15464-00-3Relevant academic research and scientific papers
Electron Spin Resonance Study of Azoalkane and Imine Radical Cations
Rhodes, Christopher J.
, p. 3215 - 3222 (2007/10/02)
Radical cations of azoalkanes have been observed for the first time in low-temperature matrix by e.s.r. spectroscopy.The e.s.r. data show that they are ?-cations despite photoelectron studies which indicate the HOMO for an azoalkane to be the ? (n-) orbital.Interestingly, these species appear to be stable, at least up to ca. 160 K, and show no tendency to fragment to form alkyl radicals.This contrasts with the solution-phase behaviour of these species, which are intermediates in the oxidation of azoalkanes, and give rise to carbocations and alkyl radicals.Imines form similar ?-radical cations which show a greater tendency to decompose.The structures and stabilities of these cations are discussed.Attempts to observe the corresponding azoalkane anions in solid matrices resulted only in the formation of alkyl radicals, and so we conclude that the anions decompose by fragmentation, although they have been studied in solution under steady-state conditions.Previously derived coupling parameters predict isotropic 14N hyperfine couplings for these species which are larger than those observed.Therefore, new values are calculated, and these fit well with the observed couplings.In this way, spin polarisation parameters are obtained for individual contributions to the couplings, as opposed to previous approaches which treat them collectively.
Triaziridines. Ring Openings of Triaziridines
Hipert, Hans,Dreiding, Andre S.
, p. 277 - 291 (2007/10/02)
Eleven triaziridine derivatives were heated at 60 deg C in CDCl3 to obtain information on the tendency towards, resp. the resistance to, ring opening of the N3-homocycle by thermolysis.Among these triaziridines, there are three which contain, as one of the substituents, a methoxycarbonyl group (ester derivatives 1, 5, and 16), three a methyl group (methyl derivatives 18, 24, and 26), three an H-atom (14, 27, and 30), and two a negative charge (31 and 32).The other two substituents in each of these four classes of triaziridines are trans-located i-Pr groups (1, 18, 27, and 31), cis-located i-Pr groups (5, 24, 14, and 32), and a 1,3-cis-cyclopentylidene group (16, 26, and 30).As major products of these mild thermolyses, we isolated: from the trans-ester 1 and from the annellated ester derivative 16, the 1-acyl-azimines 2 and 17, respectively, from the cis-ester 5, the 3-acyl-triazene 4, from the trans-methyl derivative 18, the (E)-diazene 19 and hexamine 21, from the cis-methyl derivative 24 the 2-methylazimine 25, both from the trans- and cis-H-derivatives 27 and 14, respectively, the H-triazene 13 and, finally, both from the trans- and cis-anion 31 and 32, respectively - after protonation - the H-triazene 13 and - after methylation - the methyl-triazene 33.The same thermolysis of the annelated methyl and H-derivatives 26 and 30, respectively, resulted only in decomposition.These results can be uniformly interpreted with a primary opening of the triaziridine ring by rupture of one of the two types of N-N bonds leading to azimines or triazenide anions.Some of the azimines were isolable, namely 2, 17, and 25, and one was spectroscopically observable as an intermediate, namely 11 on the way to the triazene 4.The other azimines are plausible intermediates to the isolated products, namely 15 on the way to 13, and 22 on the way to 19 and 21.The triazenide anion 28 is the evident intermediate on the way to 13 or to 33.The annelated azimines are assumed not be formed from 26 and 30, or then to be decomposed under the conditions of their formation.We conclude that the triaziridine derivatives 1, 16, and 18 underwent thermal ring opening between N(1) and N(2), while the derivatives 5, 14, 24, 27, 31, and 32 were ruptured between N(2) and N(3); no conclusion was possible on the ring opening of the derivatives 26 and 30.The predominant formation of the (Z)-azimine 2 from the trans-triaziridine 1, and of the (E)-isomer 3 - among the two azimines - from the cis-triaziridine 5 suggests a stereospecificity in the triaziridine ring openings.This would, however, not be expected to be observable in the products from the other triaziridines, since both N-N bonds of the azimine 25 and of the anion 28 probably rotate rapidly and since the secondary transformations of the other primary products are not able to retain configurational information.
