Marshall W. Logue

d-ribofuranosyl azides. A direct conversion of 1-O-acyl-2,3-O-isopropylidene-d-ribofuranose into d-ribofuranosyl azides

Abstract Reactions of azidotrimethylsilane with 1-O-acetyl-2,3,5-tri-O-benzoyl-β- d -ribofuranose (2), and the 1,5-di-O-p-nitrobenzoyl and 1,5-di-O-acetyl derivatives, 4 and 5 respectively, of 2,3-O-isopropylidene-β- d -ribofuranose, in the presence of the Lewis acids aluminum chloride, titanium tetrachloride, or boron trifluoride etherate were studied. All three Lewis acids readily catalyze the quantitative conversion of 2 into its β- d -ribofuranosyl azide, whereas only aluminum chloride is a suitable catalyst for conversion of 4 and 5 into their azides; boron trifluoride etherate is ineffective, and titanium tetrachloride causes partial decomposition. Contrary to the behavior of 2, which gives only the β azide, 4 and 5 give, in excellent yield, anomeric mixtures of azides in which the β azide preponderates. Although dichloromethane and acetonitrile are appropriate solvents for the reaction of 2, only acetonitrile is suitable for 4 and 5, as use of the former results in the co-production of related d -ribofuranosyl chlorides.

Analysis of the temperature dependence of the racemization of Eu(III) complexes through measurement of steady-state circularly polarized luminescence

Abstract The temperature dependence of the steady-state luminescence dissymmetry ratio, g lum , has been measured for racemic Eu(III) complexes containing the terdentate ligands dipicolinate and phenylethynyl-dipicolinate. As the temperature is increased, the magnitude of the dissymmetry ratio for these species decreases due to racemization occurring during the excited state lifetime. The temperature dependence of g lum is analyzed by a non-linear curve-fitting technique to determine the activation energies for the interconversion of the enantiomers. Comparison is made with previous measurements involving time-resolved circularly polarized luminescence.

Measurement and analysis of the temperature and pressure dependence of the 7F0→5D0 excitation spectra of Eu(III) complexes with 4-phenylethynyl-2,6-pyridine-dicarboxylic acid

Abstract The pressure and temperature dependence of the 5D0→7F0 transition of Eu(III) in complexes with 4-phenylethynyl-2,6-pyridinedicarboxylic acid has been measured at various metal to ligand ratios. The spectra have been fit to a sum of Lorentzian peaks, and the temperature dependence used to determine ΔH for the equilibrium reaction for formation of the tris complex from the bis complex. The pressure dependence of the 5D0→7F0 transitions corresponding to the bis and tris species is analyzed in order to determine the associated difference in volume, ΔV, between reactants and products.

tert-Butyl 2-benzoyl-2-methyl­propanoate

The title compound, C15H20O3, is bent with a dihedral angle of 67.28 (9)° between the mean planes of the phenyl ring and a group encompassing the ester functionality (O=C—O—C). In the crystal, molecules related by inversion symmetry are connected by weak C—H⋯O interactions into infinite chains. On one side of the molecule there are two adjacent interactions between neighbouring molecules involving the H atoms of methyl groups from the dimethyl groups and the O atoms of the ketone; on the other side, there are also two interactions to another adjacent molecule involving the H atoms on the phenyl rings and the carbonyl O atoms of the ester functionality.

tert-Butyl 2-methyl-2-(4-nitro­benzo­yl)propanoate

The title compound, C15H19NO5, is bent with a dihedral angle of 61.8 (2)° between the mean planes of the benzene ring and a group encompassing the ester functionality (O=C—O—C). The dihedral angle of 0.8 (2)° between the mean planes of the nitro group and the benzene ring indicates near coplanarity. In the crystal, each molecule is linked to four adjacent molecules by weak C—H⋯O hydrogen-bonding interactions. Both benzene H atoms ortho to the ketone O atom form C—H⋯O hydrogen bonds with the keto O atoms of two neighboring molecules (of the keto and ester groups, respectively), and the two other interactions involve the H atoms from a methyl group of the dimethyl residue, displaying C—H⋯O interactions with the O atoms of the nitro groups. These four interactions for each molecule lead to the formation of two-dimensional sheets with a hydrophilic interior, held together by weak hydrogen-bonded interactions, and a hydrophobic exterior composed of protruding methyl groups which interstack with the methyl groups in adjacent sheets.

tert-Butyl 2-(4-chloro-benzo-yl)-2-methyl-propanoate.

The title compound, C15H19ClO3, is bent with a dihedral angle of 72.02 (9)° between the mean planes of the benzene ring and a group encompassing the ester functionality (O=C—O—C). In the crystal, molecules related by inversion symmetry are connected by weak C—H⋯O interactions into infinite chains. These interactions involve H atoms from a methyl group of the dimethyl residue and the O atoms of the ketone on one side of a molecule; on the other side there are interactions between H atoms of the benzene ring and the carbonyl O atoms of the ester functionality. There are no directional interactions between the chains.