Photoelectron spectra of the gauche and trans conformers of 1,2-bromochloroethane

The HeI photoelectron spectra of the gauche and trans conformers of 1,2-bromochloroethane have been obtained by analysis of time-averaged spectra recorded at different temperatures. Variations in ionization potentials of the two conformers are consistent with data obtained from molecular orbital calculations. Analysis of a HEII spectrum and comparisons with the related molecules 1,2-dichloroethane and 1,2-dibromoethane shows that the ClBr non-bonded interactions include both through-bond and through-space contributions.     

The absolute partial photoionization cross section for the production of the X 2B1 state of H2O+

The absolute partial photoionization cross section for the production of the ground state of the water molecule ion has been measured from threshold up to an equivalent photon energy of 34 eV using dipole (e,2e) spectroscopy. This data obtained from a constant ionic state scan is consistent with earlier dipole (e,2e) measurements obtained from photoelectron branching ratios and the total photoabsorption measurement. The new data which extends to lower energy is compared with two recent independent measurements obtained using tuneable synchrotron radiation. These two synchrotron radiation measurements are in disagreement with each other in the region between 18 and 22 eV where the two data sets overlap. While good agreement is obtained with the work of Truesdale et al. above 22 eV significant differences exist at lower energies. In contrast good agreement is found with the work of Dutuit et al. from threshold up to 17.5 eV and at 20 eV but not in the intervening region. The measurements are also compared with the results of a variety of earlier reported theoretical calculations.     

Preparation of isoxazolidinyl nucleoside enantiomers by lipase-catalysed kinetic resolution

An efficient biocatalytic procedure to obtain chiral N,O-nucleoside derivatives consisting of a lipase-catalysed resolution of the corresponding racemates in organic solvent has been developed. Enantioselective esterification of thymine and cytosine derivatives, (±)-9a and (±)-9b, has been investigated by comparing the efficiency of different lipases and acyl donors. Since esterification of (±)-9a and (±)-9b, occurred with low enantioselectivity (E ? 14) in the presence of the lipases considered, for preparative purposes we resorted, with success, to a double sequential kinetic resolution, using Lipozyme IM as the best catalyst. This approach enables us to obtain all the enantiomers with ee ? 95%. The absolute configuration of the new chiral N-acetyl cytosine derivative 9b was established by circular dichroism spectroscopy.