CCL:G: Resonance energy

To: "Pundlik, Savita Sunil " <savita.pundlik .. tcs.com>
From: "Sergio Manzetti sergio.manzetti]*[gmx.com"
Sent by: owner-chemistry+savita.pundlik==tcs.com .. ccl.net
Date: 10/04/2012 05:29PM
Subject: CCL:G: Resonance energy

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

Sergio

----- Original Message -----

From: Robert W. Gora robert.gora===pwr.wroc.pl

Sent: 10/04/12 10:01 AM

To: Manzetti, Sergio

Subject: CCL: Resonance energy

Dear Amy,
Dear All,

> Maybe my thinking is too simplistic. It seems like you could calculate the
> predicted value for the enthalpy of complete hydrogenation of your system
> which would be N times (N=# double bonds) that of one double bond). Then
> subtract the actual 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 propose to calculate constitutes the resonance
stabilization energy even though 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, What Is
Resonating?" [DOI 10.1021/ed083p223].

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

"The meaning of resonance energy as it appears in valence bond theory is the
lowering 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." Where the
term structure corresponds to "a single set of spin orbitals with a spin
coupling corresponding to a particular covalent or ionic bonding scheme."

Best,
Robert

PS. By the way, I apologize Brian Salter-Duke for forgetting to mention his
excellent code ;)

--
Robert W. Góra, Theoretical Chemistry Group, ICHFiT, WUT [http://zcht.info]
[http://www.researchgate.net/profile/Robert_Gora]
[http://www.researcherid.com/rid/B-3919-2010]