Erythro- prefix

The two stereoisomeric furanose forms of d erythrose are named a d erythro furanose and p d erythrofuranose The prefixes a and p describe fhe relative configu ration of fhe anomeric carbon The configurafion of fhe anomeric carbon is compared wifh fhaf of fhe highesf numbered chiralify cenfer m fhe molecule—fhe one fhaf defer mines whefher fhe carbohydrafe is d or l Chemisfs use a simplified informal version of fhe lUPAC rules for assigning a and p fhaf holds for carbohydrates up fo and mclud mg hexoses... 

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. 

For many open-chain compounds, prefixes are used that are derived from the names of the corresponding sugars and that describe the whole system rather than each chiral center separately. Two such common prefixes are erythro- and threo-, which are applied to systems containing two stereogenic carbons when two of the groups are the same and the third is different. The erythro pair has the identical Y Y Y Y... 

The relative configuration of adjacent, constitutionally non-equivalent, carbon atoms can be specified as erythro or threo, as appropriate, by adding the required prefix to the terms diisotactic and disyndiotactic , as necessary (see Section 2.2). 

Relative configurations at two contiguous carbon atoms in main chains bearing, respectively, substituents a and b (a b), are designated by the prefix erythro or threo, as appropriate, by analogy with the terminology for carbohydrate systems [6] in which the substituents are -OH. 

The term "racemo" is introduced here as the logical prefix for the designation of an arrangement that is analogous to racemic, in the sense defined above. It is unfortunate that the meaning of the term racemic current in organic chemistry is not directly applicable to polymers, but the use of the prefix "racemo proposed here should not cause confusion because of the special context. To achieve a full configurational description, it may be necessary to preface the name of a polymer with a compound adjective that combines a term such as erythro, threo, meso or racemo with a term such as diisotactic or disyndiotactic . 

The two sets of diastereomers are differentiated by the prefix erythro for the set in which at least two identical or similar substituents on chiral C s are eclipsed. The other set is called threo. 

EXTENSIONS AND COMMENT ARY Here is another example of the presentation of a compound for which there has not yet been an effective level determined. Why For a very good reason. This is an example of a whole class of compounds that I have called the pseudos, or the -compounds. Pseudo- as a prefix in the literary world generally stands for false. A pseudopod is a thing that looks like a foot, but isn t one. A pseudonym is a fictitious name. But in chemistry, it has quite a different meaning. If something has a common name, and there is a second form (or isomer, or shape, or orientation) that is possible and it doesn t have a common name, it can be given the name of the first form with a pseudo- attached. Ephedrine is the erythro-isomer of N-methyl-13-hydroxyamphetamine. There is a second stereoisomer, the threo- isomer, but it has no trivial name. So it is called pseudoephedrine, or the Sudafed of sinus decongestant fame. 

The relative configurations at two contiguous carbon atoms in these monomer units are designated by the prefix erythro or threo. 

In reading Nef s description of these substances and their preparation, it must be borne in mind that the available, naturally occurring D-xylose was at that time called i-xylose. Moreover, Rosanoff s convention for assigning configurational prefixes was then relatively new and was not utilized by Nef. Accordingly, Nef s 1-xylose and 1-arabinose, and d-erythro-, l-threo-, l-erythro-, and d-[Pg.41]

Two common prefixes used to distinguish diastereomers are threo and erythro. When drawn in the Fischer projection the erythro isomer has two identical substituents on the same side and the threo isomer has them on opposite sites. 

Polymerization of 1,4-disubstituted butadienes can lead to products that possess two asymmetric carbon atoms and one double bond in each repeat unit. Such tritactic polymers are named with prefixes of cis or trans together with erythro or threo (see Fig. 1.13). 

The terms isotactic and syndiotactic refer as above to the structure of each diasteric atom relative to comparable atoms in the other repeating units. The prefix erythro indicates that when a pair of adjacent diasteric atoms is rotated into an eclipsed conformation, at least two similar substituents can be superimposed. Threo denotes the nonsuperimposable isomer. In a disyndiotactic polymer each diasteric center is erythro to one of its neighbors and threo to the other, so there is only one isomer. 

Certain diastereomeric relationships are designated by prefixes derived from two carbohydrates. o-Threose (3.2) and D-erythrose (3.3) have two stereogenic atoms and both bear an -H and an -OH group. Other molecules that differ in the analogous fashion are prefixed threo- and erythro-, as generally represented in Figure 3.5. 

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