Subject: MOPAC for choosing reaxn mechs?

From: "Hr Dr. S. Shapiro" <[email-masked]>
Date: Mon, 5 Dec 1994 15:58:04 +0100 (MET)

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: [email-masked]
FAX-nr: ( ... + 1) 261'56'83