Pyridinethiones. XI. Diastereoselective aldol condensations with 2(1H)-pyridones, 2(1H)-pyridinethiones,and the crystal structure of 3-(1-hydroxy-2-methyl-3-oxo-3-(4-chlorophenyl)propyl-1-isoprpyl-2(1H)-pyridinethione

Aldol condensation of 3-formyl-2(1H)-pyridinethiones and the corresponding pyridones with ketones such as acetophenones in aqueous base yields 3-hydroxy-1-propanones in high yields. Reaction with propiophenone showed this reaction to be highly diastereoselective as only the erythro-isomer is formed at room temperature. This assignment was based on an X-ray crystallographic investigation of the compound given in the title. Aldol condensations of a number of related 3-acetyl-2(1H)-pyridinethiones with benzaldehyde yielded the corresponding trans-vinyl ketones.     

Unbiased Simulation of Rare Events in Continuous Time

Methodology and Computing in Applied Probability - For rare events described in terms of Markov processes, truly unbiased estimation of the rare event probability generally requires the avoidance...     

Ab initio SCF and limited CI calculations of the d-d transitions in cobalt oxide

Ab initio calculations using an extended set of gaussian-type orbitals have been performed for the CoO₆ ^10- cluster in the Hartree-Fock approximation and with a limited configuration interaction. The results have been compared with those of crystal-field theory. CoO is found to be a very ionic system with localized d-electrons. The excited d-states may be described using a simple configuration interaction scheme, which is found to be almost equivalent to a crystal-field parameterized configuration interaction built on Hartree-Fock results. Localization and delocalization phenomena in openshell systems have been discussed.     

Pyrogallol[4]arenes as artificial receptors for l-carnitine

Complexation thermodynamics of pyrogallol[4]arenes with l-carnitine and other biologically important ammonium ions were investigated by isothermal titration calorimetry.     

Formation of linear and cyclic polyoxetanes in the cationic ring‐opening polymerization of 3‐allyloxymethyl‐3‐ethyloxetane and subsequent postpolymerization modification of poly(3‐allyloxymethyl‐3‐ethyloxetane)

The synthesis of 3‐allyloxymethyl‐3‐ethyloxetane (AllylEHO) and its polymerization with BF₃ × Et₂O is described in this study. Size exclusion chromatography (SEC) and membrane osmometry are used for the determination of molecular weights of the obtained products, ranging from M_n,SEC = 41,500‐131,500 g/mol. ¹H NMR spectroscopy, SEC, as well as MALDI‐TOF MS reveal the formation of cyclic tetramer beside low, but detectable concentrations of larger cyclic oligomers as by‐products during the polymerization process. These results help to understand mechanistically why attempts for a controlled homopolymerization of AllylEHO fail and why a controlled homopolymerization of oxetanes has not been described so far in the literature. Additionally, the high versatility of allyl‐functional polyoxetane for postpolymerization modification is proven by thiol–ene reactions with 3‐mercaptopropionic acid and N‐acetyl‐L ‐cysteine methyl ester. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Automatic selection of indicators in a fully saturated regression

We consider selecting a regression model, using a variant of the general-to-specific algorithm in PcGets, when there are more variables than observations. We look at the special case where the variables are single impulse dummies, one defined for each observation. We show that this setting is unproblematic if tackled appropriately, and obtain the asymptotic distribution of the mean and variance in a location-scale model, under the null that no impulses matter. Monte Carlo simulations confirm the null distributions and suggest extensions to highly non-normal cases. An erratum to this article can be found at     

Broadband dielectric dispersion in ferroelectric P(VDF-TrFE) copolymer films

Ferroelectric polyvinylidenefluoride-trifluoroethylene copolymer films with different thicknesses are prepared by a solvent-cast technique, by spin coating, and by a horizontal Langmuir–Blodgett technique respectively. The frequency dependent dielectric permittivity of these films is investigated with varying sample thickness and varying temperature in the ferroelectric as well as in the paraelectric phase. A dielectric relaxation according to a Vogel–Tamman–Fulcher law of the relaxation times is found in all samples. However, the relaxation times extracted from the dielectric permittivity in the frequency range are not consistent with the relaxation times determined from the temperature range. An explanation for this behavior is given by a temperature dependent distribution of relaxation times. Additionally, in thin samples a second relaxation with a weak anomalous temperature dependence, i.e. an increasing relaxation time with increasing temperature, is observed at high frequencies. Detailed investigations show that this behavior can be attributed to an electrode effect.