Q7 / 180 · COMEDK 2023 (Memory Based) · Chemistry

Pick out the incorrect statement(s) from the following. 1. Glucose exists in two different crystalline forms, $\alpha$-D-glucose and $\beta$-D-glucose. 2. $\alpha$-D-glucose and $\beta$-D-glucose are anomers. 3. $\alpha$-D-glucose and $\beta$-D-glucose are enantiomers. 4. Cellulose is a straight chain polysaccharide made of only $\beta$-D-glucose units. 5. Starch is a mixture of amylase and amylopectin, both contain unbranched chain of $\alpha$-D-glucose units.

  • A
    1 and 2 only
  • B
    2 and 3 only
  • C
    3 and 4 only
  • Correct answer
    D
    3 and 5 only

Solution

$\alpha$-D-glucose and $\beta$-glucose, differ in the orientation of $-\mathrm{H}$ and $-\mathrm{OH}$ groups are first carbon atom. Such isomers are called anomers. Starch is a mixture of amylase and amylopectin but amylase is a straight chain polymer while amylopectin is a branched chain polymer of $\alpha$-D-glucose.

Hence, the correct answer is option: 'D'.

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