From owner-chemistry@ccl.net Sat Aug 30 01:58:01 2008 From: "Arindam Ganguly arindamganguly.:.gmail.com" To: CCL Subject: CCL: tautomerism software Message-Id: <-37682-080829163859-25174-SPXJaZBVzN1XrLttnsi47w|,|server.ccl.net> X-Original-From: "Arindam Ganguly" Content-Type: multipart/alternative; boundary="----=_Part_19248_10492042.1220034875794" Date: Fri, 29 Aug 2008 13:34:35 -0500 MIME-Version: 1.0 Sent to CCL by: "Arindam Ganguly" [arindamganguly:+:gmail.com] ------=_Part_19248_10492042.1220034875794 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline Dear CCL users, Thanks very much for providing prompt response to my question. However,i do apologise for not being specific about my question. I agree with Bob, yes those are two questions i am trying to answer. If any tautomers exist for a particular structure and their relative stabilities, consequently their room temperature concentrations. Thanks again. arindam On Thu, Aug 28, 2008 at 5:57 PM, David Gallagher gallagher.da-*-gmail.com < owner-chemistry+*+ccl.net> wrote: > > Sent to CCL by: David Gallagher [gallagher.da]=[gmail.com] > Hi Bob, > > It seems that you may be unaware that quantum chemistry methods, already > proposed by myself and some others, provide the necessary thermodynamic and > kinetic information to establish both the equilibrium ratio of the different > tautomers and their speed of interconversion at a particular temperature. > > It is quite simple to perform a free energy calculation on each tautomer > with almost any quantum chemistry package to estimate the free energies > (thermodynamics), either gas phase or in an appropriate solvent field. The > ratio of the tautomers can then be determined via a Boltzmann distribution. > > The speed of interconversion (kinetics) can be established from the height > of the energy barrier to interconversion (activation energy) and the > Arrhenius equation. The height of the energy barrier is simply the free > energy of the transition state (between the tautomers) minus the free energy > of the appropriate tautomer. Although, more involved than ground state > calculations, characterizing transition states in most cases is relatively > straightforward for some quantum chemistry packages (further details on > reaction modelling are posted at > http://cacheresearch.com/presentations.html ) > > Far from being 'not relevant for most purposes', the enol tautomer can be > the most abundant for some simple ketones such as acetyl-acetone, and even > in very low concentrations when the keto-form prevails, the enol tautomer > may still be responsible for certain characteristics of a molecules > chemistry or reactivity. > > Regards, > David > > > > At 07:22 AM 8/28/2008, Bob Clark bclark-x-bcmetrics.com wrote: > > The responders so far have failed to distinguish between two kinds of >> questions: "Could the molecule possibly tautomerize - i.e., do tautomeric >> structures exist?" (which is what you actually asked) and "Will the >> molecule tautomerize?" Enumerating all possible tautomers is pretty >> straightforward, but identifying relevant tautomers is often very hard. >> Hence the second question is a lot harder to answer, because one has to >> take kinetic as well as thermodynamic considerations into account. The enol >> tautomer of most simple ketones, for example, isn't relevant for most >> purposes, and there are steroid CH tautomers that are perfectly happy to sit >> in separate bottles on the shelf for years. >> >> So please provide some context: what do you want to use the information >> for? >> Good luck, >> Bob C. >> >> Sent to CCL by: "Arindam Ganguly" [arindamganguly|gmail.com] >>> Dear CCL users, >>> Is there any software out there which can predict the possibility of >>> tautomerism being present in a molecule. Any suggestions and pointers will >>> be really helpful. Thanks in advance. >>> >>> Arindamhttp://www.ccl.net/chemistry/sub_unsub.shtmlConferences: > http://server.ccl.net/chemistry/announcements/conferences/> > > -- Arindam Ganguly Graduate Student VP(Chemistry Graduate Student Association-CGSA) Dept. of Chemistry, UMKC Phone:-816-419-1806 Email:- ArindamGanguly+*+gmail.com ------=_Part_19248_10492042.1220034875794 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline
Dear CCL users,
Thanks very much for providing prompt response to my question. However,i do apologise for not being specific about my question. I agree with Bob, yes those are two questions i am trying to answer. If any tautomers exist for a particular structure and their relative stabilities, consequently their room temperature concentrations. Thanks again.
arindam

On Thu, Aug 28, 2008 at 5:57 PM, David Gallagher gallagher.da-*-gmail.com <owner-chemistry+*+ccl.net> wrote:

Sent to CCL by: David Gallagher [gallagher.da]=[gmail.com]
Hi Bob,

It seems that you may be unaware that quantum chemistry methods, already proposed by myself and some others, provide the necessary thermodynamic and kinetic information to establish both the equilibrium ratio of the different tautomers and their speed of interconversion at a particular temperature.

It is quite simple to perform a free energy calculation on each tautomer with almost any quantum chemistry package to estimate the free energies (thermodynamics), either gas phase or in an appropriate solvent field.  The ratio of the tautomers can then be determined via a Boltzmann distribution.

The speed of interconversion (kinetics) can be established from the height of the energy barrier to interconversion (activation energy) and the Arrhenius equation.  The height of the energy barrier is simply the free energy of the transition state (between the tautomers) minus the free energy of the appropriate tautomer.  Although, more involved than ground state calculations, characterizing transition states in most cases is relatively straightforward for some quantum chemistry packages (further details on reaction modelling are posted at http://cacheresearch.com/presentations.html )

Far from being 'not relevant for most purposes', the enol tautomer can be the most abundant for some simple ketones such as acetyl-acetone, and even in very low concentrations when the keto-form prevails, the enol tautomer may still be responsible for certain characteristics of a molecules chemistry or reactivity.

Regards,
David



At 07:22 AM 8/28/2008, Bob Clark bclark-x-bcmetrics.com wrote:

The responders so far have failed to distinguish between two kinds of questions: "Could the molecule possibly tautomerize - i.e., do tautomeric structures exist?" (which is what you actually asked)  and "Will the molecule tautomerize?"  Enumerating all possible tautomers is pretty straightforward, but identifying relevant tautomers is often very hard.  Hence the second question is a lot harder to answer, because one has to take kinetic as well as thermodynamic considerations into account.  The enol tautomer of most simple ketones, for example, isn't relevant for most purposes, and there are steroid CH tautomers that are perfectly happy to sit in separate bottles on the shelf for years.

So please provide some context: what do you want to use the information for?
Good luck,
Bob C.

Sent to CCL by: "Arindam  Ganguly" [arindamganguly|gmail.com]
Dear CCL users,
Is there any software out there which can predict the possibility of tautomerism being present in a molecule. Any suggestions and pointers will be really helpful. Thanks in advance.

Arindam







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--
Arindam Ganguly
Graduate Student
VP(Chemistry Graduate Student Association-CGSA)
Dept. of Chemistry, UMKC
Phone:-816-419-1806
Email:- ArindamGanguly+*+gmail.com
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