ESR Hyperfine Structure in Hydrazyl Free Radicals

Balaban, Alexandrù T.; Marculescu, M.; Pascaru, I.; Rotaru, M.; Valeriu, A.; Weiner, MA

doi:10.1515/zpch-1962-21930

Cited by 14 publications

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“…The most important nitro groups are situated in the ortho -position with regard to the nitrogen atom; thus, between the two 2,4-dinitro and 2,6-dinitro isomers 1 and 2 ( Figure 3 ), there is a huge difference in terms of their stability [ 14 , 15 ]. Accordingly, isomer 1 (2,4-dinitro) can exist only in solution (with a half-life of about 90 h) and not in solid state, while isomer 2 (2,6-dinitro) is stable both in solution and in solid state [ 16 ]. As a consequence, most of the free radicals of such type that contain any other group in position 6 ( para-) are stable [ 4 ].…”

Section: Introductionmentioning

confidence: 99%

The Chemistry of DPPH· Free Radical and Congeners

Ioniță

2021

IJMS

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Since the discovery in 1922 of 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl stable free radical (DPPH·), the chemistry of such open-shell compounds has developed continuously, allowing for both theoretical and practical advances in the free radical chemistry area. This review presents the important, general and modern aspects of the chemistry of hydrazyl free radicals and the science behind it.

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Section: Introductionmentioning

confidence: 99%

The Chemistry of DPPH· Free Radical and Congeners

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2021

IJMS

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“…According to a theory developed by Walter (21), substitution of the hydrogen in the Cposition of the 2,6-dinitrophenyl group in 52-diphenyl-1-(2,6-dinitrophenyl-) hydrazyl by an electron donating group should lead to a decrease in the ratio A,/A,. The ratio is found to decrease from 0.70 (22) to 0.62 for the hydrazyl derived from 1 indicating that the 2,4,6-tri-t-butylphenylthio group acts as an electron donor.…”

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confidence: 93%

Kinetic, Electron Spin Resonance, and Product Studies of the Reaction Between 2,2-Diphenyl-1-picrylhydrazyl and 2,4,6- Tri-t-butylbenzenethiol

Flood¹,

Russell²

1975

Can. J. Chem.

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. Can. J. Chem. 53,1123Chem. 53, (1975. The reaction of 2,2-diphenyl-1-picrylhydrazyl (DPPH) with 2,4,6-tri-t-butylbenzenethiol (TBBT) in benzene solution has been studied. The two major products, 2,2-diphenyl-1-picry1-hydrazine (DPPH-H) and di-(2,4,6-tri-t-butylphenyl) disulfide, are those anticipated for a reaction in which DPPH abstracts hydrogen from the thiol yielding thiyl radicals which undergo coupling to produce the disulfide. About 30% of theDPPH is converted into a derivative in which a nitro group has been displaced by a 2,4,6-tri-t-butylphenylthiyl group. Displacement of NOz from DPPH by the tri-t-butylphenylthiyl radical is thought to constitute an important secondary reaction.In the presence of excess thiol, the rate constant for disappearance of DPPH, determined spectrophotometrically, is 1.23 _+ 0.04 M-' s-I at 25 "C, and the activation energy is 5.8 _+ .0.5 kcal mol-'. The rate of reaction is halved when the thiol is deuterated at the SH group, confirming that the primary step involves hydrogen transfer. Addition of DPPH-H retards the overall reaction indicating that this primary step is reversible. An e.s.r. study of the reacting solutions shows that the concentration of thiyl radical is relatively low until most of the DPPH disappears; it also shows the slow buildup of the 2,4,6-tri-t-butylphenylthiyl derivative of DPPH. The e.s.r. spectrum of the latter derivative has been analyzed and shown to be consistent with nitrogen coupling constants Al = 10.4 + 0.2 G and Az = 6.45 + 0.2 G.JAMES FLOOD et KENNETH E. RUSSELL. Can. J. Chem. 53, 1123Chem. 53, (1975. On a Btudie la reaction du radical diphenyl-2,2 picryl-1 hydrazyle (DPPH) avec le tri-t-butyl-2,4,6 benzene thiol (TBBT) en solution benzenique. Les deux produits majeurs, la diphenyl-2,2 picryl-1 hydrazine (DPPH-H) et le disulfure de di(tri-t-butyl-2,4,6 phenyl) sont ceux attendus pour une reaction dans laquelle le DPPH enleve des atomes d'hydrogtne du thiol amenant la formation de radicaux thiyles qui subissent alors une reaction de couplage pour fournir le disulfure. Environ 30% du DPPH est transforme en un derive dans lequel le groupe nitro a Cte remplad par un groupe tri-t-butyl-2,4,6 phenylthiyle. On croit que le remplacement du NO2 du DPPH par un radical tri-t-butylphCnylthiyle est une reaction secondaire importante.En presence d'un excits de thiol la constante de vitesse pour la disparition du DPPH, tel que determine spectrophotomCtriquement, est de 1.23 , 0.04 M-' s-' a 25 "C et 1'6nergie d'activation est de 5.8 + 0.5 kcal mol-'. La vitesse de la reaction est reduite de moitie quand le thiol est deutkre dans le groupe SH; ceci confirme que 1'Ctape primaire de la reaction implique un transfert d'hydrogene. L'addition du DPPH-H retarde la reaction globale et ceci indique que I'etape primaire est reversible. Une etude r.p.e. des solutions reagissantes montre que la concentration de radical thiyle est relativement basse jusqu'a ce que pratiquement tout le DPPH soit disparu; il montre aussi qu'il y a une accumulation lente du derive tr...

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Selective (15N) nitration of 2,2-diphenyl-1-(2,4- or 2,6-dinitrophenyl)-hydrazines or -hydrazyls

Ioniță

Cãproiu

Luca

et al. 1998

J Label Compd Radiopharm

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Treatment of the title compounds with sodium [15N]nitrite in the presence of crown ether 15‐crown‐5 led to selective nitration yielding 2‐(para‐[15N]nitrophenyl)‐2‐phenyl‐1‐(2,4‐ or 2,6‐dinitrophenyl) hydrazines. When starting from the 2,6‐dinitro‐derivative under the same reaction conditions, a di‐[15N]nitro‐derivative in the para‐phenyl and 4‐positions (picryl) was also obtained. The same reaction carried out with [15N]nitrous acid afforded the same products mentioned above and, in addition when using the 2,6‐disubstituted compound, a tri‐[15N]nitro‐hydrazine in the p,p′, and 4‐positions. The electronic, ESR and NMR spectra of the newly obtained products are presented, and the reaction mechanisms for these unconventional nitrations are discussed. © 1998 John Wiley & Sons, Ltd.

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ESR Hyperfine Structure in Hydrazyl Free Radicals

Cited by 14 publications

References 0 publications

The Chemistry of DPPH· Free Radical and Congeners

The Chemistry of DPPH· Free Radical and Congeners

Kinetic, Electron Spin Resonance, and Product Studies of the Reaction Between 2,2-Diphenyl-1-picrylhydrazyl and 2,4,6- Tri-t-butylbenzenethiol

Selective (15N) nitration of 2,2-diphenyl-1-(2,4- or 2,6-dinitrophenyl)-hydrazines or -hydrazyls

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