X-ray constrained unrestricted Hartree-Fock and Douglas-Kroll-Hess wavefunctions.

The extension of the X-ray constrained (XC) wavefunction approach to open-shell systems using the unrestricted Hartree-Fock formalism is reported. The XC method is also extended to include relativistic effects using the scalar second-order Douglas-Kroll-Hess approach. The relativistic effects on the charge and spin density on two model compounds containing the copper and iron atom are reported. The size of the relativistic effects is investigated in real and reciprocal space; in addition, picture-change effects are investigated and discussed for the isolated Cu atom. It is found that the relativistic terms lead to changes in the densities that are much smaller than those from the X-ray constraint. Nevertheless, the use of the relativistic corrections in the ab initio model always leads to an improvement in the agreement statistics. An interesting result of the unrestricted XC technique is the possibility of obtaining experimentally derived spin densities from X-ray data.

A novel synthetic approach to C-glycosyl-D- and L-alanines.

C-Glycosyl-(S)- and (R)-alanines 12a and 12b were synthesized from the known beta-C-glycoside 1. The nitrogen function was introduced by aza-Claisen rearrangement of the allylic thiocyanate 7, derived from the corresponding alcohol 6. The absolute configuration of the newly created chiral carbon center (C-3) was assigned by X-ray diffraction analysis of the intermediate 3(S)-isothiocyanato-D-glycero-D-galacto-decose 8a.

5-[(9H-Fluoren-9-yl-idene)meth-yl]furan-2-carbonitrile.

The title compound, C(19)H(11)NO, is stabilized by one intra-molecular C-H⋯O hydrogen bond. The compound can be synthesized in good yield (49%), by transformation of functional groups [starting with 5-(fluoren-9-ylidenemeth-yl)furan-2-carbaldehyde]. The flourene and furan ring systems are nearly coplanar, with a dihedral angle of 6.36 (7)°.

2-(9H-Fluoren-9-ylidenemeth-yl)thio-phene.

The title compound, C(18)H(12)S, contains a thio-phene ring which is disordered by rotation of 180° about the linking C-C bond. The site occupancies of the major and minor components of the disordered ring are 0.900 (3) and 0.100 (3), respectively. In one of these disordered components, the mol-ecule is stabilized by an intra-molecular C-H⋯S hydrogen bond. The compound was synthesized in good yield (80%) by a modified phase-transfer-catalysed condensation of fluorene with thio-phene-2-carbaldehyde.