Re: ORGLIST: a question on stereochemical nomenclature

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From: Jonathan Brecher (jsb$##$
Date: Sun Jan 23 2005 - 21:48:18 EST

>Thank you. Sorry for insisting, but I am still missing something. Would
>not the chlorine atoms, as the heaviest of the the atoms attached to
>the asymmetric center, be the one determining the highest ranking
>group, in which case the cis priority rule will make for an S

I don't understand your question. Yes, the heaviest atoms would
determine the priority. That is Rule 1. In this case, the highest
priority substituent is the chlorine directly substitued to the
stereogenic carbon. The lowest priority is the hydrogen substituent.
Those are easy. That leaves the two substituents within the ring
itself (going towards the chloromethylenes on the left and right),
and those are constitutionally identical -- you can't differentiate
between them strictly by looking at the atomic numbers and their
connectivity. So rule 1 is not helpful. There are no isotopically
labeled atoms, so Rule 2 is not helpful either. That takes us to
Rule 3, which says that seqcis precedes seqtrans, and there *is* a
cis/trans difference, so that's all that's required.

Jonathan Brecher
CambridgeSoft Corporation
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