Rearrangement with 1,2-migration of chlorine in reaction of p-methylbenzyl radicals with 3,3,3-trichloropropene

Conclusions The reaction of p-xylene with 3,3,3-trichloropropene, initiated by peroxides, leads to the formation of 1,1-dichloro-4-(p-tolyl)-1-butene, 1,1,2-trichloro-4-(p-tolyl)butane, and 1,1-dichloro-2-chloromethyl-3-(p-tolyl)propane, which testifies to a rearrangement of the CCl₃HCH₂CH₂C₆H₄CH₃ radicals to the C1₂CHCI-CH₂ CH₂C₆H₄CH₃ radicals with the 1,2-migration of chlorine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2122–2124, September, 1976.     

35Cl NQR study of CCl3 reorientations in the carbonyl-containing derivatives of 3,3,3-trichloropropene

Temperature dependences of³⁵Cl NQR frequencies and spin-lattice relaxation times were measured for the CCl₃ groups of compounds CCl₃CH=CHR and CCl₃CH=CR₂ with R=COCH₃ and COOCH₃. The activation energies of CCl₃ reorientations reflect the significant contribution of intermolecular steric interactions to the value of the potential barrier hindering these reorientations. In the CCl₃CH=CHCOCH₃ crystal, the reorientations of the CCl₃ group are hindered more than those of the molecule as a whole. Perm State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 2, pp. 54–60, March–April, 1994. Translated by L. Smolina     

Regioselectivity in free radical bromination of unsymmetrical dimethylated pyridines

During a literature review some curious inconsistencies in the free radical bromination of picolines were noted. To achieve a better understanding of the mechanisms and regioselectivity we reran these reactions, extending our work to unsymmetrical lutidines using N-bromosuccinimide in limiting amount. Characterization of the products was done with GC/MS and H NMR. The regioselectivity of bromination in unsymmetrical dimethylpyridines shows that nitrogen in the ring is deactivating inductively. The competition between 2,3, 2,4, and 2,5 dimethyl pyridine toward bromination results with bromination in the methyl group farthest from the N in the ring. 3,4-Lutidine shows only the 4,4-dibrominated product.     

An unusual radical Smiles rearrangement

Radicals derived from N-(alpha-xanthyl)acetanilides or N-(alpha-xanthyl)acetylaminopyridines possessing a substituent next to the nitrogen undergo a hitherto undocumented Smiles rearrangement proceeding through a four-membered ring. It was also found that under certain conditions the amidyl radical produced by cleavage of the four-membered ring intermediate can undergo fragmentation to give an isocyanate. Such fragmentations are unprecedented at temperatures corresponding to refluxing benzene or chlorobenzene. [reaction: see text]     

Direct observation of aminyl radical intermediate during single-crystal to single-crystal photoinduced Orton rearrangement

A photoinduced analogue of the thermal Orton rearrangement reaction by which an N-chlorine atom from a side amino group is transferred to a phenyl ring was studied in the solid state. Contrary to the mixture of products obtained in solution, in the N-chloro-N-acetylaminobenzene crystals the photoreaction proceeds with complete preservation of crystallinity, affording selectively and quantitatively the para isomer of chloroacetanilide. Study of the reaction mechanism by in situ steady-state photodiffraction, a combination of photoexcitation by UV light and single-crystal X-ray diffraction analysis, provided evidence for creation of N-acetyl-N-phenylaminyl (AcPhN*) radical as a metastable reaction intermediate. The structure of the aminyl radical produced in 9.2% yield from the major disordered component in the statically 85.6:14.4 disordered crystal was directly observed for the first time. The unprecedented stability of the radical is prescribed to the solid-state cage effect, the reactive center of the radical species being locked away from the reactive target molecules. The creation of the radical and its head-to-tail chain reaction within the undulated hydrogen-bonded ribbons involving the acetyl carbonyl group are employed to explain the high selectivity of the photoinduced single-crystal to single-crystal Orton rearrangement. On the basis of the change of the crystal structure and the physicochemical data, a three-center five-atom mechanism involving homolytic cleavage of the N-Cl bond followed by hydrogen abstraction by the carbonyl group is suggested for the solid-state photoinduced Orton rearrangement.     

钝化芳环的溴化反应研究

研究了钝化芳环的溴化方法，对三氟甲基苯等一系列含有不同钝化基团的芳环 化合物用KBrO3-H2SO4直接溴化，取得了良好的结果。对影响该反应的因素，如硫 酸的浓度和用量、反应温度和不同钝化基团的影响等进行了分析。     

The radical cation of syn-tricyclooctadiene and its rearrangement products

The syn dimer of cyclobutadiene (tricyclo[4.2.0.0(2.5)]octa-3,7-diene, TOD) is subjected to ionization under different conditions and the resulting species are probed by optical and ESR spectroscopy. By means of quantum chemical modelling of the potential energy surfaces and the optical spectra, it is possible to assign the different products that arise spontaneously after ionization or after subsequent warming or illumination of the samples. Based on these findings, we propose a mechanistic scheme which involves a partitioning of the incipient radical cation of TOD between two electronic states. These two states engage in (near) activation-less decay to the more stable valence isomers, cyclooctatetraene (COT*+) and a bis-cyclobutenylium radical cation BCB*+. The latter product undergoes further rearrangement, first to tetracyclo[4.2.0.0(2,4).0(3,5]oct-7-ene (TCO*+) and eventually to bicyclo[4.2.0]octa-2,4,7-triene (BOT*+) which can also be generated photochemically from BCB*+ or TCO*+. The surprising departure of syn-TOD*+ from the least-motion reaction path leading to BOT*+ can be traced to strong vibronic interactions (second-order Jahn-Teller effects) which prevail in both possible ground states of syn-TOD*+. Such effects seem to be more important in determining the intramolecular reactivity of radical cations than orbital or state symmetry rules.