Which one of the following sets of monosaccharides forms sucrose ?

Options

A. `alpha-D-` Galactopyranose and `alpha-D-` Glucopyranose
B. `alpha-D-` Glucopyranose and `beta-D-` fructofuranose
C. `beta-D-` Glucopyranose and `beta-D` fructofuranose
D. `alpha-D-` Glucopyranose and `beta-D-` fructopyranose

Answer

B

Explanation

Acid-catalysed hydrolysis of 1 mol of surose `(C_(12) H_(22)O_(11))` yields 1 mol of D-glucose and 1 mol of an osazone and does not undergo nonreducing sugar, it does not form mean that neither the glucose nor the fructose portion of sucrose has a hemiacetal group. Thus, two hexoses must have a glycoside linkage that involes `C1` of glucose and `C2` of fructose, because only in this way will both carbonyl groups be present as full acetals (i.e., as glycodies).
Surcose is hydrolysed by an `alpha`-glucosidase obtained from yeast but not by `beta-`glycosidase enzymes. This hydrolysis indicates and `alpha` configuration at the glycosides portion. Sucrose is aslo hydrolysed by sucrase, and enzymes known to hydrolysis `beta`- fructofuranosides yields an octamethyl derivative that, on hydrolysis, yields 2.,3,4,5,6-tetra `-O-`methyl-D- fructose. The identities of these two products demonstrate that the glucose portion is a pyranoside and that the fructose portion is a furanoside.