Subject: RE: Bonds vs No Bonds in Minimized Structures

From: "Robinson, James" <[email-masked]>
Date: Wed, 14 Nov 2001 12:29:48 -0000

Guassview merely add lines between two points in space. The question of
whether a bond is really there is not one to be addressed with the viewing
program. Perhaps bader bond-critical-point analysis may help answer the
bonding question. Does MP2 affect things? Keep an open mind, don't be fooled
by the pretty pictures alone.

J

-----Original Message-----
From: Gary Breton [mailto:[email-masked]]
Sent: Wednesday, November 14, 2001 12:17 PM
To: [email-masked]
Subject: CCL:Bonds vs No Bonds in Minimized Structures

Hello all,

I have been conducting some geometry minimizations on some
1,2-diazacyclobutane structures using Gaussian98 with the GaussView GUI.
When I minimize the parent compound (1,2-diazacyclobutane with N-H bonds) at
the RHF631G* level, everything looks fine.  If, however, I minimize at the
RB3LYP6311+G** level, a similar structure to the HF minimization results,
but GaussView does NOT SHOW a bond between the two nitrogen atoms.  The bond
has apparently not broken since the molecule adopts a geometry as if its
still there (i.e., in the HF minimization the N-N, C-N and C-C bond lengths
are 1.45405, 1.47272 and 1.53174, respectively, while in the B3LYP they are
1.49052, 1.49351 and 1.53844, respectively).  Furthermore, if I start with
the HF structure and further minimize at the B3LYP level, the bond again
disappears!  If I start with the B3LYP structure and ADD a N-N bond and then
re-minimize, it again eliminates the bond.

Is there any significance to the presence or absence of the bond?  Why would
GaussView not put a bond into the structure?

Thanks and best regards!

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

"There's a light at the
end of the tunnel, but it
may be an oncoming train"

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From: "Shobe, Dave" <[email-masked]>
Date: Wed, 14 Nov 2001 09:38:12 -0500

I would not consider Gaussview's display or non-display of a bond as having
ANY significance.  I think there is a distance cutoff below which the two
atoms are considered to be "bonded", probably based on covalent radii or
something like that.

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

Don't bother flaming me: I'm behind a firewall.

-----Original Message-----
From: Gary Breton [mailto:[email-masked]]
Sent: Wednesday, November 14, 2001 7:17 AM
To: [email-masked]
Subject: CCL:Bonds vs No Bonds in Minimized Structures

Hello all,

Thanks and best regards!

Gary W. Breton

"There's a light at the