L-notation

Fischer projections and d-l notation have proved to be so helpful m representing carbohydrate stereochemistry that the chemical and biochemical literature is replete with their use To read that literature you need to be acquainted with these devices as well as the more modern Cahn-Ingold-Prelog R S system... 

Fischer projections and d-l notation are commonly used to describe car bohydrate stereochemistry The standards are the enantiomers of glycer aldehyde... 

Glycine is the simplest ammo acid and the only one m Table 27 1 that is achiral The a carbon atom is a chirality center m all the others Configurations m ammo acids are normally specified by the d l notational system All the chiral ammo acids obtained from proteins have the l configuration at their a carbon atom meaning that the amine group IS at the left when a Fischer projection is arranged so the carboxyl group is at the top... 

TBP of RR E X2 (and/or R2EX2) will be in equilibrium with molecular complexes (MC), together with the components, in solutions (Scheme 2).20 22 Both X-E-X and E-X-X bonds are hypervalent 3c-4e.15e 20 According to the N-X-L notation, proposed by Martin,23 the hypervalent atoms in X-E-X (TBP) and E-X-X (MC) are represented by 10 t 4 and 10-X-2, respectively. The notation will be employed in this chapter. 

The R,S system is quite general and has many advantages (and a few disadvantages) compared with the d,l notation for simple molecules. For diastereomers, it provides much clearer notations than meso, erythro,1 and threo1 that have been used for many years to designate the configurations of achiral and chiral diastereomers having two chiral carbon atoms ... 

Figure 2 Examples of various geometries based on VSEPR rules. Also given is the N-X-L notation (Section 2.3). Note that the lone pair of electrons in SeCle is in a stereochemically inactive 4s orbital...

Elaborations of the d,l- notation found only in Beilstein (obsol.). de Diastereomeric excess. Analogous to enantiomeric excess, q.v. 

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