Acyclic stereoselection. 21. Synthesis of an ionophore synthon having four asymmetric carbons by sequential aldol addition,claisen rearrangement and hydroboration

Allylic alcohol 7, obtained by a synthesis involving stereoselective aldol addition to an unsaturated aldehyde, is transformed by the Ireland variant of the Claisen rearrangement into unsaturated acid 9. Subsequent elaboration of this material gives homoallylic alcohols 13 and 14, which are hydroborated to obtain primarily 3 and 4. It is shown that the hydroboration is intermolecular, rather than intramolecular.     

Kinetics of pyrolysis of some biomasses widely available in Brazil

Journal of Thermal Analysis and Calorimetry - Biomass conversion via thermal processes to generate energy will be an important part of the future energy landscape. The objective of this study was...     

Ultrasonic Irradiation in Enantioselective Hydrogenation of 1-Phenyl-1,2-Propanedione

In the presence of ultrasound both the initial hydrogenation rate of 1-phenyl-1,2- propanedione and the enantiomeric excess of the main product, i.e. (R)-1-hydroxy- 1-phenylpropanone, increased by 75 % and 52 % in toluene, respectively, as compared to the silent hydrogenation.     

Average homogeneity and dimensions of measures

We introduce the concept of average homogeneity of a measure by comparing the measure to the uniform distribution in a relatively simple way. This leads to a very general notion which may be regarded as an inverse of porosity. In this paper the emphasis is given to relations between homogeneity and dimensions of measures. First we consider the effect of homogeneity on dimensions by proving an upper bound to the Hausdorff dimension as a function of homogeneity and its order. The opposite question of how dimensions effect homogeneity is solved by giving an upper bound to homogeneity in terms of upper packing dimension. We also illustrate by examples that all our results are the best possible ones.Mathematics Subject Classification (2000): 28A75, 28A80MJ acknowledges the support of the Academy of Finland, project #48557.     

Complete 1H, 13C{1H}, and 31P NMR spectral parameters of some pyrophosphates

The ¹H, ¹³C{¹H}, and ³¹P NMR spectral parameters of some pyrophosphates were determined in CDCl₃. The most complicated ¹H spectrum can be solved fully only as (A₃MN)R₆XX′R₆′(MNA₃)′, where R₆ (= ―N(CH₃)₂) is coupled only to phosphorus (X). Second‐order coupling between phosphorus was found and solved with iterative analysis. A signal shape of one of the carbon resonance cannot be explained only with couplings. Explanation for exceptional shape was searched from molecular modeling results. Copyright © 2017 John Wiley & Sons, Ltd.     

INTERACTIONS BETWEEN CATIONIC STARCH AND ANIONIC SURFACTANTS III RHEOLOGY AND STRUCTURE OF THE COMPLEX PHASE

This paper reports on studies of the rheological properties of cationic starch (CS)/ surfactant systems. The degree of substitution of the CS was 0.1 - 0.8. Surfactants investigated were sodium dodecyl sulfate (SDS), potassium octanoate (KOct), sodium decanoate (NaDe)potassium dodecanoate (KDod), sodium oleate (NaOl) and sodium erucate (NaEr). Aggregation of surfactant micelles with the polymer produces a hydrophobic and pseudoplastic gel-like complex phase with low water content and high viscosity. The rheological behavior of the gels is described by the Herschel-Bulkley model. In dilute aqueous solution the CS/surfactant aggregate structure resembles a randomly coiled polymer network, in which polymer molecules are linked by micelles. The rheological data for the gel are compatible with the assumption that the surfactants form liquid crystalline structures with the polymer anchored to the surfactant aggregates, as recently suggested for analogous systems. However, this conjecture needs to be corroborated by more direct determinations of the structure.     

Eye‐safe UV stand‐off Raman spectroscopy for the ranged detection of explosives in the field

Increasing worldwide terrorist attacks involving explosives presents a growing need for a rapid and ranged explosive detection method that can safely be deployed in the field. Stand‐off Raman spectroscopy shows great promise; however, the radiant exposures of lasers required for adequate signal generation are often much greater than what is safe for the eye or the skin, restricting use of the technique to unpopulated areas. Here, by determining the safe exposure levels for lasers typically used in Raman spectroscopy, optimal parameter values are identified, which produce the largest possible detection range using power densities that do not exceed the eye‐safe limit. It is shown that safe ultraviolet pulse energies can be more than three orders of magnitude greater than equivalent safe visible pulse energies. Coupling this to the 16‐fold increase in Raman signal obtained in the ultraviolet at 266 nm over that at 532 nm results in a 131 times larger detection range for the eye‐safe 266‐nm system over an equivalent eye‐safe 532‐nm laser system. For the Raman system described here, this translates to a maximum range of 42 m for detecting Teflon with a 266‐nm laser emitting a 100‐mm diameter beam of 23.5‐mJ nanosecond pulses. Copyright © 2015 John Wiley & Sons, Ltd.     

Activation of hafnocene catalyzed polymerization of 1-hexene with MAO and borate

A study of 1-hexene polymerization with ethylene-bis(9-fluorenyl) hafnium dichloride has been carried out using two different cocatalyst systems, methyl-aluminoxane/trimethylaluminum (MAO/TMA) and tris-isobutyl-aluminum/N,N-dimethylanilinium tetrakis(pentafluorophenyl) borate (TIBA/borate). When MAO/TMA was used, 1-hexene polymerized into a low molar mass poly(1-hexene) with low catalytic activity. Activation with TIBA/borate increased polymerization activity drastically as well as the molar mass of the polymers. In order to analyze differences in the activity profiles, UV-Vis spectroscopy was employed to investigate ligand to metal charge transitions (LMCT) of the hafnocene dichloride during the activation process. The low catalytic activity and the fast chain transfer to the cocatalyst with MAO/TMA may originate from strong bonding between the metallocene cation and the MAO/TMA species thus obstructing monomer coordination and insertion.     

Large deviations for functionals of stationary processes

Summary Let (S _n ) be a sequence ofR ^d -valued random variables adapted to the internal history of a stationary sequence of random elements (X _n ). We formulate conditions under which the principle of large deviations holds true for the sequence (S _n ).     

Total synthesis of amaminol A: establishment of the absolute stereochemistry

The first synthetic route to amaminol A with use of an organocatalytic intramolecular Diels-Alder reaction is reported. The absolute stereochemistry is proven with a crystallographic image of a cyclic carbamate of amaminol A.