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How to determine whether the face of the attached alkene is re or si? If assigning priorities in regard to the left C atom it is re, but for the right C atom it is si. How is it actually determined? enter image description here

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I’m pretty sure that this depends on the atom attacked. Most attacks on double bond are stepwise to a certain extent. And even when they aren’t, the absolute configuration should be discussed on a per-atom basis.

But if you have a concerted reaction and want to label both: (2si,3re).

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  • $\begingroup$ Is there any other way to label them? If the alkyl chains are too complex, it isn't easy to determine the locants of these C atoms (like 2 and 3 in the given example). $\endgroup$ – RBW Aug 21 '16 at 15:55
  • $\begingroup$ Not that I know of =C @Marko. $\endgroup$ – Jan Aug 21 '16 at 15:59
  • $\begingroup$ So it is obligatory to know the name of the compound with all the locants to be able to name the face properly. $\endgroup$ – RBW Aug 21 '16 at 17:01

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