CBSE 2025 · Region 5 · Set 1 · Q29 · 4 marks
Carbohydrates are polyhydroxy aldehydes or ketones that represent enormous structural diversity in terms of the arrangement of atoms in space, resulting in hundreds of stereoisomers. Although the chemical properties of most stereoisomers may not be very different, their metabolic rate and utilization in biological systems is significantly different and known to influence the overall carbohydrate metabolism. Structural variants, which arise due to a different arrangement of atoms in three-dimensional space are known as stereoisomers. The number of stereoisomers can be theoretically estimated by using the formula 2n, where 'n' is the number of stereocenters or asymmetric (chiral) carbon atoms in a molecule. Out of these stereoisomers, there are some structures, which are mirror images of each other, and they are referred to as enantiomers. Answer the following questions :(a)Give chemical reactions to show the presence of an aldehydic group and straight chain in glucose.(b)Define anomers.(ii)Draw the structure of $\displaystyle \beta$-D-Glucopyranose.(c)Sucrose is known as invert sugar. Explain.
Carbohydrates are polyhydroxy aldehydes or ketones that represent enormous structural diversity in terms of the arrangement of atoms in space, resulting in hundreds of stereoisomers. Although the chemical properties of most stereoisomers may not be very different, their metabolic rate and utilization in biological systems is significantly different and known to influence the overall carbohydrate metabolism. Structural variants, which arise due to a different arrangement of atoms in three-dimensional space are known as stereoisomers. The number of stereoisomers can be theoretically estimated by using the formula 2n, where 'n' is the number of stereocenters or asymmetric (chiral) carbon atoms in a molecule. Out of these stereoisomers, there are some structures, which are mirror images of each other, and they are referred to as enantiomers. Answer the following questions :
(a)
Give chemical reactions to show the presence of an aldehydic group and straight chain in glucose.
(b)
Define anomers.
(ii)
Draw the structure of $\displaystyle \beta$-D-Glucopyranose.
(c)
Sucrose is known as invert sugar. Explain.
Marking-scheme solution
(a)
(b)(i)
Cyclic structures of glucose differ only in configuration of -OH group at C1. / Stereoisomers
which differ in configuration of -OH group at C1 or C2
(b)
(ii)
(c)
Hydrolysis of dextrorotatory sucrose brings a change in the sign of rotation or inverts the
optical rotation from dextro to laevo. The product of hydrolysis is invert sugar.
BiomoleculesCarbohydratesApplycase_studymedium
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CBSE Class 12 Chemistry past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.