Number chiral

The particular aldotetrose just shown is called d erythrose The prefix d tells us that the configuration at the highest numbered chirality center is analogous to that of d (+) glyceraldehyde Its mirror image is l erythrose... 

Highest numbered chirality center has configuration analogous to that of D glyceraldehyde -... 

Relative to each other both hydroxyl groups are on the same side m Fischer pro jections of the erythrose enantiomers The remaining two stereoisomers have hydroxyl groups on opposite sides m their Fischer projections They are diastereomers of d and L erythrose and are called d and l threose The d and l prefixes again specify the con figuration of the highest numbered chirality center d Threose and l threose are enan tiomers of each other... 

The two stereoisomeric furanose forms of D-erythrose ae naned a-D-erythro-furanose and p-D-erythrofuranose. The prefixes a and p describe the relative configuration of the anorneric cabon. The configuration of the anorneric cabon is cornpaed with that of the highest numbered chirality center in the molecule—the one that determines whether the cabohydrate is d or l. Chemists use a simplified, informal version of the lUPAC rules for assigning a and p that holds for ca bohydrates up to and including hexoses. 

Each of these compounds has a prefix d- with the name. As we saw in Section 3.4.10, this indicates that the configuration at the highest numbered chiral centre is the same as that in D-(R)-(4-)-glyceraldehyde the alternative stereochemistry would be related to... 

Since the carbonyl group is planar and may be attacked from either side, two epimeric structures (anomers) are possible in each case, and in solution the two forms are frequently in equilibrium, because hemiacetal or hemiketal formation is reversible (see Section 7.2). The two anomers are designated a or P by comparison of the chiralities at the anomeric centre and at the highest numbered chiral centre. If these are the same (RS convention), the anomer is termed P, or a if they are different. In... 

Hydroxyl group at the highest numbered chiral carbon (C-5) is pointing to the right, i.e similar to D-glyceraldehyde... 

SAMPLE SOLUTION (a) The —OH group at the highest-numbered chirality center (C-3) is up, which places it to the left in the Fischer projection of the open-chain form. The stereoisomer belongs to the l series. The —OH group at the anomeric carbon (C-1) is down, making this the 3-furanose form. 

Notice also that several of the carbons are chiral. Carbohydrates are labeled D or L as follows When in a Fischer projection as shown, if the hydroxyl group on the highest numbered chiral carbon points to the right, the carbohydrate is labeled D if to the left, then L. 

When more than four chiral carbon atoms are present, an aldose is given two configurational prefixes, one for the four lowest-numbered chiral centers and one for the rest of the molecule. The configuration of the /zz g/zesr-numbered group is stated first. 

An additional complicating issue should be kept in mind when reading the seminal pre-1968 literature, myo-Inositol derivatives that are currently designated D configuration were assigned L configuration and vice versa in the literature published before 1968. The reasons for the pre-1968 nomenclature are as follows before 1968, rules of carbohydrate nomenclature dictated that the orientation of highest numbered chiral carbon, C-6 in this case, specify the... 

Each prefix is preceded by d- or l-, depending on the configuration of the highest-numbered chiral carbon atom in the Fischer projection of the prefix. 

Two configurations known as anomers may result from the formation of the ring. These are distinguished by the anomeric prefixes a- and p-, which relate the configuration of the anomeric carbon atom to the configuration at a reference chiral carbon atom (normally the highest-numbered chiral carbon atom). For example, consider the glucopyranoses ... 

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