Substituent

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Changle Chen - One of the best experts on this subject based on the ideXlab platform.

  • position makes the difference electronic effects in nickel catalyzed ethylene polymerizations and copolymerizations
    Inorganic Chemistry, 2018
    Co-Authors: Tao Liang, Changle Chen
    Abstract:

    A series of phosphine-sulfonate ligands and the corresponding nickel complexes are prepared and characterized. These ligands are specifically designed to bear systematically varied electron-donating and -withdrawing Substituents (H, OMe, NMe2, CF3, and Me). More importantly, these Substituents are installed at different positions on the ligand framework, namely, the para-position of the phenylphosphino group (position X), and para to the arylsulfonate group of the main ligand (position Y). These nickel complexes are highly active single-component catalysts for the polymerization of ethylene. An electron-donating Substituent at position X or an electron-withdrawing Substituent at position Y is beneficial to the properties of these nickel catalysts. Specifically, the catalyst bearing the NMe2 Substituent at position X exhibits high stability and high activity (3.3 × 106 g mol–1 h–1), and catalyzes the formation of polyethylene of high molecular weight (Mn 405 000) and high melting point (Tm 138.5 °C). This ...

  • Position Makes the Difference: Electronic Effects in Nickel-Catalyzed Ethylene Polymerizations and Copolymerizations
    2018
    Co-Authors: Tao Liang, Changle Chen
    Abstract:

    A series of phosphine-sulfonate ligands and the corresponding nickel complexes are prepared and characterized. These ligands are specifically designed to bear systematically varied electron-donating and -withdrawing Substituents (H, OMe, NMe2, CF3, and Me). More importantly, these Substituents are installed at different positions on the ligand framework, namely, the para-position of the phenylphosphino group (position X), and para to the arylsulfonate group of the main ligand (position Y). These nickel complexes are highly active single-component catalysts for the polymerization of ethylene. An electron-donating Substituent at position X or an electron-withdrawing Substituent at position Y is beneficial to the properties of these nickel catalysts. Specifically, the catalyst bearing the NMe2 Substituent at position X exhibits high stability and high activity (3.3 × 106 g mol–1 h–1), and catalyzes the formation of polyethylene of high molecular weight (Mn 405 000) and high melting point (Tm 138.5 °C). This catalyst also mediates the efficient copolymerizations of ethylene with methyl 10-undecenoate, 6-chloro-1-hexene, and trimethoxyvinylsilane

Miquel Torrentsucarrat - One of the best experts on this subject based on the ideXlab platform.

  • effects of the Substituents on the reactivity of carbonyl oxides a theoretical study on the reaction of substituted carbonyl oxides with water
    Physical Chemistry Chemical Physics, 2011
    Co-Authors: Josep M Anglada, J W Gonzalez, Miquel Torrentsucarrat
    Abstract:

    The reactions between fifteen carbonyl oxides and water have been investigated with the aim of contributing to a better understanding of the effects of the Substituents in the reactivity of carbonyl oxides. We have employed density functional theory and large scale ab initio methods (CCSD(T), CASSCF, and CASPT2), combined with transition state theory, to investigate the addition of water to carbonyl oxide and, for those carbonyl oxides having a methyl Substituent in syn, the hydrogen transfer from the methyl group to the terminal oxygen of carbonyl oxide. In this case, the water acts as a catalyst and this reaction can contribute to the atmospheric formation of a hydroxyl radical. Carbonyl oxides with electron withdrawing Substituents and zwitterionic character have low energy barriers and react fast, whereas carbonyl oxides with electron releasing Substituents have high energy barriers and react slowly. The position of the Substituents plays also an important role and carbonyl oxides having a hydrogen atom Substituent in syn react faster than carbonyl oxides having a hydrogen atom Substituent in anti. The differences in the reactivity of different substituted carbonyl oxides raise up to ten orders of magnitude and the branching ratios for the two different reactions investigated are also reported.

Olaf Wiest - One of the best experts on this subject based on the ideXlab platform.

  • Substituent effects in pericyclic reactions of radical cations the ring opening of 3 substituted cyclobutene radical cations
    Journal of Organic Chemistry, 2000
    Co-Authors: David Swinarski, Olaf Wiest
    Abstract:

    The Substituent effects on the ring-opening reaction of cyclobutene radical cations have been studied at the Becke3LYP/6-31G* level of theory. The effect on the reaction energies and activation energies of the concerted and stepwise pathways of electron-donating Substituents such as methyl and methoxy as well as electron-withdrawing Substituents such as nitrile and carboxaldehyde in the 3-position of the cyclobutene is discussed. The exothermicity of the reaction correlates well with the ability of the Substituent to stabilize the 1,3-butadiene radical cation by electron donation or conjugation. The relative stability of the (E) and (Z) isomers of the resulting 1,3-butadiene radical cations depends largely on steric effects. Similarly, steric effects are responsible for the relative energies of the different diastereomeric transition structures. The cyclopropyl carbinyl intermediate of the stepwise pathway resembles the nonclassical carbocation and is stabilized by electron-donating Substituents. In the c...

Kari Neuvonen - One of the best experts on this subject based on the ideXlab platform.

  • effect of 4 substitution on psychotomimetic activity of 2 5 dimethoxy amphetamines as studied by means of different Substituent parameter scales
    Bioorganic & Medicinal Chemistry Letters, 2006
    Co-Authors: Kari Neuvonen, Helmi Neuvonen, Ferenc Fulop
    Abstract:

    Abstract Electron-withdrawing Substituents at position 4 of 2,5-dimethoxy-substituted amphetamines increase, whereas electron-donating Substituents decrease the psychotomimetic activity. The origin of this clearly localized effect is discussed. The uses of modified Hammett Substituent scales ( σ − and σ + ), and especially the good σ + correlation, strongly suggest that electron-donating Substituents decrease the biological activity through a specific effect relating to the extent of the conjugative electron release from the 5-methoxy group to the phenyl ring.

  • Substituent influences on the stability of the ring and chain tautomers in 1 3 o n heterocyclic systems characterization by 13c nmr chemical shifts pm3 charge densities and isodesmic reactions
    Journal of Organic Chemistry, 2001
    Co-Authors: Kari Neuvonen, Helmi Neuvonen, Ferenc Fulop, Andreas Koch, Erich Kleinpeter, Kalevi Pihlaja
    Abstract:

    Substituent effects on the stabilities of the ring and chain forms in a tautomeric equilibrium of five series of 2-phenyloxazolidines or -perhydro-1,3-oxazines possessing nine different substitutions at the phenyl moiety have been studied with the aid of 13C NMR spectroscopy and PM3 charge density and energy calculations. Reaction energies of the isodesmic reactions, obtained from the calculated energies of formation, show that electron-donating Substituents stabilize both the chain and ring tautomers but the effect is stronger on the stability of the chain form than on that of the ring form. The 13C chemical shift changes induced by the phenyl Substituents (SCS) were analyzed by several different single and dual Substituent parameter approaches. The best correlations were obtained by equation SCS = ρFσF + ρRσR . In all cases the ρF values and in most cases also the ρR values were negative at both the CN and C-2 carbons, indicating a reverse behavior of the electron density. This concept could be verified...

Tao Liang - One of the best experts on this subject based on the ideXlab platform.

  • position makes the difference electronic effects in nickel catalyzed ethylene polymerizations and copolymerizations
    Inorganic Chemistry, 2018
    Co-Authors: Tao Liang, Changle Chen
    Abstract:

    A series of phosphine-sulfonate ligands and the corresponding nickel complexes are prepared and characterized. These ligands are specifically designed to bear systematically varied electron-donating and -withdrawing Substituents (H, OMe, NMe2, CF3, and Me). More importantly, these Substituents are installed at different positions on the ligand framework, namely, the para-position of the phenylphosphino group (position X), and para to the arylsulfonate group of the main ligand (position Y). These nickel complexes are highly active single-component catalysts for the polymerization of ethylene. An electron-donating Substituent at position X or an electron-withdrawing Substituent at position Y is beneficial to the properties of these nickel catalysts. Specifically, the catalyst bearing the NMe2 Substituent at position X exhibits high stability and high activity (3.3 × 106 g mol–1 h–1), and catalyzes the formation of polyethylene of high molecular weight (Mn 405 000) and high melting point (Tm 138.5 °C). This ...

  • Position Makes the Difference: Electronic Effects in Nickel-Catalyzed Ethylene Polymerizations and Copolymerizations
    2018
    Co-Authors: Tao Liang, Changle Chen
    Abstract:

    A series of phosphine-sulfonate ligands and the corresponding nickel complexes are prepared and characterized. These ligands are specifically designed to bear systematically varied electron-donating and -withdrawing Substituents (H, OMe, NMe2, CF3, and Me). More importantly, these Substituents are installed at different positions on the ligand framework, namely, the para-position of the phenylphosphino group (position X), and para to the arylsulfonate group of the main ligand (position Y). These nickel complexes are highly active single-component catalysts for the polymerization of ethylene. An electron-donating Substituent at position X or an electron-withdrawing Substituent at position Y is beneficial to the properties of these nickel catalysts. Specifically, the catalyst bearing the NMe2 Substituent at position X exhibits high stability and high activity (3.3 × 106 g mol–1 h–1), and catalyzes the formation of polyethylene of high molecular weight (Mn 405 000) and high melting point (Tm 138.5 °C). This catalyst also mediates the efficient copolymerizations of ethylene with methyl 10-undecenoate, 6-chloro-1-hexene, and trimethoxyvinylsilane