Cyclobutane-bicyclobutane system. 16. Effective molarities and ionic chain mechanism in the reaction of a bifunctional nucleophile with substituted bicyclobutane

1990 ◽  
Vol 55 (7) ◽  
pp. 2090-2094
Author(s):  
Uri Haboosha ◽  
Shmaryahu Hoz
Keyword(s):  
Chain Mechanism ◽  
Bifunctional Nucleophile

Catalytic, Enantioselective Syn-Diamination of Alkenes

2019 ◽  
Author(s):  
Zhonglin Tao ◽  
Brad Gilbert ◽  
Scott Denmark
Keyword(s):  
General Solution ◽  
Organic Synthesis ◽  
Medicinal Chemistry ◽  
Catalytic Cycle ◽  
Bifunctional Nucleophile

The enantioselective, vicinal diamination of alkenes represents one of the stereocontrolled additions that remains an outstanding challenge in organic synthesis. A general solution to this problem would enable the efficient and selective preparation of widely useful, enantioenriched diamines for applications in medicinal chemistry and catalysis. In this Article we describe the first enantioselective, <i>syn-</i>diamination of simple alkenes mediated by a chiral, enantioenriched organoselenium catalyst together with a <i>N,N’-</i>bistosyl urea as the bifunctional nucleophile and <i>N-</i>fluorocollidinium tetrafluoroborate as the stoichiometric oxidant. Diaryl, aryl-alkyl, and alkyl-alkyl olefins bearing a variety of substituents are all diaminated in consistently high enantioselectivities selectivities but variable yields. The reaction likely proceeds through a Se(II)/Se(IV) redox catalytic cycle reminiscent of the <i>syn-</i>dichlorination reported previously. Furthermore, the <i>syn</i>-stereospecificity of the transformation shows promise for highly enantioselective diaminations of alkenes with no strong steric or electronic bias.

Multi-chain action of exo-D-galacturonanase from carrot

1983 ◽  
Vol 48 (12) ◽  
pp. 3579-3588
Author(s):  
Kveta Heinrichová ◽  
Jana Perečková
Keyword(s):  
Optimal Condition ◽  
Degradation Products ◽  
Degradation Kinetics ◽  
Hydrolytic Cleavage ◽  
Chain Mechanism ◽  
Modes Of Action ◽  
Enzyme Degradation ◽  
Good Agreement

Two possible modes of action of exo-D-galacturonanase from carrot (E.C. 3.2.1.67) were investigated; this enzyme catalyses the sequential hydrolytic cleavage of pectants and oligogalacturonans by a terminal action from the nonreducing end of the molecule. The experiments indicate that the investigated exo-D-galacturonanase degrades these substrates by a predominantly multi-chain mechanism. Distribution of degradation products of oligomeric substrates (hexa- and pentagalacturonide) under an optimal condition for the action of the enzyme (pH and temperature) indicates that a multi-chain enzyme attack with a prevalent simple collision is involved. Results of the enzyme degradation kinetics are in a good agreement with the above-mentioned presumption.

Isotopic exchanges in the treatment of cyclobutane with tritiated or deuterated trifluoromethanesulfonic acid or with tritiated sulfuric acid

1980 ◽  
Vol 58 (1) ◽  
pp. 1-5 ◽  
Author(s):  
Choi Chuck Lee ◽  
Eric C. F. Ko
Keyword(s):  
Mass Spectrometry ◽  
Sulfuric Acid ◽  
Trifluoromethanesulfonic Acid ◽  
Isotopic Dilution ◽  
Chain Mechanism

When cyclobutane (1) is shaken at 0 °C with [3H]CF3SO3H (2-t) or with (2H)CF3SO3H (2-d), incorporation of T or D into the hydrocarbon layer readily occurred. All eight H atoms of 1 can be involved in the exchange since polydeuterated species including octadeuterated hydrocarbons were observed by mass spectrometry. In an experiment with 1 and 2-t, quenching of the acid layer with H2O gave a mixture of cyclobutanol, cyclopropylcarbinol, and allylcarbinol in the ratio of 61:37:2, respectively, as estimated by isotopic dilution, while vpc analysis of the hydrocarbon layer showed the presence of 1, methylcyclopropane, and 1-butene in the ratio of 66:30:4. The results are explained by a carbocationic chain mechanism, involving the formation of equilibrating bicyclobutonium ions. Similar but slower incorporation of T into the hydrocarbon layer was observed when 1 was treated with [3H]H2SO4.

Design, Analysis and Fabrication of a Six-Legged Walking Machine

2005 ◽  
Author(s):  
Rakesh Sehgal ◽  
Ashutosh Tiwari ◽  
Vivek Sood
Keyword(s):  
Angular Velocity ◽  
Design Analysis ◽  
Chain Mechanism ◽  
Walking Machine ◽  
Acceleration Analysis

This paper presents the steps involved in the design, analysis and fabrication of a six-legged walking machine. The suggested machine uses the basic four bar chain mechanism and slotted lever type quick return mechanism with some modifications. The synthesis of the link lengths is based on Freudenstein’s (algebraic) three accuracy points. The velocity and acceleration analysis of oscillating links explains the effect of change in the crank’s angular velocity and acceleration on all other links. The suggested machine is capable of moving forward and backward, turning right and left and rotating around a point on the commands given.

Chain mechanism of the reactions of N,N′-diphenyl-1,4-benzoquinone diimine with thiophenol and 1-decanethiol

2012 ◽  
Vol 53 (5) ◽  
pp. 525-530 ◽  
Author(s):  
A. V. Gadomska ◽  
S. Ya. Gadomsky ◽  
V. T. Varlamov
Keyword(s):  
Chain Mechanism

THE KINETICS OF THE OXIDATION OF GASEOUS ACETALDEHYDE

1932 ◽  
Vol 7 (2) ◽  
pp. 149-161 ◽  
Author(s):  
W. H. Hatcher ◽  
E. W. R. Steacie ◽  
Frances Howland
Keyword(s):  
Carbon Dioxide ◽  
Formic Acid ◽  
Induction Period ◽  
Reaction Vessel ◽  
Oxidation Products ◽  
Main Reaction ◽  
Chain Mechanism ◽  
Subsequent Reaction ◽  
A Chain ◽  
Kinetics Of

The kinetics of the oxidation of gaseous acetaldehyde have been investigated from 60° to 120 °C. by observing the rate of pressure decrease in a system at constant volume. A considerable induction period exists, during which the main products of the reaction are carbon dioxide, water, and formic acid. The main reaction in the subsequent stages involves the formation of peroxides and their oxidation products. The heat of activation of the reaction is 8700 calories per gram molecule. The indications are that the reactions occurring during the induction period are heterogeneous. The subsequent reaction occurs by a chain mechanism. The chains are initiated at the walls of the reaction vessel, and are also largely broken at the walls.

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