Solvent effects in the solvolysis of aryldi-tert-butylcarbinyl-p-nitrobenzoates in aqueous acetic acid. Substituent effects on transition state charge separation

1975 ◽  
Vol 40 (22) ◽  
pp. 3303-3304 ◽  
Author(s):  
John S. Lomas ◽  
Jacques E. Dubois
Keyword(s):  
Acetic Acid ◽  
Transition State ◽  
Solvent Effects ◽  
Charge Separation ◽  
Substituent Effects ◽  
Aqueous Acetic Acid ◽  
State Charge

Thermolysis of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones in solution. Products, kinetics, substituent effects, and solvent effects

1981 ◽  
Vol 59 (1) ◽  
pp. 100-105 ◽  
Author(s):  
Lubomira M. Cabelkova-Taguchi ◽  
John Warkentin
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Charge Separation ◽  
Substituent Effects ◽  
Activation Parameters ◽  
Oxidative Cyclization ◽  
First Order ◽  
Temperature Range ◽  
Aryl Amine ◽  
First Order Kinetics

A series of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones (Ar = C6H5, p-C6H4CH3, p-C6H4OCH3, p-C6H4Cl, and p-C6H4Br) were prepared from the corresponding 4-arylsemicarbazones of acetone by oxidative cyclization on alumina. The triazolinones decompose in solution to N2, CO, and isopropylidene aryl amine, with first order kinetics, in the temperature range 148–200 °C. Average activation parameters are ΔH≠ = 35 kcal mol−1 and ΔS≠ = 8 cal K−1 mol−1. Substituent effects are correlated through σ-constants but the thermolyses are relatively insensitive to substituents, with ρ = −0.17 at 172.5 °C. Solvent effects indicate a transition state that is less polar than the ground state.It is tentatively concluded that the triazolinone fragmentation, like the analogous thermolysis of a Δ3-1,3,4-oxadiazolin-2-one, may be a fully-concerted but nonsynchronous process with a transition state involving little, if any, charge separation. Other mechanisms, except for those involving highly polar (e.g. zwitterionic) transition states, have not been ruled out.

Chlorination of 2-Phenoxypropanoic Acid with NCP in Aqueous Acetic Acid:  Using a Novel Ortho−Para Relationship and the Para/Meta Ratio of Substituent Effects for Mechanism Elucidation

2007 ◽  
Vol 72 (14) ◽  
pp. 5327-5336 ◽  
Author(s):  
Manuel A. P. Segurado ◽  
João Carlos R. Reis ◽  
Jaime D. Gomes de Oliveira ◽  
Senthamaraikannan Kabilan ◽  
Manohar Shanthi
Keyword(s):  
Acetic Acid ◽  
Substituent Effects ◽  
Aqueous Acetic Acid

Kinetics of reactions of para-substituted phenyl isocyanates with amines and alcohols

1991 ◽  
Vol 56 (8) ◽  
pp. 1662-1670 ◽  
Author(s):  
Ivan Danihel ◽  
Falk Barnikol ◽  
Pavol Kristian
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Rate Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Stopped Flow ◽  
Partial Charges ◽  
Hammett Correlation ◽  
One Step ◽  
Kinetics Of

The reaction of para-substituted phenyl isocyanates with amines and alcohols was studied by stopped-flow method. The Hammett correlation obtained showed that the sensitivity of the above mentioned reactions toward substituent effects is the same as that of analogous reactions of phenyl isothiocyanates (ρ ~ 2). The rate constants of these reactions were found to be affected more by steric effects than by solvent effects. An one step multicentre mechanism with partial charges in transition state has been proposed for the title reactions.

Chlorination of N-Phenylbenzenesulfonamides with NCP in Aqueous Acetic Acid. Using the para/meta Ratio of Substituent Effects for Mechanism Elucidation

2004 ◽  
Vol 69 (12) ◽  
pp. 2253-2275 ◽  
Author(s):  
João Carlos R. Reis ◽  
Manuel A. P. Segurado ◽  
Jaime D. Gomes de Oliveira ◽  
Senthamaraikannan Kabilan ◽  
Krishnasamy Suganya
Keyword(s):  
Acetic Acid ◽  
Nitrogen Atom ◽  
Rate Constants ◽  
Substituent Effects ◽  
Aqueous Acetic Acid ◽  
Isokinetic Temperature ◽  
Isokinetic Relationship ◽  
Rate Determining Step ◽  
Different Temperatures ◽  
Energy Ratios

Rate constants were measured for the oxidative chlorination reaction of N-phenylbenzenesulfonamide 2 and twelve ortho-, nine meta- and twelve para-substituted derivatives in the aniline moiety, using 1-chloro-3-methyl-2,6-diphenylpiperidin-4-one (1) as chlorinating agent. The kinetics was run in 50% (v/v) aqueous acetic acid acidified with perchloric acid under pseudo-first-order conditions with respect to 1 at five different temperatures between 298 and 318 K. The dependence of rate constants on temperature was analysed in terms of the isokinetic relationship (IKR). The resulting isokinetic temperature was estimated to be 513 K. Using the Linert's theory of the IKR, the experimental isokinetic temperature was interpreted as evidence for the preferential involvement of water molecules in the formation of activated complexes. The dependence of the rate constants on the substituents was analysed using the tetralinear extension of the Yukawa-Tsuno equation for the effects of meta and para substituents. A positively charged transition state was suggested by an experimental value r+ = 0.39 for the resonance demand, which was found to be insensitive to temperature variation. The parameter λ for the para/meta ratio of substituent effects was estimated to be 0.952. The electrostatic modelling of λ values was re-examined in the light of the recent calculations of the energies of interaction between charged and/or dipolar groups by Exner and Böhm. Based on energy ratios, the electrostatic method was shown to remain valid for the purpose of modelling λ values. The experimental λ value for the reaction indicates the formation of an activated complex possessing an electric charge in the vicinity of the nitrogen atom of the substrate. The electrophilic attack on the substrate nitrogen atom by the protonated chlorinating reagent has been proposed as the rate-determining step, with the last step being the fast rearrangement of the intermediate N-chloro-N-phenylbenzenesulfonamidium cation into the products.

Substituent Rate Effects in Sigmatropic Homodienyl [1,5]-Hydrogen Migrations

1990 ◽  
Vol 43 (8) ◽  
pp. 1357 ◽  
Author(s):  
GG Pegg ◽  
GV Meehan
Keyword(s):  
Transition State ◽  
Charge Separation ◽  
Substituent Effect ◽  
Substituent Effects ◽  
Aryl Group ◽  
Rate Enhancement ◽  
Polar Substituent ◽  
Rate Effects ◽  
Electronic Perturbation

The small but systematic polar substituent effect on the rates of [1,5]- homodienyl hydrogen migrations previously observed for the series of alkenylcyclopropane substrates (1) has been further explored through two additional substrate series (4) and (6) bearing the aryl probe at C4 and at the migration origin C1 respectively. However, negligible substituent effects were apparent at these positions. It now seems that the substituent effect originally observed at C5 reflects electronic perturbation by the substituent, rather than an inherent charge separation in the transition state for homodienyl rearrangement. The aryl group at C1 of the series (6) does, however, afford a substantial rate enhancement relative to the parent cis-1-methyl-2-vinylcyclopropane. In addition, exclusive formation of (1E,4Z)-1-arylhexa-1,4-diene rearrangement products is observed. These kinetic and stereochemical observations are interpreted in terms of a stereoelectronically favoured equatorial conformation for the aryl group in the transition state for rearrangement.

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