🚀 go-pugleaf

ib.mossin@hotmail.com wrote:
> 
> Hi,
> 
> Is there any sense in using the d,l system instead of the R,S system
> nowadays. The former seems a bit outdated.

There are systems in which R,S fails.  M,P for helicies, /_\,/\ for
octahedral complexes.  Geometrically undistorted point group T, O, and
I chiral systems (chiral by "color") simply cannot be named.

   1) Consider two geometrically congruent regular tetrahedra whose
mirror-image vertices host four different colors.  Unnameable as to
left and right but inarguably non-superposable.

   2) Consider an undistorted tetrahedral carbon bonded to four
identical asymmetric centers, CSSSS and CRRRR, point group T (not Td
or Th).  How do you assign configuration to that carbon?  Remove all
wiggle room by connecting all four substituents into a rigid skeleton,
[6.6]chiralane,

http://www.mazepath.com/uncleal/chiralan.htm

CSSSR and CRRRS are a similar problem.  The most entertaining
explanation I've heard is that the central carbon atom is NOT
asymmetric.  It is coincident with an asymmetric center.  Kewl. 
Assign configuration to that center.  Put three homochiral tartrates
(or tartrate acetonides) about an octahedral cobalt and calculate mm+
energy for mirror image octahedra in both configurations.  R-centers
tend to give most stable M helices and /\ coordination.  Except when
they don't.

Try to assign syndiotactic polypropylene as you attempt to identify
asymmetric carbons by expanding a sphere about a candidate tertiary
carbon.  The H and CH3 are obvious.  What makes the other two
substituents *locally* non-equivalent?  Now assign CIP R,S.

-- 
Uncle Al
http://www.mazepath.com/uncleal/
 (Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf