Subject: Modeling a chemical reactivity

From: may abdelghani <may01dz _()_ yahoo.fr>
Date: Thu, 23 Jun 2005 12:17:54 +0200 (CEST)

Hello, CCLers

Can, some body tell me how I can model this reaction: A+ B \\\\.>C (not, A\\\\\ >B, I know how I do), with computational chemistry software, like spartan, hyperchem, G98/03 ext
Best regards

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From: "Phil Hultin" <hultin _+_ cc.umanitoba.ca>
Date: Thu, 23 Jun 2005 13:27:05 -0500

Modeling a bimolecular reaction is not all that different from doing a
unimolecular process.  It is a little harder to come up with a good
transition structure, but if you have some hypothesis for what that TS might
look like, you can start there.

1)       Obtain optimized geometries and frequencies for starting compounds
and product(s) at the desired level of theory.

2)       It is not so easy to use TS searching methods like QST2 and QST3
(in Gaussian) for bimolecular processes, because of the uncertainty as to
what "starting" and "ending" states should look like.  If the reaction is
simple enough, you can use these methods though, just imagine what you think
the system might look like immediately before and immediately after a
reaction event, manually create these states from your optimized structures,
and run the TS search.  No promises - this does not always work, but as I
said if the reaction is fairly simple (like the SN2 reactions we studied) it
is a good start.

3)       If you can't get a decent TS from an automated search, then use
"chemical intuition" to create your best guess and use opt=(TS) to minimize
to a 1st order saddle point.

Dr. Philip G. Hultin

Associate Professor of Chemistry,

University of Manitoba

Winnipeg, MB

R3T 2N2

hultin _+_ cc.umanitoba.ca

http://umanitoba.ca/chemistry/people/hultin

  _____  

From: Computational Chemistry List [mailto:chemistry-request _+_ ccl.net] On
Behalf Of may abdelghani
Sent: June 23, 2005 5:18 AM
To: chemistry _+_ ccl.net
Subject: CCL:Modeling a chemical reactivity

Hello, CCLers  <http://us.i1.yimg.com/us.yimg.com/i/mesg/tsmileys2/33.gif> 

Can, some body tell me how I can model this reaction: A+ B\\\\.>C (not,
A\\\\\ >B, I know how I do), with computational chemistry software, like
spartan, hyperchem, G98/03 ext

Best regards

  _____  

Appel audio GRATUIT partout dans le monde avec le nouveau Yahoo! Messenger
Tilichargez
<http://us.rd.yahoo.com/messenger/mail_taglines/default/*http:/fr.messenger.
yahoo.com>  le ici !