erythro structures

in a polymer
Also contains definition of: threo structures in a polymer
https://doi.org/10.1351/goldbook.E02211
The @R05260@ at two contiguous carbon atoms in the main chain bearing, respectively, substituents a and b (a ≠ b), is designated by the prefix erythro or @E02212@, 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 @E02212@ designation is employed to denote the relative placements of those two substituents, one for each @B00574@ carbon atom, which rank highest according to the @ST06775@ Rule.
Source:
Purple Book, 1st ed., p. 36 [Terms]