Cyclic Structure of Glucose
The cyclic structure of glucose has been proposed to explain those facts that could not be explained by the open-chain structure of glucose. In fact, the open-chain structure of glucose explained most of its properties, but the following facts could not be explained by this structure-
(1) Despite having the aldehyde group, glucose does not give Schiff’s test and it does not form the hydrogensulphite addition product with NaHSO3.
(2) The pentaacetate of glucose does not react with hydroxylamine indicating the absence of the free -CHO group.
(3) Glucose is found to exist in two different crystalline forms namely α and ꞵ-forms. The α-form of glucose (m.p. = 419K) is obtained by crystallization from a concentrated solution of glucose at 303K, while the ꞵ-form (m.p. = 423K) is obtained by crystallization from hot and saturated aqueous solution at 371K. This behavior could not be explained by the open-chain structure for glucose.
In fact, the -OH group of the fifth carbon atom of glucose molecule adds to the -CHO group and forms a cyclic hemiacetal structure. Thus, glucose forms a six-membered ring in which -OH at C-5 is involved in a ring formation. This explains the absence of -CHO group and also the existence of glucose in two cyclic forms which exist in equilibrium with open-chain structure.
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Important Tips for Preparation of IIT-JEE/NEET
- Select a good mentor for all the subjects. Several educational channels and the best mentors of Physics, Chemistry, and Biology are available on YouTube for free. You may follow one of them for all the subjects rather than wandering here and there.
- Centralize your study to the NCERT books and one reference book each for Physics, Chemistry, and Biology. Don’t follow too many books otherwise, you would not be able to complete your syllabus. Always remember, different books differ being only nineteen or twenty in text quality, but never differ of being nineteen and twenty-five.
- Follow quality notes of a good mentor for all the subjects. Don’t run behind the brand, but run behind the concise and effective notes of your mentor.
- Make your own capsule notes for revision.
- Maintain consistency and regularity in your preparation.
- Revise the prepared topics regularly. Always remember, revision is not a waste of time but it makes you perfect. Always keep in mind that, “Revision is division” i.e. Revision improves your marks and ultimately your rank in the final selection.
- Solve practice problems and previous year’s papers in the specified time frame. It would help you to finish your paper timely in the final examination.
- Always be confident in your preparation but never be overconfident. Always read the question carefully and then answer. You usually make mistakes in overconfidence and it has to be reduced.
Important Reference Books
(1) Physics- (1) Concept of Physics by H.C. Verma
(2) Modern’s abc of Objective Physics
(2) Chemistry- (1) Dr. O.P. Tandon (GRB Publication)
(2) Modern’s abc of Objective Chemistry
(3) Biology- (1) Biology by Trueman
(2) Modern’s abc of Objective Biology
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About Shailendra Shukla Sir
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