How many optically active isomers of `2,3-`dibromosuccinic acid are there?

Options

A. Two
B. Four
C. Three
D. Just one

Answer

A

Explanation

Molecule of `2,3-`dibromosuccinie acid, `HOOC CHBrCHBrCOOH`, contains to one identical chiral carbons as thr four ligands bonded to one chiral carbon atom `(CO_(2),H,H,Br` and `CHBrCO_(2)H)` are the same as those bonded to the second chiral atom. We can write four Fischer projections for this compound.

Configuration `I` and `II` are threo isomers while `III` and `IV` are erythro isomers. the thero pair are truly enantiomers as they are nonsuperposable and one is the refection of the other. a closer look at `III` and `IV` shows that they are in fact the same. If one configuration is roated through `180^(@)` (clockwise or anticlockwise in the plane of paper) it becomes identical with the other. This stereoisomer contains two chiral carbons by they are identical and cancel each other. The molecule as a whole is chiral. Thus this steroisomer (represented equally correctly by configuration `III` or `IV`) is not optically active.
Thus `2,3-`dibromosuccine acid can axist in the `(+)-` threo form, the `(-)-`threo form, as a racemic mixture of these two and as the inactive erytho form.