MOPAC for choosing reaxn mechs?



 Dear Colleagues;
      I am interested in a particular substitution reaction
                           AX + Y -> AY + X
 It is likely that this reaction proceeds predominantly by either of two
 routes:
 a classical Sn2 Walden-type inversion reaction
                  Y-  +  AX  ->  [Y-A-X]-  ->  AY  +  X-
 or via a single electron transfer type of substitution reaction
                          AX  +  Y-  ->  AX.-  +  Y.
                        AX.-  +  Y.  ->  A.  +  X:-
                          A.  +  Y.  ->  AY
 >From the nature of the reactants and products, it seems likely that the re-
 action involves free radicals.  HOWEVER, my question is:
      Is there a way of deciding which of the above two postulated mechanisms
 is _most likely_ to predominate using MOPAC 6.0?  Are there components of the
 output from a MOPAC run that enable you to decide whether the reaction likely
 proceeds as a single electron transfer reaction or as a Walden inversion?  I
 am able to draw Z-matrices for the reactant, product, and all of the postu-
 lated mechanistic intermediates.
      I would ask people who are knowledgable about using MOPAC for studying
 paths or mechanisms of chemical reactions to kindly contact me on the above
 matter and to advise me how to proceed.  Specifics (e.g., keywords, useful
 components of the MOPAC output) would be most sincerely appreciated, as would
 relevant literature references.
      I thank all responders for generously sharing their information with me.
 Yours respectfully,
 (Dr.) S. Shapiro
 Institut fuer orale Mikrobiologie und allgemeine Immunologie
 Zentrum fuer Zahn-, Mund-, und Kieferheilkunde der Universitaet Zuerich
 Plattenstrasse 11
 Postfach
 CH-8028 Zuerich, Switzerland
 Internet: toukie at.at zui.unizh.ch
 FAX-nr: ( ... + 1) 261'56'83