Question

(a)
Write about erythro- and threo-isomers of
an optically active compound.
​

Answer 1

ERYTHRO, THREO

The terms erythro and threo are derived from the nomenclature of the carbohydrates erythrose and threose. The relative configuration at adjacent chirality centers may be described by these terms. If identical or similar substituents are on the same side of the vertical chain in the Fischer projection, the erythro isomer is shown. If the substituents are opposite each other, the threo isomer is shown in the Fischer projection. Today, the erythro, threo nomenclature is still used only in carbohydrate chemistry.