Subject: Fwd: CCL:transition-state energies

From: arashid<<at>>iqe.phys.ethz.ch
Date: Thu, 24 Jun 2004 06:14:47 +0000

Forwarded Message:
> To: Joe Harriman <s808o<<at>>unb.ca>
> From: Per-Ola Norrby <pon<<at>>kemi.dtu.dk>
> Subject: CCL:transition-state energies
> Date: Wed, 9 Jun 2004 08:30:16 +0200
> -----
<pre>
>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.

	This comes out of the Eyring or Arrhenius equations, which 
you find in any basic physical chemistry text book.  Arrhenius: k = A 
exp(-Ea/RT); I prefer Eyring, but they give the same results when 
you're looking at relative rates.  As a first approximation assume 
that the constant(s) are equal for both paths (usually including the 
entropy, a fairly strong approximation...).  I assume that you're 
looking at an irreversible step, then the ratio of products, r, can 
be obtained simply as the ratio of rate constants, r = exp(DEa/RT), 
where DEa is the difference in transition state energy (all the 
constants disappear in the division).  When you have the ratio, the 
ee is easily obtained from ee = (r-1)/(r+1), which is the excess 
divided by the total, the definition of ee.

	/Per-Ola
-- 
Per-Ola Norrby, Assoc. Professor, <a 
href="http://organisk.kemi.dtu.dk/PON/">http://organisk.kemi.dtu.dk/PON/</a>
Technical University of Denmark, Department of Chemistry
Building 201, Kemitorvet, DK-2800 Kgs. Lyngby, Denmark
Email: pon<<at>>kemi.dtu.dk  tel +45-45252123,  fax +45-45933968

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