Meso butane`-2,3-`diol is optically inactive because

Options

A. it is an equal mixture of two enantiomers
B. it is an equal mixture of two diasteroemers
C. it is an equal mixture of an enantiomer and diadteromer
D. at least one conformer has either a plane or a point of symmetry which makes it superposable upon its mirror image

Answer

D

Explanation

We can draw meso-butane`-2-,3-diol` in the Fischer projection showing a plane of symmetry, in the sawhorse projection showing a plane in the eclipsed conformer and a point of symmetry in a staggered conformer.

We can also recognize a meso compound in the Newman projection. For this purpose rotate about the `C-C` bond until a staggered conformer `(A)` with a point of symmetry or an eclipsed conformation `(B)` with all ligands mathching up results

Note that meso-butane`-2,3-diol` can be called either `R,S` or `S,R` beacuse the `2R,3S` configuration is identical with the `2S,3R` configuration. Number are not necessary beacuse the two designations are equivalent.