Réactions de substitution homolytique. V. Stéréosélectivité de différents radicaux cyclohexyles

1976 ◽  
Vol 54 (6) ◽  
pp. 905-909 ◽  
Author(s):  
Michel Gruselle ◽  
Jacques Fossey ◽  
Daniel Lefort ◽  
Claude Lamarre ◽  
Jean-Claude Richer
Keyword(s):  
Steric Hindrance ◽  
Substitution Reaction ◽  
Steric Effects ◽  
Relative Importance ◽  
Peroxy Acid ◽  
Radical Site ◽  
Peroxy Acids ◽  
Homolytic Substitution ◽  
Thermal Decarboxylation ◽  
As If

The influence of the environment near the radical site on the stereoselectivity of the homolytic substitution reaction of variously substituted cyclohexyl radicals on the peroxidic oxygen of a peroxy acid has been studied using the thermal decarboxylation of peroxy acids. This reaction leads to stereoisomeric alcohols[Formula: see text]The radical behaves as if it were planar and, in general, an axial approach of the reagent is strongly favoured except when substituents increase the steric hindrance of the radical.The stereoselectivity is explained in terms of the relative importance of steric effects (for the axial approach) and of bond interactions (for the equatorial approach). It also depends on the flexibility of the ring. [Journal translation]

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.

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.

Steric Effects in Fast Metal Complex Substitution Reaction I1

1966 ◽  
Vol 88 (20) ◽  
pp. 4610-4615 ◽  
Author(s):  
Kenneth Kustin ◽  
Robert F. Pasternack ◽  
Elliot M. Weinstock
Keyword(s):  
Metal Complex ◽  
Substitution Reaction ◽  
Steric Effects

The relative importance of primary steric effects in acetylation of benzene and thiophen derivatives

1971 ◽  
Vol 12 (7) ◽  
pp. 611-612 ◽  
Author(s):  
Sergio Clementi ◽  
Paolo Linda ◽  
Marco Vergoni
Keyword(s):  
Steric Effects ◽  
Relative Importance
Sign in / Sign up

Export Citation Format

Share Document