The effect of ionic liquids on the outcome of nitrile oxide cycloadditions

Nitrile oxide cycloadditions between benzonitrile oxide and a series of alkenes were investigated in ionic liquids and molecular solvents. The regioselectivity of the process alters on changing solvent type, with the steric requirements of the reaction being increased in ionic liquids. The rate of the cycloaddition process was found to be faster in ionic liquid solvents, and a concomitant increase in the rate of dimerisation of the nitrile oxide starting material was also observed.     

Copper(II) and zinc(II) complexes with 2-formylpyridine-derived hydrazones

In the present work 2-formylpyridine-para-chloro-phenyl hydrazone (H2FopClPh) and 2-formylpyridine-para-nitro-phenyl hydrazone (H2FopNO₂Ph) were obtained, as well as their copper(II) and zinc(II) complexes [Cu(H2FopClPh)Cl₂] (1), [Cu(2FopNO₂Ph)Cl] (2), [Zn(H2FopClPh)Cl₂] (3) and [Zn(H2FopNO₂Ph)Cl₂] (4). Upon re-crystallization in DMSO:acetone conversion of 2 into [Cu(2FopNO₂Ph)Cl(DMSO)] (2a) and of 4 into [Zn(2FopNO₂Ph)Cl(DMSO)] (4a) occurred. The crystal structures of 1, 2a, 3 and 4a were determined.     

Carbonyl groups development on degraded cellulose. Correlation between spectroscopic and chemical results

Cellulose undergoing accelerated hydrothermal ageing gives a pattern of carbonyl groups whose vibrational modes were observed in UV/VI/NIR, FTIR and Raman spectra. Indirectly their presence in degraded samples was observed traced by the changes in the degree of polymerization (DP) and acidity (pH). Conjugated ketonic groups found in FTIR and Raman spectra after accelerated ageing were correlated to the chromophores detected by UV/VIS. A simple model describing the formation of chromophores was put forward and verified by experiments. PACS 81.05.-t; 82.20.Wt; 36.20.Kd; 36.20.Ng     

Hyperconjugative Control by Remote Substituents of Diastereoselectivity in the Oxygenation of Hydrocarbons

The oxidation of 2-substituted adamantanes (2) with TFDO (1) is reported. The data show a stereodifferentiation of the chemical environments induced by remote electron-withdrawing substituents which produces remarkable Z/E diastereoselectivity in the oxidation of the tertiary C(5)-H and C(7)-H bonds. The results show a bell-shaped correlation between the Z/E stereoselectivity and the substituent constant sigma(I), which is interpreted in terms of hyperconjugative stabilization of the diastereomeric transition states.     

Excimer laser-induced temperature jump-measurements on the recombination kinetics of the gas-phase FSO3 + FSO3 ⇔ F2S2O6 equilibrium between 415 and 525 K

The kinetics of the recombination reaction corresponding to the FSO₃ + FSO₃ ? F₂S₂O₆ equilibrium system has been studied. A time-resolved absorption spectroscopy technique was employed to monitor the appearance of thermally generated FSO₃ radicals at 450 nm following a small temperature jump induced after partial laser photodissociation of F₂S₂O₆ at 193 rim. The recombination rate constants have been determined over the temperature range 415–525 K and a N₂ pressure range 10–600 torr. The reaction was found to be in its first order regime. The resulting limiting high pressure rate constants were combined with previous values measured in this laboratory at lower temperatures yielding the expression ??_{rec, x} = (4.5 ± 0.2) × 10^?14 (T/300)^{(1.0 ± 0.1)} cm³ molecule^?1 s^?1 between 293 and 525 K. The temperature coefficient of ??_{rec, x} is smaller than the one derived from steady-state experiments of the thermal dissociation of F₂S₂O₆ and the equilibrium constant of the system. A recently formulated version of the canonical statistical adiabatic channel model was used to interprete the rate constants.     

Synthesis of 5-Aryl-3-(4-pyridyl)-1,2,4-oxadiazoles

The title oxadiazoles were formed in the reaction of N-(4-pyridylmethyl)arylamides with nitrosyl chloride in low yields.     

Evidence for a resonant structure of the hadron production from e+e− annihilations in the 1700–1950 cm energy region

We present experimental evidence for a resonant behaviour of the hadron production from e⁺e^? annihilations at the e⁺e^? storage ring ADONE. A Breit-Wigner fit to the enhancement present between 1800 and 1850 MeV gives the following parameters M = 1812_?13⁺⁷ MeV, Γ = 34_?15⁺²¹ MeV.