Subject: RE: Aromaticity, pi and sigma?

From: "Shobe, Dave" <[email-masked]>
Date: Thu, 14 Sep 2000 16:26:03 -0400

This may or may not be the one you're looking for, but here goes:

Sason S. Shaik; Philippe C. Hiberty
When Does Electronic Delocalization Become a Driving Force of Molecular
Shape and Stability? The "Aromatic" Sextet 
J.Amer.Chem.Soc. 1985, 107 : 11 3089-3095.

The argument isn't really that the "aromaticity" is in the sigma system, but
that the sigma system is what allows an aromatic ground state (instead of a
transition state like that of the Cope rearrangement).  Benzene is stable
and a regular hexagon because it meets *two* criteria, a sigma system that
favors equal bond lengths, and a pi system that doesn't penalize equality of
bond lengths greatly.

--David Shobe
Süd-Chemie Inc.
phone (502) 634-7409
fax     (502) 634-7724
email  [email-masked]

Any opinions herein are not necessarily representative of Süd-Chemie.

-----Original Message-----
From: Jens Spanget-Larsen [mailto:[email-masked]]
Sent: Thursday, September 14, 2000 6:42 AM
To: [email-masked]
Subject: CCL:Aromaticity, pi and sigma?

Dear CCL:

I saw some time ago a paper with a theoretical analysis of the origin of 
"aromaticity" in benzene (and possibly other species), concluding that the 
so-called aromatic stability originated from the sigma-system rather than
the 
pi-system.  However, I cannot trace the original reference.  Anybody knows
it?  
Have additional work been published in this field?

Yours, Jens >--< 
                             
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