GNO Solar Neutrino Observations: Results for GNOI

We report the first GNO solar neutrino results for the measuring period GNOI, solar exposure time May 20, 1998 till January 12, 2000. In the present analysis, counting results for solar runs SR1 - SR19 were used till April 4, 2000. With counting completed for all but the last 3 runs (SR17 - SR19), the GNO I result is [65.8 +10.2 -9.6 (stat.) +3.4 -3.6 (syst.)]SNU (1sigma) or [65.8 + 10.7 -10.2 (incl. syst.)]SNU (1sigma) with errors combined. This may be compared to the result for Gallex(I-IV), which is [77.5 +7.6 -7.8 (incl. syst.)] SNU (1sigma). A combined result from both GNOI and Gallex(I-IV) together is [74.1 + 6.7 -6.8 (incl. syst.)] SNU (1sigma).Comment: submitted to Physics Letters B, June 2000. PACS: 26.65. +t ; 14.60 Pq. Corresponding author: [email protected] ; [email protected]

Ferrocenyl carbocations. The ionization of ferrocenyl alcohols in aqueous sulfuric acid

A detailed study of the ionization equilibrium between ferrocenyl alcohols and α-ferrocenyl carbocations in aqueous sulfuric acid has been performed by spectral methods. The spectral characterization of the carbocations, the extent of their formation as a function of the proton-donor ability of the solvent, and the determination of the equilibrium constants are reported. The behavior of ferrocenyl alcohols as indicators compared to that of triarylmethanols is discussed. The transmission of the polar effects of the heteroannular substituents, the heteroannular bridging of an α-hydroxytrimethylene chain, and the high charge delocalization power of the carbocation are also examined

13C NMR Study of 2,6-Di-t-butyl-4-arylpyrylium and Thiopyrylium Cations. Carbon Shifts versus Reactivities

The carbon shifts of 2,6-di-t-butyl-4-arylpyrylium and thiopyrylium cations (aryl = XC6H4- with X = p-N02 , m-Cl, p-Cl, H, p-Me, p-MeO, p-NMe2 ) have been determined in CD3CN. While the C-4 chemical shifts of the two heteroaromatic rings are largely affected by rr-polarization, as shown by the shielding induced by electron-withdrawing substituents, the C-2 (C-6) chemical shifts are free from such effect. The C-2 (C-6) and C-4 chemical shifts have been compared with the corresponding second-order rate constants for the methoxide attachment to C-2 (C-6) and C-4 positions (k2 and k4 , respectively), obtained in MeOH at 25 °C. For both the cation series the C-2 (C-6) chemical shifts are linearly correlated with the corresponding log k2 values, thus suggesting a charge control for the methoxide attachment to these cations. At variance, the C-4 chemical shifts do not show any correlation with log k4 values. Thus, whenever the chemical shifts are affected by 1t -polarization, they are no longer reliable indicators of reactivity changes, despite the dominant role of charge-charge interactions in the transition state

Stereochemical consequences of the intramolecular hydrogen bond in 1′-acetyl-1-α-hydroxyethyl- and 1,1′-bis(α-hydroxyethyl)ferrocenes

1′-Acetyl-1-α-hydroxyethyl- and 1,1′-bis(α-hydroxyethyl)ferrocenes and the carbocations derived from them have been characterized by electronic, infrared and NMR spectroscopy. The existence of intramolecular hydrogen bonds between the interannular substituents in the various species examined has been established. The restricted rotation caused by such interaction leads to preferential formation of pairs of enantiomers

Ferrocenyl carbocations. The ionization of ferrocenyl alcohols in aqueous sulfuric acid

A detailed study of the ionization equilibrium between ferrocenyl alcohols and α-ferrocenyl carbocations in aqueous sulfuric acid has been performed by spectral methods. The spectral characterization of the carbocations, the extent of their formation as a function of the proton-donor ability of the solvent, and the determination of the equilibrium constants are reported. The behavior of ferrocenyl alcohols as indicators compared to that of triarylmethanols is discussed. The transmission of the polar effects of the heteroannular substituents, the heteroannular bridging of an α-hydroxytrimethylene chain, and the high charge delocalization power of the carbocation are also examined