Subject: Question concerning Spartan molecular modeling software

From: Gary Breton <[email-masked]>
Date: Fri, 23 Feb 2001 12:37:53 -0500

Hello folks,

I hope at least some of you have some experience with PC Spartan Pro.  I
recently purchased several copies of the software and began testing it with
some routine molecular mechanics (MMFF94) calculations.  Amazingly, when I
computed the energy of chlorocyclohexane with the Chlorine in the equatorial
position ( 1.4 kcal/mol) it was of HIGHER energy than when the Cl was axial
(1.1 kcal/mol).  This is contrary to experiment.  I ran the same calculation
utilizing CambridgeSoft's Chem3D, with Hyperchem (MM+), and MOLGEN (MM2) and
received the proper result (i.e., Cl prefers to be equatorial in the chair
conformation) and the calculated energy differences were consistent with the
experimental values.

Has anyone else observed this? is it a result of the force field? Am I doing
something wrong in Spartan that I am NOT doing in the other packages?  If it
is the force field, can I replace the parameters contained within Spartan?

Thanks for your help!

Gary W. Breton
Department of Chemistry
Berry College
PO Box 495016
Mount Berry, GA 30149