Towards novel difluorinated sugar mimetics; syntheses and conformational analyses of highly-functionalised difluorinated cyclooctenones

Highly-functionalised difluorinated cyclooctenones were synthesised from trifluoroethanol using either metallated difluoroenol acetal or carbamate chemistry, followed by a [2,3]-Wittig rearrangement or aldol reaction. Efficient RCM reactions afforded the title compounds which showed rather restricted fluxional behaviour by VT (19)F NMR. Topological characterisation by molecular modelling and NOESY/ROESY experiments offered a number of challenges, but allowed the identification of two favoured boat-chair conformers which interconverted by pseudorotation with relatively large activation barriers.     

XeAuF

XeAuF has been detected and characterized using microwave rotational spectroscopy. It was prepared by laser ablation of Au in the presence of Xe and SF(6), and stabilized in a supersonic jet of Ar. The spectrum was measured with a cavity pulsed jet Fourier transform microwave spectrometer, in the frequency range 6-26 GHz. Rotational constants, centrifugal distortion constants, and (131)Xe and (197)Au nuclear quadrupole coupling constants have been evaluated. The molecule is linear, with a short XeAu bond (2.54 A), and is rigid. The (131)Xe nuclear quadrupole coupling constant (NQCC) is large (-135 MHz). The (197)Au NQCC differs radically from that of uncomplexed AuF. The results are supported by those of ab initio calculations which have given an XeAu dissociation energy approximately 100 kJ mol(-1), plus Mulliken and natural bond orbital populations, MOLDEN plots of valence orbitals, and an energy density distribution. All evidence is consistent with XeAu covalent bonding in XeAuF.     

The microwave spectrum of bromine isocyanate,Brnco: Determination of rotational constants from quadrupole hyperfine structure

A novel method has been developed to evaluate accurate rotational constants from the microwave spectrum of the unstable molecule bromine isocyanate, using perturbations in nuclear quadrupole hyperfine structure. It has been applied to this prolate near-symmetric rotor to determine A_v and x_ab accurately, entirely from a-type R branches. The method has been made possible by the development of a special computer program for global léast-squares fitting to rotational and centrifugal distortion constants, along with all components of the Br nuclear quadrupole coupling tensor.     

Microwave spectra and structures of KrAuF, KrAgF, and KrAgBr; 83Kr nuclear quadrupole coupling and the nature of noble gas-noble metal halide bonding

Microwave spectra of the complexes KrAuF and KrAgBr have been measured for the first time using a cavity pulsed jet Fourier transform microwave spectrometer. The samples were prepared by laser ablation of the metal from its solid and allowing the resulting plasma to react with an appropriate precursor (Kr, plus SF6 or Br2) contained in the backing gas of the jet (usually Ar). Rotational constants; geometries; centrifugal distortion constants; vibration frequencies; and 197Au, 79Br, and 81Br nuclear quadrupole coupling constants have all been evaluated. The complexes are unusually rigid and have short Kr-Au and Kr-Ag bonds. The 197Au nuclear quadrupole coupling constant differs radically from its value in an AuF monomer. In addition 83Kr hyperfine structure has been measured for KrAuF and the previously reported complex KrAgF. The geometry of the latter has been reevaluated. Large values for the 83Kr nuclear quadrupole coupling constants have been found for both complexes. Both the 197Au and 83Kr hyperfine constants indicate a large reorganization of the electron distribution on complex formation. A thorough assessment of the nature of the noble gas-noble metal bonding in these and related complexes (NgMX; Ng is a noble gas, M is a noble metal, and X is a halogen) has been carried out. The bond lengths are compared with sums of standard atomic and ionic radii. Ab initio calculations have produced dissociation energies along with Mulliken populations and other data on the electron distributions in the complexes. The origins of the rigidity, dissociation energies, and nuclear quadrupole coupling constants are considered. It is concluded that there is strong evidence for weak noble gas-noble metal chemical bonding in the complexes.     

Proposal for generating Fock states in traveling wave fields

We describe a proposal for the generation of a single-mode photonic number state, |N〉$|N〉$, in a traveling wave optical field. The state is obtained by state reduction from an input coherent state using Kerr media. Our method is based on a previous scheme used for hole burning in the Fock space by minimizing the Mandel Q parameter. The same method was used by Maia et al., but ours is different, it requires only one single photon injected in the entire setup and one photon detection at the end.     

Microwave spectra, geometries, and hyperfine constants of OCAgX (X = F, Cl, Br)

A pulsed jet cavity Fourier transform microwave spectrometer has been used to measure the rotational spectra of OCAgX (X = F, Cl, Br) in the frequency range 5-22 GHz. Metal atoms were generated via laser ablation and were allowed to react with CO and a halide precursor, prior to stabilization of the products within a supersonic jet of argon. These are the first experimental observations of OCAgF and OCAgBr, and the first high resolution spectroscopic study of OCAgCl. All three molecules are linear. Accurately determined rotational constants have been used to evaluate the various internuclear distances, which are found to be consistent with trends established for OCAuX and OCCuX species. The C-O distances are short, and the M-C distances are significantly longer than those in other molecules containing a metal-carbonyl bond. Precise values of centrifugal distortion constants and halogen nuclear quadrupole coupling constants have also been determined. The coupling constants are compared with the results of previous studies of OCCuX and OCAuX and are used to infer trends in the electron distributions of the molecules. Ab initio calculations have been performed and employed to predict the geometries, vibrational frequencies, and Mulliken valence orbital populations of the various species.     

The microwave spectrum, structure, chlorine nuclear quadrupole coupling constants, dipole moment, and centrifugal distortion constants of dichlorosilane

The microwave spectra of three isotopic species of dichlorosilane, SiH₂Cl₂, in its ground vibrational state, have been measured in the frequency region 8–40 GHz. The spectra have yielded values for the rotational constants, centrifugal distortion constants, and chlorine nuclear quadrupole coupling constants, as well as the molecular dipole moment, 1.13 ± 0.02 D. The molecule has C_2v symmetry, and the bond lengths and angles r(Si---Cl=2.033±Å, r(Si---H)=1.480±0.015Å, (Cl---Si---Cl)=109°43′±20±, (H---Si---H)=111°18′±40′ The centrifugal distortion constants have been compared with those calculated using a published force field.