CCL:G: Ring pseudorotation

Hallo Alcides
 
Unfortunately, there is no "auto" way, and magic is an illusion, at least so I am told.
 
I would either generate starting conformations using Cremer and Pople's formula for the deviation from the mean ring plane, or the empirical formula for the torsion angles by Geise and Altona. After that, you are at the mercy of the Gaussian minimiser.
 
However, I have found the latter to be very efficient in going to transition states. If you are interested in energy profiles of the pseudorotation, do IRCs once you have the energy maxima. Your energy surface will probably be very flat, so Gaussian may (will) have troubles with the (automatic) IRCs. You propably will have to distort the transition state in the direction of the proper eigenvector and do a downhill IRC, and even that is not guaranteed to work.
 
May the force be with you.
 
Jan

From: owner-chemistry+jlmd==sun.ac.za]^[ccl.net [mailto:owner-chemistry+jlmd==sun.ac.za]^[ccl.net] On Behalf Of Alcides Simao alsimao^^^gmail.com
Sent: 08 March 2012 13:49
To: Dillen, Jan <jlmd]^[sun.ac.za>
Subject: CCL:G: Ring pseudorotation

Hello all!

I'm trying to study a pseudorotation of a substituted pyrrolidine ring using GAUSSIAN 03. Although literature exists on the theme, I haven't come across any input example of it,so I'm trying to compute it in a way that I dislike particulary, which is to set a plane made of four atoms, and set one of the atoms off-plane, which is quite unrealistic. I would ask if anyone could kindly tell me what is your way of computing pseudorotation, and if you happen to have an 'automagic' way of doing so, if you would be so kind as to share it.

Best,

Alcides

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