From: Jacob Zabicky (zabicky$##$bgumail.bgu.ac.il)
Date: Tue Feb 19 2002 - 06:19:49 EST
Hello Richard,
As far as I understand it, the rate of reaction depends on the energy
difference between the ground and the transition states of the substrate,
assuming that the energy levels of the products are much lower (otherwise
complications with reversible reaction kinetics pop up). Therefore, the
relative thermodynamic stability of the different substrates is irrelevant.
BTW, what do you mean quantitatively by "thioesters are thermodynamically
unstable relative to oxygen esters"?
All the best,
Jacob
At 19:51 14/02/2002, Richard Feinman wrote:
>I don't know about questionable but mechanistic problems that I am interested
>in which I'm having a little trouble getting a grip on (although it may
>be elementary) are:
>
>1. It's usually assumed that although thioesters are thermodynamically
>unstable relative to oxygen esters, the rates of hydrolysis are similar.
> I wonder about the evidence for this. Fedor & Bruice studied trifluoroacetate
>esters and I wonder if this is representative.
>2. Along the same lines, it is also generally stated that thioesters
>are like ketones (due to poor electronegativity of S and limited
>delocalization).
> Is there comparative data on rates of hydrate formation of ketones relative
>to formation of tetrhedral intermediates in ester and thioester hydrolysis
>?
>
>--
>Richard Feinman
>rumford$##$onebox.com - email
>(718) 404-3901 x6280 - voicemail/fax
>
>
>
>---- "G. Robert Shelton" <rshelton$##$chem.ufl.edu> wrote:
>> orglist-ers,
>>
>> Just wanted to throw out a general question to the active people of
>> the list, and some of those not so active like myself who are waiting
>> for phyiscal organic question to be asked. And from there maybe start
>> some threads of conversation that would be of interest to some of us
>> that are not solely organic synthesis people. Hopefully this is the
>> place for this question. So In your opion, what are the most questionable
>> chemical mechanisms?
>>
>> -Robert
>>
>
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Prof. Jacob Zabicky
Institutes for Applied Research
Ben-Gurion University of the Negev Private: POB 12366, Beer-Sheva 84863
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