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:
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.
Source:
