Phosphoryl-transfer reactions of phosphodiesters: characterization of transition states by heavy-atom isotope effects

1991 ◽  
Vol 113 (15) ◽  
pp. 5835-5841 ◽  
Author(s):  
Alvan C. Hengge ◽  
W. W. Cleland
Keyword(s):  
Isotope Effects ◽  
Heavy Atom ◽  
Transition States ◽  
Transfer Reactions ◽  
Phosphoryl Transfer

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.

Understanding the transition states of phosphodiester bond cleavage: Insights from heavy atom isotope effects

Biopolymers ◽  
2003 ◽  
Vol 73 (1) ◽  
pp. 110-129 ◽  
Author(s):  
Adam G. Cassano ◽  
Vernon E. Anderson ◽  
Michael E. Harris
Keyword(s):  
Bond Cleavage ◽  
Isotope Effects ◽  
Heavy Atom ◽  
Transition States ◽  
Phosphodiester Bond

Hydrolysis of Phosphotriesters:  Determination of Transition States in Parallel Reactions by Heavy-Atom Isotope Effects

2001 ◽  
Vol 123 (38) ◽  
pp. 9246-9253 ◽  
Author(s):  
Mark A. Anderson ◽  
Hyunbo Shim ◽  
Frank M. Raushel ◽  
W. W. Cleland
Keyword(s):  
Isotope Effects ◽  
Heavy Atom ◽  
Transition States ◽  
Parallel Reactions ◽  
Hydrolysis Of

Probing transition states of concerted rearrangements for synchronicity: Use of heavy-atom kinetic isotope effects

1986 ◽  
Vol 138 (1-2) ◽  
pp. 107-112
Author(s):  
Henry J. Shine ◽  
Lidia Kupczyk-Subotkowska ◽  
Witold Subotkowski ◽  
Ewa Gruszecka
Keyword(s):  
Isotope Effects ◽  
Heavy Atom ◽  
Transition States ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope

An MNDO SCF-MO study of proton transfer from fluoroethanols

1986 ◽  
Vol 64 (6) ◽  
pp. 1173-1178 ◽  
Author(s):  
Bo Anhede ◽  
Nils-Åke Bergman ◽  
A. Jerry Kresge
Keyword(s):  
Proton Transfer ◽  
Isotope Effects ◽  
Transition States ◽  
Kinetic Isotope Effects ◽  
Proton Exchange ◽  
Transfer Reactions ◽  
Correction Factors ◽  
Kinetic Isotope ◽  
Proton Transfer Reactions ◽  
Marcus Equation

Proton exchange between β-fluorinated ethanols and ethoxide ions has been studied using the MNDO SCF-MO method. Calculations were performed on reactions of ethoxide ion with ethanols substituted in the β-position with 0, 1, 2, and 3 fluorine atoms as well as on reactions where both the ethanol and the ethoxide ion were substituted with the same number (1, 2, 3) of fluorine atoms in the β-position. The energies obtained for the ion–molecule reactant complexes and the transition states from these reactions have been analyzed using the Marcus equation. Through the calculated force-constant matrices of reactants and transition states we also calculated the kinetic isotope effects for the proton-transfer reactions. The semiclassical isotopic rate constant ratios (kH/kD)s were found to be of rather normal magnitude and showed a variation with the energy of reaction. The calculated ratios of tunnel correction factors, QtH/QtD, proved to be unrealistically high. These factors were also calculated with the frequencies scaled down by 10% and this was found to reduce the QtH/QtD ratios to more realistic values.

Model Calculations of Isotope Effects. IV. Transition State Structures and the Question of Tunnelling in Proton Transfer Reactions

1979 ◽  
Vol 32 (9) ◽  
pp. 1883 ◽  
Author(s):  
DJ McLennan
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Normal Values ◽  
Isotope Effects ◽  
Transition States ◽  
Transfer Reactions ◽  
Model Calculations ◽  
Proton Transfer Reactions ◽  
Donor Acceptor ◽  
State Models

Model calculations of primary hydrogen isotope effects in proton transfer reactions are reported. The geometries and force fields of transition state models have been systematically varied with respect to both reactant-like and product-like character and to tight against loose character. The models include both hypothetical cut-off molecules and 2-nitropropane. Values of kH/kD greater than 17 are calculated for loose, symmetrical transition states in which the sum of the bond orders pertaining to the transferring proton is set at 0.6, and higher than normal values of (ED-EH) and ADIAH are also associated with such transition states. It is suggested that transition state looseness is a consequence of repulsive donor-acceptor steric interactions, and that several sets of experimental results which have hitherto been rationalized by the invocation of proton tunnelling may equally well be explained by postulating loose transition states.

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