Selective domino ring-closing metathesis-cross-metathesis reactions between enynes and electron-deficient alkenes

[reaction: see text] A selective domino ring-closing metathesis (RCM)-cross-metathesis (CM) process between enynes and electron-deficient alkenes is reported. The conditions have been optimized for enynes 3 and methyl acrylate with catalyst IV. The scope and limitations of this reaction are described, and a possible mechanism is discussed.     

Transition between dilute and concentrated solution behaviour as revealed by excimer fluorescence

Excimer fluorescence measurements at 25° on polystyrene, with molecular weights 111,000, 392,000 and 900,000, in 1,2-dichloroethane over an extended concentration region are reported. The curve representing the normalized ratio of excimer to monomer fluorescence intensities shows an upward curvature at m>cm>[m>ηm>] ≈ 1 for all the molecular weights. This observation is attributed to enhanced intermolecular excimer formation. Some theoretical aspects on this phenomenon are also considered.     

Comparative study by single crystal X-ray structure determinations of tetramethylaminoborane and tetramethylethene at 110 K

The single crystal structures of the two isoelectronic and isosteric compounds tetramethylaminoborane and tetramethylethene have been determined by an X-ray study at 110 K. The distances of the central bonds are refined to 140.3(1) pm (B=N) and 134.8(1) pm (C=C), the CXXC-torsion angles (XX=CC, BN) are smaller than 1° in both compounds. A bond-length-bond-order correlation for the aminoboranes [(CH₃)₂N] _n B(CH₃)_{3–n} withn=1, 2, and 3 give a regression coefficient of 0.9977, the same is found for the CNC-angle as a function of the CBNC-torsion angle. Also, the comparison among these aminoboranes show that the variation of CBNC-torsion angles has more influence on bond lengths at small angles.     

Can time-homogeneous diffusions produce any distribution?

Given a centred distribution, can one find a time-homogeneous martingale diffusion starting at zero which has the given law at time 1? We answer the question affirmatively if generalized diffusions are allowed.     

Facile Activation of Zinc. Preparation of Cyclobutanones via Dichloroketene and Cyclopropanes Using the Simmons-Smith Reaction

Zinc powder activated by heating in an inert atmosphere gave good yields when used for the title reactions. The very easy work up procedure for the cyclobutanones further increases the potential of the method.     

Polypyrrole - Semiconductor photovoltaic devices

Abstract

A new approach is given for obtaining fast electro-optical response and good angular-viewing characteristics in a liquid-crystal variable-retardation device. The improved characteristics make the new device well suited for use in field-sequential color systems.     

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...     

Amperometric nitrite sensor based on free-standing carbon nanotube/methylene blue composite paper

Ionics - Free-standing paper-like electrochemical sensors have many advantages such as high flexibility, thickness adjustability, and large electroactive surface area, when compared to traditional...