Holger Hartwig

Semiempirical and ab initio study of closed and open shell derivatives of 10-methylisoalloxazine: a model of flavin redox states

Abstract The structures of a series of neutral and charged derivatives of 10-methylisoalloxazine in three different redox states have been optimized with the semiempirical PM3 method and with ab initio methods at Hartree-Fock level. The isoalloxazine ring is planar in the oxidized and one electron reduced state, except for the cations with a proton at N1, and it is folded in the two electron reduced state. Single point MP2 and self consistent reaction field calculations have been used for the analysis of the energies in the gas phase and in a polar medium. The energy difference between the cations with a proton at N1 and O2 is small for each redox state and depends on the solvent. Protonation and deprotonation energies have been calculated.

The 33S Nuclear Quadrupole Hyperfine Structure in the Rotational Spectrum of 32S, 33S Dimethyl Disulfide

Abstract We investigated the rotational spectrum of 32S, 33S dimethyl disulfide in natural abundance by molecular beam Fourier transform microwave spectroscopy. We were able to determine the complete 33S quadrupole coupling tensor, the rotational and centrifugal distortion constants and the internal rotation parameters of the two methyl tops. The rotational constants were found to be A = 8113.8847(23) MHz, B = 2800.6203(30) MHz and C = 2557.2245 (32) MHz. The results are compared with former publications.

The structure of 2,2-dimethyloxirane obtained by microwave spectroscopy: A comparison of oxiranes and thiiranes

Abstract The microwave spectra of the heavy atom isotopomers of 2,2-dimethyloxirane, (CH 3 ) 2 COCH 2 , were observed in natural abundance using a molecular beam Fourier transform-microwave spectrometer (MB-FTMW). The rotational constants were obtained and structures were derived using the r s , r 0 , and r Δ0 methods. The r s (C–C) bond length in the ring is 1.444(6) A, the r s (C–O) bond lengths are 1.437(2) and 1.419(7) A, and the C(ring)–C(methyl) distance is 1.522(3) A.

The Rotational Spectrum of 2,2-Dimethyloxirane

Abstract The microwave spectrum of 2,2-dimethyloxirane (isobutylene oxide) in the ground and torsionally excited states was assigned and analyzed. The potential barriers hindering the internal rotation described by V3 = 11.312(9) kJ/mol and V’1 2 = 1.059(32) kJ/mol and the angles between the axes of inertia and the internal rotation axes were determined.

A Contribution to the Microwave Spectra of eis- and trans-2,3-Dimethyloxirane by Fourier Transform Spectroscopy

Abstract Microwave Fourier transform spectroscopy was used to reinvestigate the rotational spectra of cisand trans-2,3-dimethyloxirane. The potential barriers hindering the internal rotation, internal rotation parameters, and partial rs-structures were determined.