Subject: energies of conformations

From: Patrick Bultinck <[email-masked]>
Date: Tue, 10 May 1994 21:25:36 +0200 (MET DST)

Netters,

I probably have a bit strange question but anyway....

As probably everybody in the QC-field will aknowledge it is always useful 
to compare computed results with experiments.
I have been reading a number of articles now on theoretical calculations 
on a number of molecules. The different authors often refer to the same 
articles with experimental findings. It really strikes me when I find 
that one author claims that a relative energy X for a certain conformer 
compared to the energy of the global lowest energy conformation is too 
big to expect a certain occupation of the confomer, while another one 
sees it perfectly possible that given the energy difference X there would 
be a substantial occupation of the higher lying confomer!!!

My question is thus simple....

I would like to hear different opinions to how to more or less draw a 
line between confomers that may show an ***important*** occupation at a 
temperature T, and which conformers do not show any ***important*** 
occupation! I have thusfar found a number of quite contradictory 
statements, and would like to hear other peoples opinions.

Reactions may be sent directly to me or the CCl, anyway a summary will be 
posted some time next week...

Thanks a lot,

|-----------------------------------------------------------------------|
|     C-C                       Patrick Bultinck                        |
|    /   \                      Dept. Physical & Inorganic Chemistry    |
| C-O     O-C                   Section Quantum Chemistry               |
| |         |                   University of Ghent                     |
| C-O     O-C                   Krijgslaan 281 (S-3)                    |
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From: [email-masked] (Wilson_Bruce)
Date: Tue, 10 May 1994 16:58:10 -0400

> statements, and would like to hear other peoples opinions.
Sure, I'll wade in with a very equivocal answer:  "It depends!".  
Seriously.  If the Boltzman distribution shows a 1% population of
a conformer level, that may be insignificant for some applications, but
it may be highly significant for others.  But the simple answer is that
I'll do a Boltzman analysis, determine a relative population percentage
and then decide whether that's significant for the application at hand.
And I'll always report the energy difference, so that the reader can
decide whether that's significant or not.

		Bruce Wilson ([email-masked])