I need to think more about it tomorrow, I think your logic is correct but I
wouldn't say it's critically important. You're conflating two procedures - a)
finding stereochemistry vs b) naming it. You only need CIP for b, a is more
efficiently and correctly handled with group theory.
"Everything looks like a nail to a man with a hammer"
- John
> On 15 May 2017, at 23:47, Robert Hanson <hans...@stolaf.edu> wrote:
>
> I'm interested in two things. First, feedback on a proposed amendment to CIP
> Rule 1b. Second, suggestions for how to officially propose this.
>
> Current Rule 1:
>
> (1a) higher atomic number precedes lower;
> (1b) a duplicate atom node whose corresponding nonduplicated atom node is the
> root or closer to the root ranks higher than a duplicate atom node whose
> corresponding nonduplicated atom node is farther from the root.
>
> Said differently but with the same meaning:
>
> (1a) higher atomic number precedes lower;
> (1b) in comparing two duplicate nodes, lower root distance precedes higher
> root distance, where "root distance" for a duplicate node is defined as the
> distance from its corresponding nonduplicated atom node to the root node.
>
> Proposed amended rule:
>
> (1a) higher atomic number precedes lower;
> (1b) in comparing two duplicate nodes, lower root distance preceded higher
> root distance, where "root distance" is defined:
> (i) in the case of a duplicate atom for which the atomic number is averaged
> over two or more atoms in applying Rule 1a, the distance from the duplicate
> node itself to the root node; and
> (ii) in all other cases, the distance of its corresponding nonduplicated
> atom node to the root node.
>
> If that means nothing to you, ignore this. But it is a critically important
> addition for any algorithm if it is to correctly assign the stereochemistry
> even for very simple compounds based on CIP rules 1-5. For example, without
> that modification, an algorithm following the rules in IUPAC BB 2013 will
> arrive at "S" for the descriptor for in this compound:
>
>
> C1=CC=CC(O)=C1[C@H](C2=CC=CC=C2O)O
>
> My second question is, having said that, how do I go about officially stating
> this? Publish? Where?
>
>
> Bob
>
>
> --
> Robert M. Hanson
> Larson-Anderson Professor of Chemistry
> St. Olaf College
> Northfield, MN
> http://www.stolaf.edu/people/hansonr
>
>
> If nature does not answer first what we want,
> it is better to take what answer we get.
>
> -- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900
>
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