🚀 go-pugleaf

<ib.mossin@hotmail.com> wrote in message 
news:1154723407.301122.27420@m73g2000cwd.googlegroups.com...
> Hi,
>
> Is there any sense in using the d,l system instead of the R,S system
> nowadays. The former seems a bit outdated.

They're not overlapping systems.  d and l refer to the rotation of plane 
polarized light by a compound, and speaks to the chirality of the molecule 
as a whole.  R and S refer to absolute stereochemistry of one stereocenter, 
and are generally used with an indicator of what stereocenter is being 
identified--for example, 2R,3S-2,3-pentanediol.  Obviously, if you have a 
molecule with only one stereocenter, either convention can both be used.  To 
add further confusion, there are also D and L, which are used for sugars 
(aldoses) as an absolute indicator of stereochemistry, and refer to the 
configuration of the stereocenter right next to the aldehyde, relative to 
either D or L glyceraldehyde (if my rusty 25 year old memory serves 
correctly).  I don't know if, for all sugars, the D isomer (same 
stereochemistry as D-glyceraldehyde, which rotates polarized light to the 
right) is the same as the d isomer (the sugar itself rotates plane-polarized 
light to the right.)  There is yet another use of D and L, for amino acids, 
but I'm not certain how they're defined--probably relative to alanine, but 
I'm not sure.

Sometimes the rotation of polarized light is the only data you have on a 
molecule (for example, a new natural product) that carries any information 
about the stereoisomerism, and so d and l are the only designation that 
makes sense.  Once a molecule is better structurally characterized, either 
by a crystal structure or by synthesis starting with molecules of known 
absolute stereochemistry and using reactions of known absolute and relative 
stereochemical preferences, then designating each of the chiral centers in 
the molecule as either R or S becomes possible.

Eric Lucas