Question

Following are stereo representation for the three stereoisomer of 2, 3-butanediol. Out of I, II and III meso compounds is/are 

(1) only I

(2) only II

(3) both I and II

(4) both I and III

Answer 1

Meso compounds are compound which have chiral carbons (stereocenter) but compound is optically in active due to presence of plane of symmetry or centre of symmetry

∴ Compound-1 does not have plane of symmetry or centre of symmetry. So it is not meso compound.

(2)

∴ Compound-2, has plane of symmetry as well as centre of symmetry. So that it is a meso compound and optically inactive.

(3)

∴ Compound-3, does not have plane of symmetry or centre of symmetry. So that, it is nota a meso compound. it is optically active.

Hence, option (2) is right answer.