[cseil]

Hi,
i'm studying the Ziegler-Natta catalysis and I cannot understand this image.



Can you explain me how to calculate which one is re and which one is si?
I know that I have to calculate the priorities, but I just cannot understand WHAT priorities (which atoms?)

Thank you

[pgk]

Firstly, you need to understand the Cahn-Ingold-Prelog rules.
Question: Which functional group has the highest molar mass, the metal, the methyl or the inserted one?
Hint1: According to the Cahn-Ingold-Prelog rules, priority works by decreasing the molar mass of the substituents, in a clockwise order (directed to the right side) when looking towards the optical asymmetric center, after the reaction.
Hint2: In case of isotopes, priority is based on the atomic number.

[pgk]

The slight difference between the ρ-,σ- (or else, r-,s-) and the R-,S- designation in the Cahn-Ingold-Prelog nomenclature system,  is that the ρ-,σ- (or else, r-,s-) designation refers to the atom with highest mass (or even better, highest atomic number) of the bonded group; while the R-,S- designation refers to the atom with the highest mass (or even better, highest atomic number) that is bonded with the assymetric carbon (or the assymetric heteroatom). But ignore it for the moment, because generally, both designations lead to the same nomenclature result.

[orgopete]

Because of how the structures have been drawn, I cannot tell what is meant. None the less, the top face of the left structure of proponents is the "re" face, see http://en.wikipedia.org/wiki/Prochirality.

[cseil]

Firstly, you need to understand the Cahn-Ingold-Prelog rules.
Question: Which functional group has the highest molar mass, the metal, the methyl or the inserted one?
Hint1: According to the Cahn-Ingold-Prelog rules, priority works by decreasing the molar mass of the substituents, in a clockwise order (directed to the right side) when looking towards the optical asymmetric center, after the reaction.
Hint2: In case of isotopes, priority is based on the atomic number.

But do I have to consider the metal also?
Because the -CH2 is the one bonded with the asymmetrical CH, not the metal.

You can see what I mean here:
https://en.wikipedia.org/wiki/Cossee%E2%80%93Arlman_mechanism

[pgk]

The metal is not consiidered in the prochirality nomenclature (But it is considered in the nomenclature of the organometallic compound}.

[orgopete]

Because of how the structures have been drawn, I cannot tell what is meant. None the less, the top face of the left structure of proponents is the "re" face, see http://en.wikipedia.org/wiki/Prochirality.

"propene"