Steric effects in quaternizations. Alkylation of pyridine, thiazole, isothiazole and some benzologues with methyl, ethyl and isopropyl iodides

1976 ◽  
Vol 29 (8) ◽  
pp. 1745 ◽  
Author(s):  
LW Deady ◽  
DC Stillman
Keyword(s):  
Steric Hindrance ◽  
Electronic Effect ◽  
Alkyl Halide ◽  
Steric Effects ◽  
Methyl Ethyl ◽  
Rate Retardation

Results of quaternization reactions in sulpholane at 65� are reported. A large steric hindrance is noted for quinoline relative to pyridine. A much smaller variation in rate with change in alkyl halide is seen in the benzothiazole/thiazole pair. Steric effects are very small and the rate retardation resulting from benzofusion is ascribed largely to an electronic effect. 2,l-Benzisothiazole reacts at essentially the same rate as isothiazole under these conditions.

scholarly journals On the nature of the electronic effect of multiple hydroxyl groups in the 6-membered ring – the effects are additive but steric hindrance plays a role too

2017 ◽  
Vol 15 (5) ◽  
pp. 1164-1173 ◽  
Author(s):  
Christian Marcus Pedersen ◽  
Mikael Bols
Keyword(s):  
Steric Hindrance ◽  
Electronic Effect ◽  
Membered Ring ◽  
Steric Effects ◽  
Hydroxyl Groups ◽  
Base Strength ◽  
Electronic And Steric Effects

Electronic and steric effects each play important roles in determining the base strength in piperidines.

RATES OF POLYMERIZATION OF ACRYLATES AND METHACRYLATES IN EMULSION SYSTEMS

1964 ◽  
Vol 42 (4) ◽  
pp. 825-829 ◽  
Author(s):  
K. G. McCurdy ◽  
K. J. Laidler
Keyword(s):  
Steric Hindrance ◽  
Steric Effects ◽  
Hydroxyl Group ◽  
Methyl Ethyl ◽  
Initial State ◽  
Emulsion Systems

The microcalorimeter has been used to obtain rates of polymerization of a number of monomers in emulsion systems. The rates with the acrylates are consistently higher than those with the methacrylates, and this is attributed to less steric hindrance. Low rates found with monomers containing a hydroxyl group are explained as due to solvation in the initial state. In both the acrylates and methacrylates the rates go through a maximum as one goes up the series methyl: ethyl: butyl: hexyl. This is discussed in terms of inductive and steric effects.

Michael Additions of Benzotriazole-Stabilized Carbanions. A Review

1998 ◽  
Vol 63 (5) ◽  
pp. 599-613 ◽  
Author(s):  
Alan R. Katritzky ◽  
Ming Qi
Keyword(s):  
Steric Hindrance ◽  
Electronic Effect ◽  
Steric Effects ◽  
Unsaturated Ketone ◽  
Electronic Effects ◽  
Michael Additions ◽  
Unsaturated Aldehydes ◽  
Michael Acceptor ◽  
Michael Acceptors ◽  
Electron Withdrawing Group

The 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors is reviewed. The selectivity between 1,4- and 1,2-addition depends significantly on the electronic effect of the carbanion (usually lithium is the counterion), the type of the Michael acceptor, and steric effects. Steric hindrance of the benzotriazolyl group probably enhances the regioselectivity. Normally, 1,4-additions to α,β-unsaturated ketone or ester are observed for carbanions stabilized by a benzotriazolyl group and an electron-withdrawing group (e.g. aryl, vinyl, carbonyl). For α,β-unsaturated aldehydes as Michael acceptors, 1,2-addition is more likely, except where electronic effects are very strong. A review with 39 references.

Synthesis of Silyl Iron Dinitrogen Complexes for Activation of Dihydrogen and Catalytic Silylation of Dinitrogen

2021 ◽  
Author(s):  
Guoliang Chang ◽  
Peng Zhang ◽  
Wenjing Yang ◽  
Yanhong Dong ◽  
Shangqing Xie ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
Electronic Effect ◽  
Dinitrogen Complexes ◽  
First Time

Three novel iron dinitrogen hydrides, [FeH(iPr-PSiMeP)(N2)(PMe3)] (1), [FeH(iPr-PSiPhP)(N2)(PMe3)] (2), and [FeH(iPr-PSiPh)(N2)(PMe3)] (3), supported by silyl ligand are synthesized for the first time by changing the electronic effect and steric hindrance...

Effect of Alkyl Group Structure on Cure Characteristics of N,N-Dialkylthio-Carbamyl-N′,N′-Dialkylsulfenamide Vulcanization Accelerators

1974 ◽  
Vol 47 (4) ◽  
pp. 906-910 ◽  
Author(s):  
R. D. Taylor
Keyword(s):  
Carbon Atom ◽  
Steric Hindrance ◽  
Alkyl Group ◽  
Group Structure ◽  
Substituent Effects ◽  
Steric Effects ◽  
Alkyl Groups ◽  
Inductive Effects ◽  
Cure Rates ◽  
Alpha Carbon

Abstract Wide variations in scorch times and cure rates can be attained with tetraalkylthiocabamylsulfenamides through variation in alkyl groups. Substituent effects are substantial on either the carbamate nitrogen or on the sulfenamide nitrogen. Both inductive effects and steric effects influence the scorch times and cure rates. Positive inductive effects shorten scorch times and increase cure rates. Steric hindrance at the sulfenamide nitrogen increases the scorch time. Branching at the carbon atom beta to the nitrogen has a larger effect on scorch time than branching at the alpha carbon. Thiocarbamylsulfenamides can give appreciably higher cure rates and cure efficiencies than their benzothiazole sulfenamide analogs.

Effect of Third Monomer Type and Content on Peroxide Crosslinking Efficiency of EPDM

2003 ◽  
Vol 76 (1) ◽  
pp. 132-144 ◽  
Author(s):  
Martin van Duin ◽  
Herman G. Dikland
Keyword(s):  
Molecular Weight ◽  
Steric Hindrance ◽  
Radical Addition ◽  
Steric Effects ◽  
Low Molecular Weight ◽  
Comprehensive Overview ◽  
Model Studies ◽  
The Third ◽  
Peroxide Curing ◽  
Weight Model

Abstract Peroxide crosslinking of EPDM is commonly applied in rubber practice. Although the presence of a diene termonomer is not a prerequisite for peroxide crosslinking, it does provide a significant increase of the peroxide crosslinking efficiency. Different explanations for the effect of the type and the amount of the third monomer on the peroxide curing efficiency have been put forward; but, a comprehensive overview and an acceptable explanation of all the effects observed are still lacking. In the present paper, this gap is filled by combining results from low-molecular-weight model studies and rheometer experiments with information from the literature. It is shown that peroxide crosslinking of EPDM proceeds via the combination of two EPDM macro-radicals and the addition of an EPDM macro-radical to the residual EPDM unsaturation. The extent to which the latter radical addition occurs, is governed by the amount of the third monomer and by the steric hindrance of the residual unsaturation of the EPDM, i.e. the lower the number of ipso- and β- alkyl substituents on the unsaturation, the higher the rate of addition. This explains why EPDMs containing termonomers with terminal unsaturations are more reactive than those with internal unsaturations. The same approach was followed to assess the peroxide curing efficiency of polydiene elastomers. It was found that the same steric effects govern peroxide crosslinking of polydiene elastomers, such as NR, IR and BR.

Stabilities of Carbonium-Ions. IV. Steric Effects in the Solvolysis of Substituted Diphenylmethyl Chlorides

1986 ◽  
Vol 39 (4) ◽  
pp. 625 ◽  
Author(s):  
R Bolton ◽  
RE Burley ◽  
NJ Williams
Keyword(s):  
Electronic Effect ◽  
Substituent Effects ◽  
Methyl Chloride ◽  
Steric Effects ◽  
Methyl Groups ◽  
Hydrogen Atoms ◽  
Carbonium Ions ◽  
Rate Of Reaction ◽  
Resonance Stabilization ◽  
Planar Transition

The replacement of ortho-hydrogen atoms by methyl groups in diphenylmethyl chloride has three distinguishable results upon the rate of solvolysis . Firstly, the alkyl groupactivates by its electronic effect; secondly, steric interactions diminish all observed substituent effects regardless of the position of the substituent in the aryl system; and thirdly, steric acceleration of the solvolysis can be seen in the rate of reaction of bis (2,6-dimethylphenyl)methyl chloride. The ortho-methyl substituents inhibit the formation of the planar transition state necessary to allow the greatest resonance stabilization by the aryl substituents of the incipient carbocation. Greater degrees of twist are reflected both in the variations in the rates of solvolysis of the poly(orthomethyl ) diphenylmethyl chlorides and in the consistent fall in the value of p+ with successive ortho-substitution.

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