Which of the following statements is not true about glucose?a)It is an...
Glucose is present in pyranose form, i.e., five-membered ring structure. Thus, option (iii) is correct because the given statement is incorrect.
Glucose is a monosaccharide that is composed of six carbon atoms with an aldehyde group. Thus, it is an aldohexose. So, this statement is true and therefore, option (i) is incorrect.
Option (ii) is incorrect because the given statement is true. On heating glucose with HI, it forms n-hexane. This reaction suggests that all the six carbon atoms in glucose are linked in a straight chain.
Option (iv) is incorrect because the given statement is true. The aldehyde group is not free in the cyclic structure. So, it does not give 2, 4-DNP test.
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Which of the following statements is not true about glucose?a)It is an...
A) It is an aldohexose.
Glucose is indeed an aldohexose, meaning it is a hexose sugar with an aldehyde functional group. It has six carbon atoms in its structure, and the aldehyde group is located on the first carbon atom.
B) On heating with HI it forms n-hexane.
This statement is true. When glucose is heated with hydroiodic acid (HI), it undergoes a reaction called deoxyhydration. In this reaction, the hydroxyl groups (-OH) of glucose are substituted by iodine atoms (-I), resulting in the formation of n-hexane.
C) It is present in furanose form.
This statement is not true. Glucose exists primarily in the pyranose form, not the furanose form. Furanose refers to a five-membered ring structure, while pyranose refers to a six-membered ring structure. Glucose predominantly exists in the pyranose form, specifically in the alpha and beta anomers.
D) It does not give 2,4-DNP test.
This statement is not true. Glucose does give a positive 2,4-DNP (2,4-dinitrophenylhydrazine) test. The 2,4-DNP test is used to detect the presence of carbonyl groups, such as aldehydes and ketones. Glucose, being an aldose (aldohexose), contains an aldehyde group and thus can react with 2,4-DNP to form an orange-red precipitate.
In summary, the statement that is not true about glucose is:
C) It is present in furanose form.