Question
Discuss the optical activity of lactic acid.
✓
Answer
$(1)$ Lactic acid contains one asymmetric carbon atom which is attached to four different groups, $COOH, CH_3, OH$ and $H.$
$(2)$ Two different arrangements of these groups around the carbon atom are possible as shown in the figure. Hence, it exist as a pair of enantiomers. The two enantiomers are mirror images of each other and are non$-$superimposable.
$(3)$ Hence, lactic acid can exist in two different forms, $d-$Form and $l-$form, which are non$-$superimposable mirror images of each other. $d-$form rotates the plane of plane$-$polarized light to the right, while $l-$form rotates the same to the left.
$(4)$ A mixture containing equimolar amounts of the $d-$ and $l-$forms is a racemic mixture which is optically inactive $(dl -$ form$4$ This inactivity arises due to external compensation.
$(2)$ Two different arrangements of these groups around the carbon atom are possible as shown in the figure. Hence, it exist as a pair of enantiomers. The two enantiomers are mirror images of each other and are non$-$superimposable.
$(3)$ Hence, lactic acid can exist in two different forms, $d-$Form and $l-$form, which are non$-$superimposable mirror images of each other. $d-$form rotates the plane of plane$-$polarized light to the right, while $l-$form rotates the same to the left.
$(4)$ A mixture containing equimolar amounts of the $d-$ and $l-$forms is a racemic mixture which is optically inactive $(dl -$ form$4$ This inactivity arises due to external compensation.
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