Subject: Summary of replies: resonance effect in O and S

From: Emad Tajkhorshid <[email-masked]>
Date: Wed, 17 May 2000 10:05:28 +0200 (MET DST)

Hi

This is a summary of the answers I got from CCL:

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Question:

> Hi
>
> I am looking for some references (experiment or calculations, text book,
> etc.) comparing the ability of O and S in sharing the lone pair with the
> pi-electronic system. As far as I remmeber, S was a weaker electron
> donating group (lower resonance effect), although its electronegativity is
> less. Any comment is welcome.
>
Emad

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From: Leticia Gonzalez Herrero <[email-masked]>
To: Emad Tajkhorshid <[email-masked]>
Subject: Re: CCL:resonance effect in O and S

Dear Emad, 
mabye this helps?
Gonzlez, L., M, O. and Yez, M. (1997): High level ab initio calculations
on the intramolecular hydrogen bond in
thiomalonaldehyde. J. Phys. Chem. 101, 9710-9719. 

thiomalonaldehyde contains both O and S with pi system,so we made some
discussion about your question. 

Good luck. 
Leticia
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  Dr. Leticia Gonzalez                      Tel: ()49 30 838 520 97
  Freie Universitaet Berlin                 Fax: ()49 30 838 547 92 
  Institut fuer Chemie                      Room: 35.17 
  Takustrasse 3                          [email-masked]         
  D-14195 Berlin        http://userpage.chemie.fu-berlin.de/~leti
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        If you find a solution and become attached to it,
        the solution may become your next problem.

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From: Yirong Mo <[email-masked]>
To: [email-masked]
Cc: [email-masked]
Subject: Re: CCL:resonance effect in O and S

Hi, Emad:

I did some calcualtions on 5-member rings and their corresponding
linear forms using recently developed block-localized wavefunction
(J.Chem.Phys.  109, 1687(1998) and JACS 121, 5737(1999)), however, the
manscript is still to be worked out.  In these calculations, I did
compare the resonance effect of O via S (also N via P etc).  For the
cyclic C4H4X, the vertical resonance energies for X=O and S are -35.8
and -31.0 kcal/mol, while for linear C4H6X, the resonance energies are
-14.8 and -9.2 kcal/mol with 6-31G(d).  Thus, We may conclude that S is
a slightly weaker electron donating group.  On the other hand,
Prof.Schleyer's NICS calculations give the data -13.6 and -13.9 ppm for
C4H4O and C4H4S, respectively, suggesting that O and S have similar
donating ability.

Hope this may help you a little.

Wishes, Yirong

Yirong Mo, PhD, Research Associate
Department of Chemistry
University of Minnesota

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From: Piotr Paneth <[email-masked]>
To: Emad Tajkhorshid <[email-masked]>
Subject: Re: CCL:resonance effect in O and S

Hi
look into papers of Perry Fry from mid 80'. I've been trying to calculate
=POS- using continuum solvent models and didn't see yet any level that
significantly differentiate charge distribution with the change of polarity
although Perry's and our own experimental results (isotope effects) suggest
that this should be so. Will be glad to see what responses you've got.
Cheers,
Piotr
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Professor Piotr Paneth
Department of Chemsitry, Technical University
Zeromskiego 116, 90-924 Lodz, Poland
fax/phone: (+48 42) 6313199  fax: (+48 42) 6365008

Thanx to everybody for replying.

Regards

Emad
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E. Tajkhorshid            http://genome.dkfz-heidelberg.de/users/emad
German Cancer Research Center; DKFZ      Email: [email-masked]
Dept. Molecular Biophysics (H0200)              Tel: +49 6221 42 2340
P.O.Box 101949,  69009 Heidelberg, Germany      FAX: +49 6221 42 2333
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