Eric S. Turner

The molecular structures of O-methylhydroxylamine, N-methylhydroxylamine, N,O-dimethylhydroxylamine and N,N,O-trimethylhydroxylamine in the gas phase, determined by electron diffraction

Abstract The molecular structures of O -methylhydroxylamine, N -methylhydroxylamine, N , O -dimethylhydroxylamine and N , N , O -trimethylhydroxylamine in the gas phase have been determined by electron diffraction. In each case, the principal conformer present had the anti conformation about the N-O bond, but the dimethyl- and trimethyl-hydroxylamines also had 20–30% of the syn conformer. The N-O bond lengths increase with methyl substitution, from 146.3(3) pm in NH 2 OMe to 151.3(9) pm in Me 2 NOMe; C-N bond lengths also increase, but C-O bond lengths show a decrease.

The conformational analysis of tetrahydro-1,4,2-dioxazines

Abstract A conformational study of some tetrahydro-1,4,2-dioxazines by use of 1 H and 13 C NMR spectroscopy is reported. The conformational characteristics of this ring are compared to those of the related systems, tetrahydro-1,2- and 1,3-oxazine. A study of model compounds allows the assignment of ring and nitrogen inversion processes in the variable temperature NMR spectra. Ring inversion is found to be a lower energy process than nitrogen inversion. The barriers to these processes are measured in several derivatives and the implications of the results for studies of nitrogen inversion in other 6-membered rings are pointed out. The conformational free energy differences of N-Me and N-Et groups are measured and discussed. It is somewhat easier to put an N-Et group axial than N-Me ( ca .0.25 kcal mole −1 ). It also appears than an Et group at C-6 goes axial more readily than does a Me.

Barriers to nitrogen inversion in 6-membered rings : Nitrogen inversion in tetrahydro-1,2-oxazines

Abstract A study of the nitrogen inversion process in the bicyclic oxazine, N-methyl-2-oxa-3-azabicyclo[2,2,2]octane, by 13 C NMR spectrocopy reveals a free energy of activation of 14.9 kcal mole -1 . Detailed examination of the kinetics of the process observed in the 1 H spectra of N-methyl tetrahydro-1,2-oxazine shows ΔH ≠ 15.1±0.4 kcal mole -1 and ΔS ≠ 2.3 ±1.5 cal mol -1 K -1 . It is concluded from the similarity in the activation parameters that both processes arise from nitrogen inversion.

The synthesis and conformational analysis of tetrahydro-1,2,4-oxadiazines

Abstract The synthesis and variable temperature 1 H and 13 C NMR spectra of three tetrahydro-1,2,4-oxadiazines are reported. The N(4)-Me inversion barriers are 6.8–7.0 (ax→ts) and 7.4–7.9 kcal mol −1 (eq→ts) with ΔG° 0.6–0.9 kcal mol −1 . The N(2)-Me inversion barriers are 10.4–11.4 (ax→ts) and 11.6–13.1 kcal mol −1 (eq→ts) with ΔGδ 1.2–1.7 kcal mol −1 . The barrier to ring inversion is ca . 12.7 kcal mol −1 . “R value” analysis shows the ring to have a 56.5±2δ dihedral angle about the C(5)-(6) bond, indicative of the expected chair conformation.

Photochemical reduction of carbon–carbon and carbon–nitrogen double bonds by benzeneselenol

Irradiation of β-aryl-αβ-unsaturated carbonyl compounds and of some imino-derivatives of benzaldehyde in the presence of benzeneselenol leads to formation of the corresponding saturated compounds.

S H 2 reactions of diphenyl diselenide; preparation and reactions of bridgehead selenides

For the SH2 process R·+ PhSeSePh → PhSeR + PhSe·, k=ca. 5 × 107 mol–1 s–1 at 80 °C in benzene when R is primary alkyl; with 1-adamantyl radicals this SH2 displacement affords a route to 1-adamantyl phenyl selenide which, on oxidation and pyrolysis of the resultant selenoxide, gives adamantan-1-ol; in contrast the selenoxide from bicyclo[3.3.1]nonan-1-yl phenyl selenide decomposes via bicyclo[3.3.1]non-l-ene.

Conformational equilibria and nitrogen inversion in tetrahydro-1,2,5-oxadiazines

Abstract Conformational equilibria and nitrogen inversion barriers in some tetrahydro-1,2,5-oxadiazines have been investigated by 1 H NMR spectroscopy and by chemical equilibration. The conformational free energy differences obtained are: 4-methyl, 1.2±0.2; 6- p -nitrophenyl, 1.4±0.2kcal mole −1 . Barriers to inversion of the N atom at position 2 are in the region 14.1–15.6 kcal mole −1 . The conformational behaviour of the tetrahydro-1,2,5-oxadiazine ring is shown to be composed of aspects of the behaviour of the tetrahydro-1,2-and 1,3-oxazine rings.

The barrier to rotation about the N–O bond

Barriers to rotation about the N–O bond in the hydroxylamine derivatives (4) have been found to be ca. 15 kcal mol–1. There is a sizeable contribution to these barriers from non-bonded interactions in the transition states.

Electron spin resonance spectra of selenuranyl radicals R2Se–X

E.s.r. spectra assigned to the σ* selenuranyl radicals R2Se[graphic omitted]X (R = alkyl or aryl) are detected in solution during photochemical generation of X·[CF3S·, R′C(O)S·, Me3CO·, or Me3SiO·] in the presence of dialkyl or alkyl aryl selenides.

Structure and conformation of methylated hydroxylamines

Electron diffraction studies show that methylated derivatives of hydroxylamine exist in two conformations differing by a 180° rotation about the N–O bond, as predicted by M.O. calculations, but with a much smaller free energy difference than the calculations would suggest.