Sucrose is dextrorotatory but the mixture obtained after hydrolysis is laevorotatory. Explain.

Explanation

Sucrose is dextrorotatory having `[alpha]_(D)=+66.5^(@)`. On hydrolysis with dilute acids or enzymes, it gives equimolar `D-(+)-` glucose and `D-(-)-` fructose
`underset("Sucrose")(C_(12)H_(22)O_(11))+H_(2)Ooverset(HCl)rarrunderset([alpha]_(D)=+52.4^(@))underset("D - (+) - glucose")(C_(6)H_(12)O_(6))+underset([alpha]_(D)=-92.4^(@))underset("D - (-) - Fructose")(C_(6)H_(12)O_(6))`
Since, `D-(-)-` fructose has larger specific rotation than `D-(+)-` glucose, the resulting mixture has specific rotation of `-39.9^(@)`. Therefore, the mixture is laevorotatory.