Subject: CCL: Examples of DG maxima where no PE maximum exists?

From: "Rzepa, Henry" <h.rzepa.-at-.imperial.ac.uk>
Date: Mon, 3 May 2004 09:19:19 +0100

In the temporary absence of a working search of the  CCL archives,
does anyone know of any examples of the following scenario?

The potential energy surface of a dissociative reaction may often
rise to the asymptotic maximum of infinite separation of the two
components. These two components will show a large increase in
the entropy,  and hence  any free energy increase for this process will be
substantially less than the potential energy increase. Depending 
on how the entropy evolves along the reaction path, its possible to imagine that 
unlike the potential energy, the free energy reaction path may
show a clear maximum (transition state) unmatched by one in the 
potential energy.

Does anyone know of any "classic" examples of such
entropy induced transition states? 
(its the sort of concept that eg a Scifinder search is difficult
to formulate for)
-- 

Henry Rzepa. Imperial College, Chemistry Dept.
+44 0778 626 8220 +44 020 7594 5804 (Fax)

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From: Per-Ola Norrby <pon)at(kemi.dtu.dk>
Date: Mon, 3 May 2004 17:45:43 +0200

>(its the sort of concept that eg a Scifinder search is difficult

	We published one a few years ago, for the Cu-catalyzed 
cyclopropanation: Chem. Eur. J. 2002, 8, 177-184.  This is a 
dangerous one to study: there are several publications based on 
ethylene, where you DO have a TS, but with any substituent, there is 
no TS on the PES, only on the free energy surface (and it's quite 
different from the one on the PES).

	Best regards,

	Per-Ola
-- 
Per-Ola Norrby, Assoc. Professor, http://organisk.kemi.dtu.dk/PON/
Technical University of Denmark, Department of Chemistry
Building 201, Kemitorvet, DK-2800 Kgs. Lyngby, Denmark
Email: pon)at(kemi.dtu.dk  tel +45-45252123,  fax +45-45933968

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From: Eugen Leitl <eugen_at_leitl.org>
Date: Mon, 3 May 2004 16:50:12 +0200

> does anyone know of any examples of the following scenario?

Google might be not completely up to date, but using site restriction might
work:

	http://www.google.com/search?q=site%3Accl.net&hl=en&num=100&btnG=Google+Search
 
-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a>
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