Mechanisms of nucleophilic attack at carbon-nitrogen double bonds. The reaction of aryl N-arylbenzimidates with methoxide ion

1983 ◽  
Vol 36 (6) ◽  
pp. 1259 ◽  
Author(s):  
JE Rowe
Keyword(s):  
Isotope Effects ◽  
Nucleophilic Attack ◽  
Rate Data ◽  
Double Bonds ◽  
Tetrahedral Intermediate ◽  
Methoxide Ion ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

Rate data for the reaction of three series of aryl N-arylbenzimidates with methoxide ion at 303 K are presented. Linear Hammett plots were obtained for each series. Solvent isotope effects have also been measured. The results are interpreted in terms of rate-determining formation of a tetrahedral intermediate, irrespective of the nature of the substituent.

Mechanisms of Nucleophilic Attack at Carbon-Nitrogen Double Bonds. The Reaction of Benzohydrazonoyl Compounds With Methoxide Ion

1995 ◽  
Vol 48 (12) ◽  
pp. 2041 ◽  
Author(s):  
JE Rowe ◽  
DA Papanelopoulos
Keyword(s):  
Nucleophilic Attack ◽  
Rate Data ◽  
Double Bonds ◽  
Elimination Mechanism ◽  
Methoxide Ion

Rate data for the reaction of a number of benzohydrazonoyl compounds with methoxide ion are reported. The stereochemistry of the products was determined by h.p.l.c. The mechanism of the reactions and the stereochemistry of the products resulting from an addition-elimination mechanism are discussed.

Correlation of rates of uncatalyzed and hydroxide-ion catalyzed ketene hydration. A mechanistic application and solvent isotope effects on the uncatalyzed reaction

2000 ◽  
Vol 78 (4) ◽  
pp. 508-515
Author(s):  
John Andraos ◽  
A Jerry Kresge
Keyword(s):  
Carbon Atom ◽  
Rate Constants ◽  
Isotope Effects ◽  
Nucleophilic Attack ◽  
Carbonyl Carbon Atom ◽  
Basic Solution ◽  
Carbonyl Carbon ◽  
Hydroxide Ion ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

Rates of hydration of a number of ketenes were measured in neutral and basic solution using flash photolytic techniques, and rate constants for their uncatalyzed, kuc, and hydroxide-ion catalyzed, kHO, reactions were determined. These results, plus additional data from the literature, were found to provide the remarkably good correlation log kuc = -3.21 + 1.14 log kHO, which spans 10 orders of magnitude in reactivity and includes 31 ketenes. This good correlation implies that uncatalyzed and hydroxide-ion catalyzed ketene hydraton occur by similar reaction mechanisms, which for the hydroxide-ion catalyzed process is known to involve nucleophilic attack on the carbonyl carbon atom of the ketene. Rate constants for phenylhydroxyketene, on the other hand, do not fit this correlation, which suggests that the mechanistic assignment upon which these rate constants are based may not be correct. Solvent isotope effects on these uncatalyzed ketene hydrations are weak; most are less than kH/kD = 2. It is argued that these isotope effects are largely, if not entirely, secondary in nature and that they are consistent with both a reaction mechanism in which nucleophlic attack of a single water molecule on the ketene carbonyl carbon atom produces a zwitterionic intermediate and also a mechanism that avoids this intermediate by passing through a cyclic transition state involving several water molecules.Key words: ketene hydration, rate correlation, nucleophilic attack, solvent isotope effects, phenylhydroxyketene.

Studies in solvolysis. Part I. The neutral hydrolysis of some alkyl trifluoroacetates in water and deuterium oxide

1968 ◽  
Vol 46 (18) ◽  
pp. 2887-2894 ◽  
Author(s):  
June G. Winter ◽  
J. M. W. Scott
Keyword(s):  
Deuterium Oxide ◽  
Isotope Effects ◽  
Activation Process ◽  
Rate Data ◽  
Methyl Ethyl ◽  
Light Water ◽  
Carbonium Ion ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The temperature dependence of the rates of neutral hydrolysis of a series of alkyl trifluoroacetates (CF3COOR; R = methyl, ethyl, s-propyl, t-butyl) has been determined in both light and heavy water. From these studies the thermodynamic parameters (ΔH≠, ΔS≠) which characterize the activation process have been calculated. Sufficient rate data have been obtained in the case of the ethyl ester to calculate the heat capacity of activation (ΔCP≠) for the hydrolysis of this compound in light water. Both the entropies and enthalpies of activation as well as the solvent isotope effects are consistent with the proposal that the primary and secondary esters react by an acyl–oxygen BAc2 mechanism, in contrast to the tertiary ester, which appears to react either by a carbonium ion (SN1) process or by a route which combines both the BAc2 and SN1 paths.

Article

1999 ◽  
Vol 77 (4) ◽  
pp. 459-462
Author(s):  
J Andraos ◽  
Y Chiang ◽  
S J Eustace ◽  
A J Kresge ◽  
S W Paine ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Carbonyl Group ◽  
Flash Photolysis ◽  
Isotope Effects ◽  
Nucleophilic Attack ◽  
Hydroxide Ion ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

Five ketenes, phenyl(ethyl)ketene, phenyl(methylthio)ketene, diphenylketene, pentafluorophenylketene, and 1-naphthylketene, were generated flash photolytically and solvent isotope effects (H2O vs. D2O) on their hydroxide-ion-catalyzed hydration in aqueous solution were determined. The values obtained are all weakly inverse and closely similar (kHO/kDO = 0.76-0.97), as expected for these fast, hydroxide-ion-consuming reactions, known to proceed by nucleophilic attack of hydroxide on the ketene carbonyl group. The characteristic magnitude of these isotope effects should prove useful in identifying new examples of this reaction.Key words: ketenes, flash photolysis, photo-Wolff reaction, solvent isotope effects on hydroxide ion consumption.

scholarly journals Rate and Product Studies with 1-Adamantyl Chlorothioformate under Solvolytic Conditions

2021 ◽  
Vol 22 (14) ◽  
pp. 7394
Author(s):  
Kyoung Ho Park ◽  
Mi Hye Seong ◽  
Jin Burm Kyong ◽  
Dennis N. Kevill
Keyword(s):  
Rate Constants ◽  
Isotope Effects ◽  
Ion Pairs ◽  
Carbonyl Sulfide ◽  
Activation Parameters ◽  
Chloride Ions ◽  
Reaction Channels ◽  
Decomposition Pathway ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

A study was carried out on the solvolysis of 1-adamantyl chlorothioformate (1-AdSCOCl, 1) in hydroxylic solvents. The rate constants of the solvolysis of 1 were well correlated using the Grunwald–Winstein equation in all of the 20 solvents (R = 0.985). The solvolyses of 1 were analyzed as the following two competing reactions: the solvolysis ionization pathway through the intermediate (1-AdSCO)+ (carboxylium ion) stabilized by the loss of chloride ions due to nucleophilic solvation and the solvolysis–decomposition pathway through the intermediate 1-Ad+Cl− ion pairs (carbocation) with the loss of carbonyl sulfide. In addition, the rate constants (kexp) for the solvolysis of 1 were separated into k1-Ad+Cl− and k1-AdSCO+Cl− through a product study and applied to the Grunwald–Winstein equation to obtain the sensitivity (m-value) to change in solvent ionizing power. For binary hydroxylic solvents, the selectivities (S) for the formation of solvolysis products were very similar to those of the 1-adamantyl derivatives discussed previously. The kinetic solvent isotope effects (KSIEs), salt effects and activation parameters for the solvolyses of 1 were also determined. These observations are compared with those previously reported for the solvolyses of 1-adamantyl chloroformate (1-AdOCOCl, 2). The reasons for change in reaction channels are discussed in terms of the gas-phase stabilities of acylium ions calculated using Gaussian 03.

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