CCL: Case Studies of QM Computational Chemistry in Reactivity
- From: Jean-Pierre DJUKIC <djukic()unistra.fr>
- Subject: CCL: Case Studies of QM Computational Chemistry in
- Date: Fri, 11 Sep 2015 10:08:06 +0200
Sent to CCL by: Jean-Pierre DJUKIC [djukic^_^unistra.fr]
Tom is right.
I wonder how this very example that Tom quotes would be treated with
modern DFT methods. The rotational barrier of Cr(CO)3 is in
benzene[Cr(CO)3] around 1 kcal/mol. In substitued systems, say
anilineCr(CO)3 it rises a bit for various reasons, but not that much
nonetheless there exist rotamers of very close energy the statistical
weight of which is thought to be different for each rotamer. This
statistical distribution is indeed temperature dependent, it explains
why a nucleophile will prefer attacking at the meta position relative
some nucleofuge and not ortho like intuition could suggest at a first
glance under "some" conditions.
We are talking about kinetic discrimination of states close in energy.
The same stands for enantioselective processes where the differences of
TS energies may challenge common accuracy in DFT, then add solvation
issues ... and the fact that in reality molecules are animated and
flexible indeed and not static like we generally see them in most
Le 10/09/2015 18:58, Tom Albright talbright1234-$-gmail.com a écrit :
Furthermore the orientation of the Cr(CO)3 group directs attack by
nucleophiles on the arene. All this at the (almost, but I am sure in
your mind, totally) unreliable EHT level. The energy differences are
small but one can formulate a coherent explanation of the
regioselectivity. This is useful.
Dr Jean-Pierre DJUKIC (Đukić)(DR CNRS)
Laboratoire de Chimie et Systémique OrganoMétalliques (LCSOM)
LCSOM, Institut de Chimie de Strasbourg
UMR 7177 CNRS / Université de Strasbourg
4, rue Blaise Pascal
67000 Strasbourg Cedex.
me joindre: Institut Le bel, aile nord, 9ème étage,
pièce 942b, tel: +33
Conseil Scientifique de l'Institut de Chimie du CNRS