Im agree with you but if you consider triphenylphosphorane such as
ethoxycarbonylmethylene triphenylphosphorane you will have different
equilibrium between the cis and trans form function of the organic solvent. If
you increase the polarity of the solvent, the equilibrium shifts in the
direction of the trans isomer.
To explain this equilibrium if you take the cis rotamer the P+/O- attraction is
maximised. So, Increasing the relative permittivity of the solvent, there will
be reduction in the attraction of the opposite charges, thus the trans form
will increase respect to the cis. To explain into images:
So.. probably i was too generic but i wanted to talk about situations like this.
Of course the simple triphenilphosphorane have no isomerism, but Jean-Marc do
you have any other example about cis/trans configuration?
Have a nice weekend
Marco
> On 11 Mar 2016, at 18:44, Jean-Marc Nuzillard <jm.nuzill...@univ-reims.fr>
> wrote:
>
> Le 11/03/2016 10:38, Giuseppe Marco Randazzo a écrit :
>> An example can be the case of this isomerism is given by
>> triphenylphosphorane (Witting reagents).
>
> Wittig reagents with their three identical phenyl groups on the phosphorus
> atom
> do not present any intriguing configuration problem around the P=C bond,
> contrarily to the compound that it was about in Greg's first message on this
> topic.
>
> I also wanted to point out that chirality is not necessarily centered on an
> atom
> but may be axial, like in allenes:
> https://en.wikipedia.org/wiki/Axial_chirality
> <https://en.wikipedia.org/wiki/Axial_chirality>
>
> All the best,
>
> Jean-Marc
>
>>
>> Here i give to you some publications were can find a clear publication about
>> cis/trans isomerism and the importance.
>>
>> [1] Conformation isomerism and coupling constants of formylmethylene
>> triphenylphosphorane (C6H5)3P=CH-CHO
>> Comptes Rendus des Seances de l'Academie des Sciences, Serie C: Sciences
>> Chimiques (1970), 270, (21), 1747-9.
>>
>> [2] Structural and conformational analysis of 2-triphenylphosphoranylidene
>> succinic acid derivatives by 1H, 13C and 31P one and two dimensional NMR
>> spectroscopy and molecular modelling
>> Radu Bacaloglu, Andrei Blaskó, Clifford A. Bunton, Giorgio Cerichelli,
>> Fernando Castaneda and Enrique Rivera
>> J. Chem. Soc., Perkin Trans. 2, 1995, 965-972
>> DOI: 10.1039/P29950000965
>>
>>
>> [3] Favoured conformations of methyl isopropyl, ethyl isopropyl, methyl
>> tert-butyl, and ethyl tert-butyl 2-(triphenylphosphoranylidene)malonate
>>
>> [4] Conformations of diester triphenylphosphonium ylides with an ylidic
>> ester or keto and ester ylidic groups
>>
>>
>> Best regards
>> Marco
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>> On 11 Mar 2016, at 10:12, Greg Landrum <greg.land...@gmail.com
>>> <mailto:greg.land...@gmail.com>> wrote:
>>>
>>>
>>> On Fri, Mar 11, 2016 at 10:05 AM, Jean-Marc Nuzillard
>>> <jm.nuzill...@univ-reims.fr <mailto:jm.nuzill...@univ-reims.fr>>wrote:
>>>
>>> Le 11/03/2016 05:11, Greg Landrum a écrit :
>>>>
>>>> Here's a question for the chemists in the group: do we need to be
>>>> concerned about representing the stereochemistry of the P=C bond in
>>>> substructures like O=P(/O)=C/C under normal circumstances?
>>>
>>> It has a meaning to write that the configuration of the P=C bond is Z or E.
>>>
>>> If this is the case, I'd love to add some real examples to the test suite.
>>> Can you point me to some examples (or a paper/web page talking about the
>>> topic)?
>>>
>>> -greg
>>>
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>>
>
>
> --
> Jean-Marc Nuzillard
> Institut de Chimie Moléculaire de Reims
> CNRS UMR 7312
> Moulin de la Housse
> CPCBAI, Bâtiment 18
> BP 1039
> 51687 REIMS Cedex 2
> France
>
> Tel : 03 26 91 82 10
> Fax : 03 26 91 31 66
> http://www.univ-reims.fr/ICMR <http://www.univ-reims.fr/ICMR>
>
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