Oxidative Coupling during Lignin Polymerization Is Determined by Unpaired Electron Delocalization within Parent Phenylpropanoid Radicals

1996 ◽  
Vol 332 (2) ◽  
pp. 357-366 ◽  
Author(s):  
Wendy R. Russell ◽  
Alex R. Forrester ◽  
Andrew Chesson ◽  
Mark J. Burkitt
Keyword(s):  
Unpaired Electron ◽  
Oxidative Coupling ◽  
Electron Delocalization ◽  
Lignin Polymerization

E.S.R. studies of the oxidative coupling of some bisphenols

1975 ◽  
Vol 28 (2) ◽  
pp. 343 ◽  
Author(s):  
SM Colegate ◽  
FR Hewgill ◽  
GB Howie
Keyword(s):  
Carbon Monoxide ◽  
Alkaline Solution ◽  
Unpaired Electron ◽  
Oxidative Coupling ◽  
Radical Anion ◽  
Neutral Solution

E.s.r. spectroscopy and the identification of products show that oxidation of 3,5,3?,5?-tetra-t-butyl-4,4?-dihydroxybenzophenone in neutral solution gives 3,5,3?,5?-tetra-t-butyldipheno-4,4?-quinone. If oxygen is present 2,6-di-t-butyl-p-benzoquinone is also formed. The evolution of carbon monoxide suggests that bis-spirodienones are intermediate in the formation of these products. E.s.r. spectra of radicals produced by oxidation of 3,5,3?,5?-tetra-t-butylbiphenyl-4,4?- dio and 2,6-di-t-butylhydro-quinone have been re-examined. In alkaline solution 3,5,3?,5?-tetra-t-butyl-4,4?-dihydroxybenzo-phenone is oxidized to a radical anion in which the unpaired electron is delocalized over both rings. ��� Attempts to detect unsymmetrical bisaryloxy radicals were unsuccessful, 3?,5?-di-t-butyl-4,4?-dihydroxy-3,5-dimethoxybenzophenone forming only the radical derived from the syringoyl portion, and 2,4?- oxydiphenol ether forming only the 4?-oxy radical. Comparison with the observation of both radicals when a mixture of guaiacol and p- methoxyphenol was oxidized suggests that C-O-C coupling in 2,4?- oxydiphenol proceeds by direct radical pairing.

Carbocatalytic Acetylene Cyclotrimerization: A Key Role of Unpaired Electron Delocalization

2020 ◽  
Vol 142 (8) ◽  
pp. 3784-3796 ◽  
Author(s):  
Evgeniy G. Gordeev ◽  
Evgeniy O. Pentsak ◽  
Valentine P. Ananikov
Keyword(s):  
Unpaired Electron ◽  
Electron Delocalization

Unpaired electron delocalization in diarylmethane anion-radicals

1972 ◽  
Vol 13 (19) ◽  
pp. 1941-1944 ◽  
Author(s):  
S.P. Solodovnikov ◽  
M.I. Kabachnik
Keyword(s):  
Unpaired Electron ◽  
Electron Delocalization ◽  
Anion Radicals

An Unprecedented Cyano-Induced Sodium Nitrite-Catalyzed C(sp3)-H and C(sp2)-H Coupling Reaction

2018 ◽  
Vol 15 (7) ◽  
pp. 989-994 ◽  
Author(s):  
Ling Li ◽  
Bo Su ◽  
Yuxiu Liu ◽  
Qingmin Wang
Keyword(s):  
Sodium Nitrite ◽  
Oxidative Coupling ◽  
High Resolution Mass Spectrometry ◽  
Coupling Reaction ◽  
13C Nmr Spectroscopy ◽  
Coupling Reactions ◽  
Reaction Conditions ◽  
1H And 13C Nmr ◽  
Oxidative Coupling Reaction ◽  
Oxidative Coupling Reactions

Aim and Objective: During the investigation of sodium nitrite-catalyzed oxidative coupling reaction of aryls, an unprecedented C(sp2)-H and C(sp3)-H coupling of substituted 2-aryl acetonitrile was found. Materials and Methods: The structure of the coupled product was confirmed by 1H and 13C NMR spectroscopy and high-resolution mass spectrometry (HRMS), and comparison of its derivatives with known compounds. The effects of methoxy group in the benzene ring on the reaction were evaluated. Results: The optimized reaction conditions are summarized as follows: CF3SO3H/substrate = 1.5 equiv., NaNO2/substrate = 0.3 equiv., CH3CN as solvent. 2-(4-Methoxyphenyl)acetonitrile and 2-(3,4,5- trimethoxyphenyl)acetonitrile could also generate C(sp2)-H and C(sp3)-H coupling. The coupling reaction occurred as a typical radial mechanism. Conclusion: An unprecedented cyano-induced, NaNO2-catalyzed oxidative C(sp3)-H and C(sp2)-H coupling was reported. The reaction proceeded under very mild conditions, using O2 in the air as terminal oxidant. The unique oxidative manner might provide more inspiration for the development of intriguing oxidative coupling reactions.

Alkyl 1-[2-(oxido anion)-, 3-, 4-, 5-alkyl substituted]phenyl ketyl radicals

1979 ◽  
Vol 44 (6) ◽  
pp. 1731-1741 ◽  
Author(s):  
Andrej Staško ◽  
Ľubomír Malík ◽  
Alexander Tkáč ◽  
Vladimír Adamčík ◽  
Eva Maťašová
Keyword(s):  
Electron Donor ◽  
Unpaired Electron ◽  
Grignard Reagents ◽  
Slight Effect ◽  
Benzene Nucleus ◽  
Alkyl Groups ◽  
Splitting Constant

Reactions of R2,R3-alkyl substituted 2-hydroxybenzenecarboxylic acids 2-HO-C6H2R2-COOH with Grignard reagents R1MgBr in the presence of nickel give stable aryl alkyl ketyl radicals 2-O--R2-, R3-C6H2-CO--R1 where R1 = CH3, C2H5, C2D5, n-C3H7 and R2,R3 = CH3, C2H5, i-C3H7, t-C4H9. The β protons of ketyl group are equivalent (splitting constant 1.25 mT) and non-equivalent (splitting constants within 0.5 to 1.5 mT) for R1 = methyl and other alkyl groups, respectively. Interaction of the γ protons with the unpaired electron was only observed in the case of R1 = n-propyl (splitting constants about 0.07 mT). The substituents R1 have but slight effect on values of splitting constants of the protons in R2,R3 and vice versa. Also splitting constants of the benzene nucleus (a4H = 0.55 mT, a6H = 0.44 mT) are only slightly affected by the substituents R1,R2,R3, which indicates dominant electron-donor effect of the oxido-anion group eliminating the relatively smaller contributions of the alkyl substituents.

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