Subject: symmetry of transition states

From: [email-masked] (Joseph W. Bausch)
Date: Thu, 19 Jun 1997 01:58:50 -0500

I hope this question is meaningful and understandable.  I am curious about
the symmetry of a transition state connecting molecule A to an isomeric
structure B.  Are there any "rules" governing the symmetry of the
transition state as it relates to the symmetry of A and B?

For instance, say both A and B have C1 symmetry.  Must the transition state
have C1 symmetry, or can it have some higher symmetry group like Cs?

I'll summarize if there is sufficient interest.

JWB
--------

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From: "J. Sichel" <[email-masked]>
Date: Thu, 19 Jun 1997 16:43:23 -0300 (ADT)

> transition state as it relates to the symmetry of A and B?

Yes there are rules. Try the book by R.G.Pearson "Symmetry rules for 
chemical reactions" (Wiley 1976).

> have C1 symmetry, or can it have some higher symmetry group like Cs?

The transition state can have higher symmetry than either reactant or 
product. A simple example is the inversion of ammonia: reactant and 
product are C3v and the planar transition state is D3h. If you consider 
instead inversion of NHFCl, then reactant and product are C1 and the 
planar transition state is Cs as you have asked.

     John-M. Sichel
     Dept. de chimie et biochimie
     Universite de Moncton
     Moncton NB, Canada

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From: <[email-masked]>
Date: Thu, 19 Jun 1997 16:08:05 -0400 (EDT)

you may contact Professor Schaad, L. J in 
VANDERBILT UNIV,DEPT CHEM,BOX 1583/NASHVILLE//T/37235.
He has given several talks on the symmetry rules for
transition state. However, it seems that there is no formal
publication yet.

=================================================================
Dr. Buyong Ma             [email-masked]
Computational Center for Molecular Structure and Design
Department of Chemistry
University of Georgia
Athens, Georgia 30602 USA            Voice (706) 542-2044
=================================================================

On Thu, 19 Jun 1997, Joseph W. Bausch wrote:

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