Reaction mechanism and isotope effects derived from centroid transition state theory in intramolecular proton transfer reactions

2001 ◽  
Vol 115 (13) ◽  
pp. 5891-5902 ◽  
Author(s):  
Radu Iftimie ◽  
Jeremy Schofield
Keyword(s):  
Reaction Mechanism ◽  
Proton Transfer ◽  
Transition State ◽  
Transition State Theory ◽  
Isotope Effects ◽  
Intramolecular Proton Transfer ◽  
State Theory ◽  
Transfer Reactions ◽  
Proton Transfer Reactions

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.

A MODEL FOR THE HYDROGEN BOND AND PROTON TRANSFER REACTIONS

1964 ◽  
Vol 42 (8) ◽  
pp. 1822-1834 ◽  
Author(s):  
R. F. W. Bader
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Transfer Reactions ◽  
Simple Extension ◽  
Kinetic Isotope ◽  
Proton Transfer Reactions ◽  
Hydrogen Deuterium ◽  
Base Strength

A simple extension of Platt's model for determining the force constants in diatomic hydrides is used to investigate the properties of transition states for proton transfer reactions. The model is first tested by comparing the predicted and observed changes in bond lengths and stretching and bending frequencies for [Formula: see text] systems. The quantities predicted for the transition state are the geometry and the perpendicular bending frequencies. The implications of the results with regard to the interpretation of hydrogen–deuterium kinetic isotope effects are discussed. In particular, the variations in both the isotope effect and the geometry of the transition state with changing acid or base strength are considered in detail.

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