Defined Optical Isomerism Of Lactic Acid.
Lactic acid (2-Hydroxypropanoic acid) is an example of a compound which shows optical isomerism It contains one asymmetric carbon atom.
Two 3 dimensional structures are possible for Lactic acid.
These components are not identical because they cannot be superimposed on each other. One is the mirror image of the other. Such nonsuperimposable mirror-image forms are optical isomers and are called enantiomers. Thus, three forms of lactic acid are known. Two are optically active and the third is optically inactive.
- (+)-Lactic Acid. It rotates the plane of polarised light to the right (clockwise direction) and is called dextrorotatory.
- (-)-Lactic Acid. It rotates the plane of polarised light to the left (anticlockwise direction) and is called laevorotatory. (-)-Lactic acid is the mirror image of (+)-Lactic acid and vice versa.
- (±)- Lactic Acid. It does not rotate the plane of polarised light. That is, it is optically inactive. It is an equimolar mixture of (+)-and (-)-forms(racemic mixture).
Isomers of Lactic acid. In the upper line, two three-dimensional structures are shown. In the lower line, a commonly used Fischer projection is given. The vertical lines represent bonds going away from the observer/reader and horizontal lines represent bonds coming toward the observer.