Catalysis in ester cleavage. III. Solvent isotope effects and transition-state solvation in the basic methanolysis of esters

1969 ◽  
Vol 91 (8) ◽  
pp. 2045-2047 ◽  
Author(s):  
Carl G. Mitton ◽  
Michael Gresser ◽  
Richard L. Schowen
Keyword(s):  
Transition State ◽  
Isotope Effects ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

Heavy Atom Kinetic Isotope Effects in HCN Elimination from Some Tricyanides in Methanol [1]

1978 ◽  
Vol 33 (12) ◽  
pp. 1496-1502
Author(s):  
Fouad M. Fouad ◽  
Patrick G. Farrell
Keyword(s):  
Transition State ◽  
Opposite Direction ◽  
Isotope Effects ◽  
Heavy Atom ◽  
Transition States ◽  
Kinetic Isotope Effects ◽  
The Other ◽  
Kinetic Isotope ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

AbstractRates of HCN elimination from polycyanides N,N-dimethyl-4-(1,2,2-tricyanoethyl)-aniline (1), 9-cyano-9-dicyanomethyl fluorene (2), 1,1-diphenyl-1,2,2-tricyanoethane (3), and 2-phenyl-1,1,2-tricyanopropane (4) have been studied in methanol. Elimination from 1 occurs via (E 1 c B)R, mechanism. On the other hand olefin formation from 2-4 has been shown to occur via (E 1)anion pathway. Heavy atom kinetic isotope effects indicated that product stability is not the sole factor controlling the transition state geometries. Values of k12/k14 were found to be in the order 2 > 3 > 4 > 1 which implied transition states with more carbanion-like structure in the opposite direction. Solvent isotope effects and enthalpies of activation were also determined and discussed in terms of transition states geometries.

Solvent isotope effects as a probe of general catalysis and solvation in phosphoryl transfer

1996 ◽  
Vol 74 (6) ◽  
pp. 931-938 ◽  
Author(s):  
Clinton D. Bryan ◽  
K. Barbara Schowen ◽  
Richard L. Schowen
Keyword(s):  
Ionic Strength ◽  
Transition State ◽  
Rate Constant ◽  
Relative Rate ◽  
Isotope Effects ◽  
Phosphoryl Transfer ◽  
Relative Rate Constant ◽  
Nitrophenyl Phosphate ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

Phosphoryl transfer to methanol from tris(p-nitrophenyl) phosphate (PNNN), methyl bis(p-nitrophenyl) phosphate (PMNN), and dimethyl p-nitrophenyl phosphate (PMMN) exhibits general base catalysis by acetate ion but no detectable catalysis by acetic acid. For PNNN, acetate catalysis produces normal solvent isotope effects kROH/kROD of 1.68 ± 0.01 at high ionic strength (0.475) and 1.77 ± 0.04 at low ionic strength (0.048). A linear proton inventory indicates most simply that the isotope effect arises from a one-proton catalytic bridge in the transition state, although this model cannot strongly be distinguished from a generalized solvation effect. Reactions of methoxide ions produce slight inverse isotope effects kROD/kROH of 1.1–1.2, far smaller than the inverseeffect of about 2.5 expected for complete and uncompensated desolvation of the reactant-state methoxide ion. The transition state is thus stabilized by substantial interaction with the solvent. The proton inventory for the least reactive substrate PMMN (relative rate constant 1) is suggestive of transition-state stabilization by a combination of one-proton catalytic bridge(s) and distributed sites, while the proton inventory for the most reactive substrate PNNN (relative rate constant 1388) suggests only generalized transition-state solvation (many distributed sites); the proton inventory for PMNN, a substrate of intermediate reactivity (relative rate constant 60), suggests an intermediate situation. The data are consistent with a model in which transition states with exterior concentrations of charge favor stabilization of the charge by isotope-fractionating one-proton bridges, while transition states with distributed charge favor stabilization of the charge by many distributed sites. Key words: phosphoryl transfer, proton inventories, solvent isotope effects.

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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