently reported that the facile base condensation of 1,5-hexadiyne with potassium tert-butoxide in tetrahydrofuran (THF) leads directly to the formation of two isomers of [12]annulyne: [5] 5,10-di-int-di-trans-[12]annulyne (1) and 4,11-di-int-di-trans- [12]annulyne [6] (2) in a 1:1 ratio (Scheme 1).Since the products from the base condensation of hexadiyne vary with ion association conditions, [7] we thought that we might be able to establish the conditions whereby the remaining possible symmetrical isomers of [12]annulyne (6,9-di-int-di-trans- [12]annulyne and the all cis-[12]annulyne) would be revealed.1,5-Hexadiyne was exposed to a mixture of potassium tertbutoxide and [18]crown-6 in an evacuated sealed apparatus using the same procedure that produced 1 and 2, [5] except that the [D 8 ]THF solvent system was replaced with perdeuterated benzene. Cooling an attached NMR sample tube causes the C 6 D 6 and any volatile products to cleanly distill into the tube, which can subsequently be sealed from the apparatus. The now clear, colorless, freshly distilled C 6 D 6 solution exhibits a 1 H NMR signal revealing two new C 12 H 10 isomers: 3 (6,9-diint-di-trans-[12]annulyne) and 4 (a cumulene structure with four additional cis double bonds) (Figure 1). The "impurity" signal at d = 5.6 ppm is greatly diminished as is the ratio [3]/[4] when the solution is distilled through a column warmed to 150 8C. These products are clearly kinetically controlled and ion association, in the intermediates, plays a role.The internal protons of 3 appear at d = 6.99 ppm. This is close to the conventional aromatic region for benzenoid systems, which suggests some paratropicity. Downfield shifts were also observed for the internal protons of 1 and 2 at d = 6.87 and 6.63 ppm, respectively. The paratropic shifts are not as prominent in 4, because the C À C bond angle strain prevents the approach to planarity.The requirement that the larger three bond J couplings apply across a true double bond demands that compound 4 be 1 H NMR spectrum (2...

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Equilibrium studies by electron spin resonance. I. Free nitrobenzene anion radical

Cited by 32 publications

References 3 publications

Radical anions of nitrobenzothiazoles. II. EPR study of free radical anions and ion pairs

Radical anions of nitrobenzothiazoles. II. EPR study of free radical anions and ion pairs

Influence of Annulation on the Electron Spin within the 1,2,3-Triazole Ring in Annulenotriazole Anion Radicals

The Isomers of [12]Annulyne and their Reactive Relationships to Heptalene and Biphenyl

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