Which of the following pairs can be distinguished by Fehling's solution ?
Which of the following pairs can be distinguished by Fehling's solution ?
Glucose and fructose
Glucose and sucrose
Methanal and ethanal
Hydroxypropanone and benzaldehyde.
Solution
Glucose is a hemiacetal, so in presence of a base (alkaline medium is provided by Fehling's solution) it can develop - CHO group in the form of open chain structure which responds Fehling's solution. Sucrose is a glycoside (acetal), i.e. its hemiacetal $\mathrm{OH}$ groups (one due to glucose and another due to fructose) are not free, so it can't attain -CHO group. Hence it will not respond Fehling's solution.