Subject: CCL:transition-state energies

From: David Gallagher <dgallagher/at/cachesoftware.com>
Date: Wed, 09 Jun 2004 06:37:56 -0700

Hi Joe,

The critical number you would need is the activation energy, i.e. the 
difference between the transition state energy and the reactants ground 
state energy (ideally free energies including the entropic term). This 
should correlate with the energy of activation (Ea) from the Arrhenius 
equation.

Then, you would need to test the correlation of the calculated activation 
energies with some experimentally-derived numbers to:
1) establish that the model and theory-level does reasonably reproduce your 
experimentally observed results
2) to create a 'calibration' equation to more accurately estimate 
activation energies for new reaction paths

If kinetically controlled, then the product ratios should be related to the 
respective reaction rates. If thermodynamically controlled, then the 
product energies (energies of reaction) should control the product ratios.

This approach has been applied in a paper by: Malwitz, N., Reaction Kinetic 
Modeling from PM3 Transition State Calculations, J. Phys. Chem., Vol 99, 
No. 15, 1995 p. 5291

Regards,
David Gallagher
CAChe Group, Fujitsu
Portland, Oregon

At 11:10 AM 6/8/2004, Joe Harriman wrote:
>Hello everyone,
>
>I have some transition-sate structures and their corresponding 
>energies.  In addition, I
>have the enantiomeric excess values for the products that arise from these
>transition-state structures.  Is there a method that can be used to 
>correlate in silico
>transition-state energies to the ee's reported in litterature.  I have 
>been searching
>in vain for a method, but have been unsuccesful to date.  Any help would 
>be greatly
>appreciated.
>
>Thank you,
>
>Joe
>----------------------------------
>Joe Harriman
>Computational Chemistry
>University of New Brunswick
>Room 228
>Toole Hall
>s808o/at/unb.ca
>476-6543
>----------------------------------