The michael induced ramberg-bäcklund homologation to conjugated isoprenoids

Treatment of the sulfones 1 or 2 with sodium phenylsulfinate in DMSO affords the head-to-tail coupled conjugated monoterpenoids 5–8 in comparable amounts. The corresponding reaction of 3 gives the isomers 16 and 17. The tail-to-tail homologation of 4 furnishes chiefly a 2E,4E/Z-mixture of the conjugated isoprenoids 18 and 19. The various isoprenoid mixtures are separated into their components and the configuration of the isomers is established by ¹H NMR double resonance and the NMR/NOE technique. The head-to-tail and tail-to-tail coupled isoprenoid mixtures 5–8 and 18–21, respectively, are isomerized to 2E/Z, 4E-mixtures in a 2:1 ratio. The C₁₅-sulfones 11 and 13 are obtained by treatment of 1 with the head-functionalized isoprene synthon 10. Some speculations on the stereochemical course of the MIRB-homologation are presented.     

Single atom adhesion in optimized gold nanojunctions

We study the interaction between single apex atoms in a metallic contact, using the break junction geometry. By carefully training our samples, we create stable junctions in which no further atomic reorganization takes place. This allows us to study the relation between the so-called jump out of contact (from contact to tunneling regime) and jump to contact (from tunneling to contact regime) in detail. Our data can be fully understood within a relatively simple elastic model, where the elasticity k of the electrodes is the only free parameter. We find 5相似文献   

The molecular structure of trifluoroethene in the gas-phase as determined from electron diffraction and microwave data

The molecular structure of trifluoroethene was determined from electron diffraction data and the microwave rotational constants of the parent and deuterated molecule, corrected for zero-point vibrational motion. A GVFF adjusted to fit the vibrational frequencies was used for the correction. The molecule was found to be planar. Assuming equal geminal C1—F bond lengths, the following r_g distances and r_av angles are found: C1—F = 1.316 ± 0.011 Å, C2—F = 1.342 ± 0.024 Å, CC = 1.341 ± 0.012 Å, C—H = 1.100 ± 0.02 Å, ∠C—C—F1 = 123.1 ± 1.5°. ∠C—C—F2 = 124.0 ± 0.6°, ∠C—C—F3 = 120 ± 0.7° (Fl trans to F3) and ∠C—C—H = 124.0 ± 1.7°.The error limits include 3σ (σ = estimated standard deviation) and estimates of the systematic errors. The analysis suggests that all the C1—F distances are not equivalent, neither are the C2—C1—F angles, though the differences are not significant (10% level).     

On real algebraic vector bundles

Supported by the Netherlands Organisation for Scientific Research (NWO)