Which of the following statements about `(+) -` sucrose is incorrect ?

Options

A. It does not possess a free aldehydic or ketonic group
B. It is a beta D - fructoside and an alpha D- glucoside
C. It exists I anomeric forms
D. It is fermented by yeast

Answer

C

Explanation

Sucrose does not reduce Tollen's or invertase reagent. It is a nonreducing Sugar., and in this respect it differs from the other disaccharides. Moreover, `(+)-` sucrose does not shown mutarotation in solution. All these facts indicate that `(+) `- sucrose does not contain a "free" aldehyde of ketone group. `(+) -` sucrose is made up of a D-glucose unit and a D-fructose unit. Since these in no "free" carbonyl group, it must b both a D-glucoside and a D-fructoside. The two hexose units are evidently joind by a glycoside linkage between `C - 1 ` of glucose and `C - 2` of fructose i.e. glucose and fructose are linked by the aldehyde group of the former and ketonic group of the latter. Only in this way the single link between the two units can effectively block both the carbonyl functions
Determination of te stereochemistry of the D-glucoside and D-fructoside linkages is complicated by the fact that both linkage are hydrolyzed at the same time. The results of X-ray studies and finally the synthesis of `(+)-` sucrose leads to the conclusion that `(+)-` sucrose is a beta D - fructoside and an aopha D-glucoside. It should be noted that the fructose molecule in sucrose exists as the furanose form, and that when sucrose is hydrolysed, it is the pyranose form of fructose which is isolated.
Sucrose solution fermented by yeast when the enzyme invertase hydrolyses sucrose to glucose and fructose, while the enzyme zymase these monosacchorides to ethyl alcohol:
`underset("Sucrose")(C_(12) H_(22) O_(11) + H_(2)) O overset("Invertase")rarr underset("glucose")(C_(6) H_(12) O_(6)) + underset("fructose")(C_(6) H_(12) O_(6))`
`underset("Glucose of fructose")(C_(6) H_(12) O_(6)) overset("Zymase")rarr underset("Ethanol")(2C_(2) H_(5) OH + 2 CO_(2))`