Search results for "Reaction"

A Photochemical One-Pot Three-Component Synthesis of Tetrasubstituted Imidazoles

2014

Tetrasubstituted imidazoles can be formed in a photochemical one-pot synthesis from aldehydes, α-aminonitriles, and isoxazoles. Condensation of the first two components produces α-(alkylideneamino)nitriles which react under basic conditions with the acylazirines formed in situ by photochemical ring transformation of the isoxazole component. This process includes an unusual cleavage of the C(2)-C(3) bond of the acylazirine. The reaction mechanism was studied by DFT calculations.

Über die photosensibilisierte autoxydation von polyvinylalkohol

1968

Polyvinylalkohol wurde in wasriger Losung bei 30°C unter Belichtung mit einer Quecksilberhochdrucklampe einer mit benzophenn-3.3′-disulfonsaurem Natrium photosensibilisierten Autoxydation unterworfen. Als Reaktionsprodukte wurden Wasserstoffperoxid, Sauren und Kohlendioxid ermittelt. Unter den gewahlten Reaktionsbedingungen werden die Makromolekule statistisch abgebaut. Viskositatsmessungen und analytische Bestimmungen zeigen, das pro Spaltung der polymerkette nur eine Carboxylendgruppe entsteht. Ein Reaktionsmechanismus wird diskutiert. Polyvinylalcohol was oxidized in water solution at 30°C by irradiation with a mercury high pressure lamp and benzophenon-3.3′-disodiumdisulfonate as sensit…

Reaction Mechanism of an Intramolecular Oxime Transfer Reaction: A Computational Study

2014

Density functional theory (PBE0/def2-TZVPP) calculations in conjunction with a polarizable continuum model were used to assess the mechanism of the intramolecular oxime transfer reaction that leads to the formation of isoxazolines. Different diastereomers of the intermediates as well as different oximes (formaldehyde and acetone oxime) were considered. The computed reaction profile predicts the water-addition and -expulsion steps as the highest barriers along the pathway, a conclusion that is in line with the experimental evidence obtained previously for these reactions.

DFT Theoretical Study on the Reaction Mechanism of the Nitrate Radical with Alkenes:  2-Butene, Isobutene, 2-Methyl-2-butene, and 2,3-Dimethyl-2-bute…

2000

A general mechanism for the reactions of the NO3 radical with 2-butene, isobutene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene is proposed on the basis of density functional theory (DFT) calculati...

Density Functional Theory Study of the Cycloaddition Reaction of Furan Derivatives with Masked o-Benzoquinones. Does the Furan Act as a Dienophile in…

2002

The molecular mechanism for the cycloaddition reaction between 2-methylfuran and a masked o-benzoquinone has been characterized using quantum mechanical calculations at the B3LYP/6-31G theory level. An analysis of the results on the reaction pathway shows that the reaction takes place along a polar stepwise mechanism. The first and rate-determining step corresponds to the nucleophilic attack of the furan ring on the doubly conjugated position of the 2,4-dienone system present at the masked o-benzoquinone to give a zwitterionic intermediate. Closure of this intermediate affords the formally [2 + 4] cycloadduct. For the second step two reactive channels have been characterized corresponding t…

Competing Ring-Photoisomerization Pathways in the 1,2,4-Oxadiazole Series. An Unprecedented Ring-Degenerate Photoisomerization

2002

The irradiation of some 5-alkyl-3-amino-1,2,4-oxadiazoles at lambda = 254 nm in methanol in the presence of triethylamine (TEA) gave ring-photoisomerization both into 2-alkyl-5-amino-1,3,4-oxadiazoles and, unprecedently, into the ring-degenerate 3-alkyl-5-amino-1,2,4-oxadiazoles. The competing ring contraction-ring expansion route and the internal cyclization-isomerization mechanism explain the results.

1984

A dimeric biradical •M plays a central role in the initiation of the spontancous polymerization of methyl methacrylate (M1). Besides the initiation step by chain transfer reaction, a change of the multiplicity of ˙M seems to be of importance. Evidence is given by heavy atoms in the solvent or in an inert gas atmosphere, leading to an acceleration of the overall polymerization rate. The observed effect is related to the atomic number of the respective heavy atom. Measurements of the temperature dependence of the effect for carbon tetrachloride show that — as expected — no activation energy is needed for this reaction step. The results are summarized in a reaction scheme for the initiation me…

Palladium-Catalyzed Suzuki Carbonylative Reaction of α-Halomethyl Oxime Ethers: A Regioselective Route to Unsymmetrical 1,3-Oxyiminoketones

2014

Unveiling the Substituent Effects in the Stereochemistry of [3+2] Cycloaddition Reactions of Aryl‐ and Alkyldiazomethylphosphonates with Norbornadien…

2021

1990

The effect of lithium tert-butoxide (t-BuOLi) on rate constants and equilibrium constants of reactions involved in the initial stage of the anionic polymerization of methyl methacrylate (MMA) in tetrahydrofuran, initiated by methyl α-lithioisobutyrate (P) was investigated at 23 ± 3°C. Addition of t-BuOLi decreases the rate constants of initiation and propagation by one order of magnitude; the rate constants of termination by cyclization decrease by two orders of magnitude. This leads to an overall tenfold higher preference of propagation with respect to termination and explains the favourable effect of alkoxide in the polymerization reported earlier. Within experimental error, the equilibri…