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प्रश्न
On the basis of which evidences D-glucose was assigned the following structure?
\[\begin{array}{cc}
\ce{CHO}\\
|\phantom{....}\\
\phantom{..}\ce{(CHOH)4}\\
|\phantom{....}\\
\phantom{..}\ce{CH2OH}
\end{array}\]
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उत्तर
This structure was assigned on the basis of the following evidences:
1. Molecular formula: The molecular formula of glucose has been found to be \[\ce{C6H12O6}\].
2. Straight chain structure:
(i) When aqueous solution of glucose is treated with sodium amalgam (Na/Hg) or sodium borohydride, it is reduced to sorbitol (or glucitol) a hexahedric alcohol.
\[\begin{array}{cc}
\phantom{.}\ce{CHO}\phantom{.......................}\ce{CH2OH}\phantom{..}\\
\phantom{}|\phantom{...........................}|\phantom{........}\\
\ce{(CHOH)4 + 2[H] ->[Na amalgam] (CHOH)4}\\
\phantom{}|\phantom{...........................}|\phantom{........}\\\
\phantom{..}\ce{CH2OH}\phantom{....................}\ce{\underset{Sorbitol}{CH2OH}\phantom{....}}
\end{array}\]
(ii) Prolonged heating with hydriodic acid and red phosphorus at 100°C gives a mixture of n-hexane and 2-iodohexane.
\[\begin{array}{cc}
\ce{\underset{Glucose}{CH2OH(CHOH)4CHO} ->[Hl][red P, 100°C] \underset{n-hexane}{CH3(CH2)4CH3} + CH3CH(CH2)3CH3}\\
\phantom{............................................}|\\
\phantom{............................................}\ce{\underset{2-Iodohexane}{I}}
\end{array}\]
The formation of n-hexane suggests that all the six carbon atoms in glucose are arranged in a straight chain structure of glucose.
3. Presence of five hydroxyl (-OH) groups: On acetylation with acetic anhydride, glucose gives a pentaacetate. This confirms that glucose contains five –OH groups. We know that the presence of two or more –OH groups on the same carbon atom makes the molecules unstable. Now since glucose is a stable compound, therefore, the five -OH groups must present on different carbon atoms.
4. Presence of one primary alcoholic group: On oxidation with cone, nitric acid, both glucose and gluconic acid give the same dicarboxylic acid, saccharic acid or glucaric acid. The primary alcoholic group \[\ce{(CH2OH)}\] is always present at the end of the carbon chain.
5. Presence of an aldehyde (-CHO) group: Glucose reacts with hydroxylamine, \[\ce{NH2OH}\] to form glucose CHO oxime. Which suggest that glucose contains a carbonyl \[\ce{(CHOH)4}\] (>C = O) groups.
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संबंधित प्रश्न
Write the reaction that indicates the presence of -CHO group in glucose
Write the product when D-glucose reacts with conc. HNO3.
Write the reactions involved when D-glucose is treated with the following reagent:
H2N-OH
The number of asymmetric carbon atom(s) below the figure is/are
What is the most abundant organic compound on earth?
Which one of the following compounds is different from the rest?
Glucose reacts with acetic anhydride to form ______.
The number of chiral carbons in ß-D(+) glucose is ____________.
Which one is correct?
Which one of the following reactions is not explained by the open chain Structure of glucose?
In the following reaction, identify A and B:
\[\begin{array}{cc}
\ce{C6H12O6 ->[Acetic anhydride] A}\\
\downarrow \text{Conc. nitric acid}\phantom{...}\\
\ce{B}\phantom{.................}\end{array}\]
Which of the following pairs represents anomers?
Three structures are given below in which two glucose units are linked. Which of these linkages between glucose units are between C1 and C4 and which linkages are between C1 and C6?
| (I) |  |
| (II) |  |
| (III) |  |
Assertion: D (+) – Glucose is dextrorotatory in nature.
Reason: ‘D’ represents its dextrorotatory nature.
Write the reactions of D-glucose which can’t be explained by its open-chain structure. How can cyclic structure of glucose explain these reactions?
Account for the following:
There are 5 OH groups in glucose
Account for the following:
What happens when D – glucose is treated with the following reagents
Bromine water
Consider the following reactions:
(i) \[\ce{Glucose + R-OH ->[Conc. HNO3] [A] ->[X eq of][(CH3CO)2O] Acetyl derivative}\]
(ii) \[\ce{Glucose ->[Ni/H2] [A] ->[Y eq of][(CH3CO)2O] Acetyl derivative}\]
(iii) \[\ce{Glucose ->[Z eq of][(CH3CO)2O] Acetyl derivative}\]
'X, 'Y' and 'Z' in these reactions are respectively:
Give a reason for the following observations:
Penta-acetate of glucose does not react with hydroxylamine.
