Term: erythro structures
https://doi.org/10.1351/goldbook.E02211

Definition:
The relative configuration at two contiguous carbon atoms in the main chain bearing, respectively, substituents a and b (a ≠ b), is designated by the prefix erythro or threo, as appropriate, by analogy with the terminology for carbohydrate systems in which the substituents are OH. Examples: E02211.png Similar systems in which a higher level of substitution exists may be treated analogously if the erythro or threo designation is employed to denote the relative placements of those two substituents, one for each backbone carbon atom, which rank highest according to the Sequence Rule.

Related Terms:
1) relative configuration (http://doi.org/10.1351/goldbook.R05260).
2) threo (http://doi.org/10.1351/goldbook.E02212).
3) backbone (http://doi.org/10.1351/goldbook.B00574).
4) sequence (http://doi.org/10.1351/goldbook.ST06775).

Image: Not defined (https://goldbook.iupac.org/img/inline/E02211.png) 

Source: Purple Book, 1st ed., p. 36 (http://old.iupac.org/publications/books/author/metanomski.html)

Citation: '<i>erythro</i> structures' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.E02211

License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.

Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.