E. S. Klimov

One-electron oxidation and triphenylmethylation of benzimidazolines by the triphenylmethyl cation

With triphenylmethyl perchlorate (tetrafluoroborate) 1, 2, 2, 3-tetrasubstituted benzimidazolines undergo electrophilic triphenylmethylation at position 5. In further reaction with the electrophilic agent the obtained 5-triphenylntethylbenzimidazolines are converted into radical-canons. They undergo a similar transformation during the action of silver perchlorate and molecular oxygen. The results from investigation of the radicalcations by ESR and PMR are given.

Oxidation-reduction characteristics of octahydrochalcogenoxanthenes and octahydroxanthylium cations

Unstable radical-cations, which fragment according to the (−e, −H+, −e) scheme, are formed during the electrochemical oxidation of chalcogenooctahydroxanthenes. Free radicals (identified by ESR) are formed during the electrochemical reduction of the chalcogenooctahydroxanthylium cations.

Investigation of the reaction of 1,2,3-trimethyl-2-phenylbenzimidazoline with dehydrogenating reagents by EPR spectroscopy

The reaction of 1,2,3-trimethyl-2-phenylbenzimidazoline with a number of reagents that manifest dehydrogenating properties with respect to benziraidazolines was studied by EPR spectroscopy. These reagents convert 1,2,3-trimethyl-2-phenylbenzimidazoline to a relatively stable cation radical. The mechanism of the dehydrogenation of benzimidazolines is discussed taking into account the established facts.

Electron transfer as the initiating stage of dehydrogenation of benzimidazolines by the triphenylmethyl cation

We consider a radical-ion mechanism for dehydroaromatization of benzimidazolines by triarylmethyl cations, including as the initial step electron transfer from the hydroheteroaromatic compound to the electrophilic reagent. We draw the conclusion that there is significant weakening of the C(2)-H bond in the benzimidazoline radical cation formed in this stage.

ESR spectra of sterically hindered silicon-containing phenoxyls

The ESR method was used to study a series of sterically hindered silicon-containing phenoxyls — 2-trialkyl(dialkylalkoxy)silyl-4,6-di-tert-butylphenoxyls. The parameters of the ESR spectra were determined: the constants of splitting of the unpaired electron on meta-protons of the phenoxyl ring, protons of the organosilyl substituents, and magnetic silicon nuclei, as well as the spectroscopic splitting factors. The stability of the silicon-containing phenoxyls relative to one another was determined. The influence of a second Si-containing substituent in the ortho-position and an alkyl substituent in the para-position was followed on the example of 2,6-triphenylsilyl-4-tert-butylphenoxyl and the 2,6-trimethylsilyl-4-ethylphenoxyl radical. The stability of the aroxyls is determined primarily by the steric shielding of the radical site responsible for the dimerization-rearrangement reaction.

1,1′,2,2′,6,6′-Hexaphenyl-4,4′-bipyridinium cation radical

Aniline reacts with 2,2′,6,6′-tetraphenyl-4,4′-bipyrilium perchlorate to form 1,1′,2,2′,6,6′-hexaphenyl-4,4′-bipyridine perchlorate. A relatively stable cation radical is formed in the first stage of electrochemical reduction of this compound, which has been examined by ESR, where there are splittings from two nitrogen nuclei and the four protons in the 3,3′,5,5′ positions: aN=0.38; aH=0.14 mT.

2,6-di-tert-butyl-4-perimidylphenols and their oxidation

Abstract1,8-Naphthylenediamine was reacted with 2,6-di-tert-butyl-4-formyl-phenol to produce 2,6-di-tert-butyl-4-(1,3-dihydro-perimidyl) phenol (I). The latter was coverted into 2,6-di-tert-butyl-4-(1H-perimidyl)phenol (II) by oxidizing I with sodium pyrosulfate. When phenol II was oxidized by lead dioxide in toluene and THF, the EPR spectra revealed a 12-component multiplet with perimidyl splitting constants a1N=a3N=aHNH=0.2 mT; aH6.7=0.6 mT.

OXIDATIVE CLEAVAGE OF THE C-C BOND IN PROCESSES INVOLVING THE HETEROAROMATIZATION OF 9R-SYM-NONAHYDRO-10-OXA(CHALCOGENA)ANTHRACENES

The reaction of 9-(2-methoxyphenyl)- and 9-(2-thienyl)-sym-nonahydro-10-selena(thia)anthracenes with trifluoroacetic acid causes their heteroaromatization with the elimination of substituents from the γ positions of the heterorings. A similar transformation of these compounds, as well as their oxygen and 9-benzyl-substituted analogs, occurs during anode electrochemical oxidation. The stepwise character of the cleavage of the C-C bond, which includes one-electron oxidation of the chalogenapyrans and subsequent fragmentation of the cation-radical intermediates, is substantiated.

Free radicals in redox reactions of 4,4′-di-(2,6-diphenylthiapyrylo)monomethinecyanine fluoroborate

ESR spectroscopic and electrochemical studies of the one-electron reduction and oxidation of 4,4′-di-(2,6-diphenylthiapyrylo)monomethinecyanine have been carried out. Relatively stable cyanine free radicals have been detected and characterized.

Influence of the conjugate anion on the parameters of ESR spectra in radical cations of sterically hindered hydroquinones

The reactions of hindered p-quinones and hydroquinones with inorganic, organic, and Lewis acids have been studied by ESR. The conjugate anion has a strong perturbing effect on the distribution of the spin density at the reaction center. A mechanism for the reduction of p-quinones and the oxidation of hydroquinones, which includes a step involving the formation of radical-cation salts, has been proposed. The form of the ESR spectra and the composition of the final products are greatly dependent on the ratio between the reactants, the medium, and the temperature.