From owner-chemistry@ccl.net Fri Oct 5 09:11:00 2012 From: "Savita Pundlik savita.pundlik!^!tcs.com" To: CCL Subject: CCL:G: Resonance energy Message-Id: <-47725-121004232004-9563-zjW5eGd/7SBBmEIsJtBDqQ(-)server.ccl.net> X-Original-From: Savita Pundlik Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="iso-8859-1" Date: Fri, 5 Oct 2012 08:49:51 +0530 MIME-Version: 1.0 Sent to CCL by: Savita Pundlik [savita.pundlik*tcs.com] Hello,

Years ago we had assessed structural characteris= tics in some fused ring systems using topographical analysis of electron de= nsity and electrostatic potential (JACS 1995, 117, 9559).
We found that = the charge pulling and pushing effects are reflected in e.g. the density at= bond critical points.
Calculation of this needs some post processing af= ter SCF.
Can these quantities serve your purpose?

Thanks and best= wishes,

Savita Pundlik
Tata Consultancy Services
Mailto: savi= ta.pundlik .. tcs.com
Website: http://www.tcs.com
______________________= ______________________
Experience certainty. IT Services
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-----owner-chemistry+savita.pundlik= =3D=3Dtcs.com .. ccl.net wrote: -----
To: "Pundlik, Savita Sunil " <savita.pundlik .. tcs.c= om>
From: "Sergio Manzetti sergio.manzetti]*[gmx.com"
Sent by: owner-chemistry+savita.pundlik=3D=3Dtcs.com .. ccl.net<= br>Date: 10/04/2012 05:29PM
Subject: CCL:G: Resonance energy

Robert, I ag= ree on that Truhlar (and Friedman) are central references on this. However,= how can a program (like Gaussian for isntance) be used to apply their mode= l for resonance?
= Amy's suggestion is quite interesting, and could be a way to get a glance o= f resonance for certain non-modifed PAHs for instance.
=
= Sergio
=
=

=  

=
=

= ----- = Original Message -----

=

= From: = Robert W. Gora robert.gora=3D=3D=3Dpwr.wroc.pl

=

= Sent: = 10/04/12 10:01 AM

=

= To: Ma= nzetti, Sergio

=

= Subjec= t: CCL: Resonance energy

=
=
=
=  
Dear A= my,
Dear All,

> Maybe my thinking is too simplistic. It seem= s like you could calculate the
> predicted value for the enthalpy of= complete hydrogenation of your system
> which would be N times (N= =3D# double bonds) that of one double bond). Then
> subtract the act= ual predicted value for the complete hydrogenation (which
> will be = less due to the resonance stabilization). That difference should be
>= ; the resonance energy of the system.

I don't think what you propos= e to calculate constitutes the resonance
stabilization energy even thou= gh the enthalpy of hydrogenation is obviously
somehow related.

= Apart from the recent paper by Rashid et al. I have mentioned previously, I=
could recommend a discussion in the Journal of Chemical Education that=
originated from Robert C. Kerber's paper "If It’s Resonance, Wha= t Is
Resonating?" [DOI 10.1021/ed083p223].

Personally, I am par= ticularly fond of Donald G. Truhlar's reply "The Concept
of Resonance" = ibid [DOI 10.1021/ed084p781], which captures the essence of
resonance a= s it is understood in the quantum chemistry community:

"The meaning= of resonance energy as it appears in valence bond theory is the
loweri= ng of the calculated ground state electronic energy when one improves a quantum mechanical model containing a single valence bond structure in the=
wave function to include other significant valence bond structures." W= here the
term structure corresponds to "a single set of spin orbitals w= ith a spin
coupling corresponding to a particular covalent or ionic bon= ding scheme."

Best,
Robert

PS. By the way, I apologize = Brian Salter-Duke for forgetting to mention his
excellent code ;)
<= br>--
Robert W. G=F3ra, Theoretical Chemistry Group, ICHFiT, WUT [http:= //zcht.info]
[http://www.researchgate.net/profile/Robert_Gora]
[htt= p://www.researcherid.com/rid/B-3919-2010] =
=
=
=

=  

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