Réactivité nucléophile des cyclanones: influence de la stéréochimie cis/trans en série bicyclique

1982 ◽  
Vol 60 (18) ◽  
pp. 2355-2357 ◽  
Author(s):  
C. Agami ◽  
T. Rizk ◽  
R. Durand ◽  
P. Geneste
Keyword(s):  
Trans Isomer ◽  
Rate Constants ◽  
Nucleophilic Addition ◽  
Acidic Medium ◽  
Conformation Equilibrium ◽  
Bicyclic Ketones

The relative reactivities of a number of cis/trans pairs of bicyclic ketones in the 1- and 2-decalone series (2-decalone; 10-methyl-2-decalone; 9-methyl-1-decalone; and 3,10-dimethyl-2-decalone) have been studied for the nucleophilic addition of hydroxylamine in acidic medium. The results obtained as well as the rate constants for neutral or acid catalysed addition always reveal a slight preference for the trans-isomer (× 2.4). This result agrees with the proposal that preferential equatorial attack of a nucleophile is caused by conformational factors related to a steroid [Formula: see text] non-steroid conformation equilibrium in the cis-isomers. [Journal Translation]

Kinetics of hydrolysis of peroxodisulphate ions in acidic medium to peroxomonosulphuric acid

1981 ◽  
Vol 46 (5) ◽  
pp. 1229-1236 ◽  
Author(s):  
Jan Balej ◽  
Milada Thumová
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Acidic Medium ◽  
Measured Data ◽  
Molar Ratios ◽  
Starting Solution ◽  
Kinetics Of Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of

The rate of hydrolysis of S2O82- ions in acidic medium to peroxomonosulphuric acid was measured at 20 and 30 °C. The composition of the starting solution corresponded to the anolyte flowing out from an electrolyser for production of this acid or its ammonium salt at various degrees of conversion and starting molar ratios of sulphuric acid to ammonium sulphate. The measured data served to calculate the rate constants at both temperatures on the basis of the earlier proposed mechanism of the hydrolysis, and their dependence on the ionic strength was studied.

THE KINETICS OF THE ALKALINE HYDROLYSES OF DIMETHYL TEREPHTHALATE AND THE TRANS ISOMER OF DIMETHYL 1,4-CYCLOHEXANEDICARBOXYLATE IN DIOXANE–WATER MIXTURES

1962 ◽  
Vol 40 (9) ◽  
pp. 1826-1829 ◽  
Author(s):  
W. J. Svirbely ◽  
Patricia A. Cunniff
Keyword(s):  
Dielectric Constant ◽  
Trans Isomer ◽  
Rate Constants ◽  
Dimethyl Terephthalate ◽  
Kinetics Of

The kinetics of the alkaline hydrolyses of dimethyl terephthalate and trans-dimethyl 1,4-cyclohexanedicarboxylate was studied in dioxane–water mixtures varying in dielectric constant from 60 to 11. The effect of the medium on the mechanism and rate constants is, in general, similar to that previously observed in the study of the alkaline hydrolyses of aliphatic diesters.

Detection and kinetic characterization of SNV intermediates. Reactions of thiomethoxybenzylidene Meldrum's acid with thiolate ions, alkoxide ions, OH-, and water in aqueous DMSO

1999 ◽  
Vol 77 (5-6) ◽  
pp. 584-594 ◽  
Author(s):  
Claude F Bernasconi ◽  
Rodney J Ketner ◽  
Xin Chen ◽  
Zvi Rappoport
Keyword(s):  
Rate Constants ◽  
Nucleophilic Addition ◽  
Equilibrium Constants ◽  
Intrinsic Rate ◽  
Nucleophilic Attack ◽  
Meldrum's Acid ◽  
Meldrum’S Acid ◽  
Nucleophilic Vinylic Substitution ◽  
Steady State Levels ◽  
Vinylic Substitution

The reaction of thiomethoxybenzylidene Meldrum's acid (5-SMe) with thiolate and alkoxide ion nucleophiles is shown to proceed by the two-step addition-elimination SNV mechanism in which the tetrahedral intermediate accumulates to detectable levels. For the reactions with thiolate ions, rate constants for nucleophilic addition (k1RX), its reverse (k-1RX), and for conversion of the intermediate to products (k2RX) were determined. For the reactions with alkoxide ions, only k1RX and k-1RX could be obtained; the intermediate in these reactions did not yield the expected substitution products, and hence no k2RX values could be determined. The reactions with OH- and water are believed to follow the same mechanism, but the respective intermediates remain at steady-state levels, and only k1OH and k1H²O for nucleophilic attack on 5-SMe were measurable. New insights regarding structure-reactivity behavior in SNV reactions are gained from comparisons of rate and equilibrium constants in the reactions of 5-SMe with the corresponding parameters in the reactions of methoxybenzylidene Meldrum's acid (5-OMe) and benzylidene Meldrum's acid (5-H). In particular, the relative importance of steric and pi-donor effects of the MeS vs. MeO group in 5-SMe and 5-OMe, respectively, and their role in affecting the intrinsic rate constants for nucleophilic addition, has been clarified by these comparisons. Our results also add support to a previous suggestion that soft-soft type interactions tend to increase intrinsic rate constants for thiolate ion addition to vinylic substrates, especially 5-SMe with the soft MeS group.Key words: nucleophilic vinylic substitution, intrinsic rate constants, transition state imbalances, steric/pi-donor/anomeric effects.

Effect of Substituents and Solvents on Phenol-Isocyanate Urethane Reaction

2010 ◽  
Vol 150-151 ◽  
pp. 23-26 ◽  
Author(s):  
Peng Fei Yang ◽  
Yong De Han ◽  
Tian Duo Li
Keyword(s):  
Hydrogen Atom ◽  
Nitrogen Atom ◽  
Rate Constants ◽  
Nucleophilic Addition ◽  
Reaction Rate ◽  
Effect Of Substituents ◽  
Reaction Rate Constants ◽  
Ft Ir ◽  
Polarity Of Solvents

In this study, the urethane reaction of several phenols with isocyanate was monitored with in-situ FT-IR. Reaction rate constants were calculated out to investigate the effect of substituents in phenols, as well as the polarity of different solvents. It showed that the polarity of solvents largely affected the reaction rate even without catalyst. The reactivity increased in the following order: Xylene < 1,4-Dioxane < Cyclohexanone. Furthermore, an electron-withdrawing substituent in phenols increased the reactivity of hydroxyl with isocyanate. The reason may be that the H-O bond in phenols could be easily polarized under the influence of electron-withdrawing substituent, where the hydrogen atom was more likely to attack the nitrogen atom of -NCO, thus the nucleophilic addition happened easier.

Rate constants for the addition of the enolate ion of acetone to quinolinium and acridinium cations

1990 ◽  
Vol 68 (10) ◽  
pp. 1762-1768 ◽  
Author(s):  
John W. Bunting ◽  
Cynthia Fu ◽  
James W. Tam
Keyword(s):  
Ionic Strength ◽  
Aqueous Solutions ◽  
Rate Constants ◽  
Nucleophilic Addition ◽  
Ph Dependence ◽  
Adduct Formation ◽  
Kinetic Control ◽  
Thermodynamic Control ◽  
Hydroxide Ion ◽  
Kinetically Controlled

The reaction of acetone with four heteroaromatic cations (10-methylacridinium (1), 3-aminocarbonyl-1-methylquinolinium (2a), 3-cyano-1-methylquinolinium (2b), and 3-bromo-1-methylquinolinium (2c)) has been investigated in basic aqueous solutions (pH 9–12, ionic strength 0.1, 25 °C). For each of 2a and 2b, the kinetically controlled product is a 35:65 mixture of the C-2 and C-4 enolate ion adducts; the C-2 adduct subsequently isomerizes to give the C-4 adduct as the only observable species under thermodynamic control. For 2c, the C-2 enolate adduct appears to be favoured both kinetically and thermodynamically. Under kinetic control, the pH-dependence of adduct formation from each cation is consistent with rate-determining attack of the enolate ion upon the heterocyclic cation. Comparisons of regiochemical control of acetone enolate ion attack with hydroxide ion attack upon these same cations indicate that acetone enolate ion shows a more pronounced preference for C-4 attack over C-2 attack than does hydroxide ion. The thermodynamically controlled regiochemistry is similar for each of these two nucleophiles. Keywords: nucleophilic addition, regioselectivity, kinetic control, thermodynamic control, quinolinium cations.

Electroreduction of 1-methyl 5-nitroindole, 5-nitrobenzofurane, and 5-nitrobenzothiophene in acidic and basic hydroorganic media: Generation and trapping of iminoquinone-type intermediates and electrosynthesis of ring-substituted amino derivatives

2003 ◽  
Vol 81 (10) ◽  
pp. 1108-1118 ◽  
Author(s):  
Luc Bouchard ◽  
Ian Marcotte ◽  
Jean Marc Chapuzet ◽  
Jean Lessard
Keyword(s):  
Key Words ◽  
Nucleophilic Addition ◽  
Acidic Medium ◽  
Cycloaddition Reaction ◽  
Am1 Calculations ◽  
Electrolytic Solution ◽  
Preparative Electrolysis ◽  
Regioselective Addition ◽  
Amino Derivatives ◽  
Type Intermediate

Preparative electrolysis of 1-methyl-5-nitroindole (1b, X = NCH3), 5-nitrobenzofurane (1c, X = O), and 5-nitrobenzothiophene (1d, X = S) at Hg, in acidic hydromethanolic media, leads to the formation of the corresponding 4-substituted amino derivatives 5, which result from the 100% regioselective addition to iminoquinone-type intermediate 4 of methanol or of any other good nucleophile present in the electrolytic solution. In acidic medium, the iminoquinonium intermediates 4b and 4c were trapped in a cycloaddition reaction with cyclopentadiene added to the electrolysis medium. The regiochemistry of the nucleophilic addition is discussed in light of AM1 calculations. Key words: 1-methyl-5-nitroindole, 5-nitrobenzofurane, 5-nitrobenzothiophene, iminoquinone, electrosynthesis.

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