Bottom asymmetric carbon

Therefore all forms in which the bottom asymmetric carbon atom possesses the same configuration as D-glyceraldehyde are said to belong to the D-series and their enantiomorphs to the L-series. 

The shortcoming of the system is that the configuration of only one (bottom) asymmetric carbon is specified while the configurations of the remaining ones remain hidden. 

Glucose on oxidation gives saccharic acid and on the basis of D-glucose structure, XIV would be D and XV, L on the account of the bottom asymmetric carbon atom. But if XV is rotated in the plane of paper through 180° if becomes exactly identical with XIV. Dispute like this and tartaric acid have raised great interest in improving the system of nomenclature. 

Figure 23-2 shows that degradation (covered in Section 23-14) removes the aldehyde carbon atom, and it is the bottom asymmetric carbon in the Fischer projection (the asymmetric carbon farthest removed from the carbonyl group) that determines which enantiomer of glyceraldehyde is formed by successive degradations. 

Most naturally occurring sugars are of the D series, with the OH group of the bottom asymmetric carbon on the right in the Fischer projection. 

Which configuration (R or S) does the bottom asymmetric carbon have for the D series of sugars Which configuration for the L series ... 

---