Radicals 2-thenyl

Trivial names which have found use in this article are thiolane (for tetrahydrothiophene), sulfolane (for tetrahydrothiophene 1,1-dioxide) and sulfolene (for 2,5-dihydrothiophene 1,1-dioxide). As with usual practice, thienyl refers to the radical corresponding to phenyl in benzene chemistry, and thenyl is analogous to benzyl . 

The mechanism of the reaction of thiophene with a variety of radicals as a function of pH has been studied using ESR (81JCS(P2)207). Attack by -OH at pH 6 proceeds by direct addition with a preference to add to the a-position the ratio of (226) to (227) is 4 1. At low pH the (3-adduct easily loses OH- to form the thiophene radical-cation, which may undergo rehydration. In the case of 2-methyIthiophene the radical-cation deprotonates to give the thenyl radical this is reminiscent of the electrochemical oxidation (Section 3.14.2.6). The radical-cations are also formed by direct electron abstraction from the thiophene substrates by chlorine anion-radicals. At pH >6, (226) starts disappearing with formation of ring-opened products (Scheme 61). 

The unit - thiophene linked to a carbon - is termed thenyl, hence thenyl chloride is the prodnct of chloro-methylation (17.1.1.7) thenyl bromides are nsnally made by side-chain radical substitution, snbstitntion at an a-methyl being preferred over a P-methyl." °... 

E.S.R. Spectra.— The e.s.r. spectra of some thienylphenyl and trithienyl-methyl radicals have been analysed. The complex e.s.r. spectrum that arises on treatment of 2,2 -bithienyl with potassium at — 80 °C is interpreted as due to two rotamers of the radical anion of 2,2 -bithienyl. It is believed that the two aromatic rings are held in a planar or nearly planar conformation, where the sulphur atoms are in a cw- or /I a/w-position, for a sufficient time for each rotamer to give an individual spectrum. 2-Phenyl-thiophen is claimed to behave similarly. The ketyls from thiophen-2-aldehyde and 2-acetylthiophen also give overlapping spectra, assigned to the 0-cis- and O-frawj -isomers present in unequal amounts. Well-resolved e.s.r. spectra of the 2- and 3-thenyl and 5-methyl-2-thenyl radicals, produced by the reaction of t-butoxyl radicals with the methylthiophens, were also obtained, and the spin distributions in the radicals studied were compared... 

At the present time, attempts are being made to expand the circle of amines for practical use. Thus, it was shown in [27] and [28] that certain secondary amines of the thiophene series, the S3mthesis of which is more accessible than that of amines of the benzene series, possess good stabilizing properties (as applied to rubbers and polyolefins). Moreover, the replacement of the phenyl radical in the molecule of phenyl-/3-naphthylamine by the thenyl radical in a number of cases exerts a more favorable influence on the effectiveness of the amine. For example, 2-thenyl-/3-naphthylamine is not inferior to neozone D ineffectiveness, and sometimes surpasses it. The effectiveness of the amine is substantially increased if a hydroxyl group is introduced into the molecule. The introduction of an OH group into the molecule of diphenylamine [29] increases the effectiveness of the latter. An analogous picture is observed with amines of the thiophene series [28]. 

Spin echo techniques have been used successfully to demonstrate the 1-D electron spin transport in highly anisotropic organic conductors [27,29]. Such studies have been carried out on single crystals, e.g., fluoran-thenyl radical cation salts. The anisotropy of spin diffusion is deduced from the time constants of the echo signal decay for the gradient field parallel and perpendicular to the chains. 

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