The photoelectron spectra of tricyclo[3.3.0.02,6]Octene and tricyclo[3.3.0.02,6]Octane

The photoelectron spectra of tricyclo[3.3.0.0^2,6]octene (1) and tricyclo[3.3.0.0^2,6]octane (2) have been recorded. The first bands in these spectra are correlated with orbitals which are linear combinations of the Walsh orbitals and of the olefinic π-orbital. This assignment is based on a zero differential overlap molecular orbital model as well as on the results of extended Hückel calculations. The resonance integral <π|H|W > for 1 is found to be ?1.34 eV.     

Synthesis, spectroscopic, and structural properties of spirocyclopropanated bicyclobutylidenes and their radical cations

The spirocyclopropanated bicyclobutylidenes 3-7 have been prepared by McMurry coupling of the corresponding spirocyclopropanated cyclobutanone (3 and 5), Staudinger-Pfenniger reaction (4), oxidative coupling of a Wittig ylide (4) or Wittig olefination of perspirocyclopropanated cyclobutanone (6 and 7). The structure of the parent 2a and the perspirocyclopropanated bicyclobutylidene 5 was determined by X-ray crystallography which disclosed considerable steric congestion around the double bond. As a result 5 did undergo addition of dichlorocarbene, epoxidation with meta-chloroperbenzoic acid, and cyclopropanation with CH2I2/ZnEt2, but did not add the more bulky dibromocarbene. The reaction of 5 with tetracyanoethene proceeded smoothly, but led to a formal [3+2] cycloadduct across the proximal single bond of one of the inner cyclopropane rings. The consecutive spirocyclopropanation of bicyclobutylidene led to a bathochromic shift in the UV spectra of 12 and 17nm, respectively, for each pair of beta- and alpha-spirocyclopropane groups. In the He(I)-photoelectron spectra of these bicyclobutylidenes, the effect of spirocyclopropanation upon their pi-ionization energies (pi-IE,) was found to be almost additive, leading to a lowering of 0.05 eV per any additional beta-spirocyclopropane, and 0.28-0.22 eV per additional alpha-spirocyclopropane group; this indicates an increasing nucleophilicity of the double bonds in the order 1 < 4 < 3 < 5. Following the radical cations of the three symmetrical bicyclobutylidenes without (2a, b) and with six (5) spiroannelated cyclopropane rings, the radical cations of two symmetrical bicyclobutylidenes with two (4) and four (3) such rings were studied by ESR spectroscopy. Whereas 2b.+, 3.+, and 5.+ could be generated by electrolytic oxidation of the corresponding hydrocarbons in solution, the spectra of 2a.+ and 4.+, with unsubstituted 2,2',4,4'-positions, were observed upon radiolysis of their neutral precursors in a Freon matrix. On going from 2a.+ to 4.+, the coupling constant [aH] of the eight beta protons in the 2,2',4,4'-positions of bicyclobutylidene increases from 2.62 to 3.08 mT, and that of the four gamma protons in the 3,3'-positions changes from 0.27 to 0.049 to 0.401 mT on passing from 2a.+ via 2b.+ to 3.+. Computations by means of the density functional theory (DFT) at the B3LYP/6-311+G*//B3LYP/6-31G* level reproduce well the experimental hyperfine data.     

Growth of polymer crystals during annealing

Observations by transmission electron microscopy are reported on the processes involved in polymer crystal growth during annealing. The observations suggest that crystal growth occurs by two processes. One process involves the melting of those regions of the crystals in which the melting point is lower than the annealing temperature. The polymer melt due to the melting process gradually becomes incorporated into the unmolten crystals, resulting in crystal growth. The alternative process is solid-state crystal growth by the migration of the amorphous region between crystallites.     

Experimental results on neutrino-electron scattering

A determination of sin² θ _w based on measurements of elastic scattering of muon-neutrinos and muon-anti-neutrinos on atomic electrons is described. These purely leptonic processes were studied using the CHARM calorimeter exposed to neutrino and antineutrino wide-band beams at the CERN super proton synchrotron. A total of 83±16 neutrino-electron and 112±21 antineutrino-electron events have been detected. From the measurement of the ratio of muon-neutrino and muon-antineutrino cross-sections a value of sin² θ _w =0.211±0.037 was obtained.