“The optically active, polyhydroxy aldehydes or ketones or the compounds which produce these compounds on hydrolysis are called Carbohydrates”.
The most common examples of carbohydrates are cane sugar (C12H22O11), glucose (C6H12O6), fructose (C6H12O6), starch [(C6H10O5)n], cellulose, etc. Most of the carbohydrates have the general formula, Cx(H2O)y. For example, the molecular formula of glucose (C6H12O6) fits into this general formula, C6(H2O)6. However, all the compounds which fit into this formula may not be essentially carbohydrates. For example, acetic acid (CH3COOH) fits into this general formula, C2(H2O)2, but it is not a carbohydrate. Similarly, rhamnose, (C6H12O5) does not fit in this definition, but it is a carbohydrate.
Since, the ratio of hydrogen and oxygen atoms in carbohydrates are in general, the same as in water (2:1), they were considered as hydrates of carbon and named as carbohydrates. Now, it has been well established that, carbohydrates do not contain water and therefore, their name carbohydrate is erroneous, but because of being well established, it still persists.
Some of the carbohydrates, which are sweet in taste, are also called sugars. The most common sugar, used in our homes is sucrose, whereas the sugar present in milk is lactose. Carbohydrates are also called saccharides (Greek, sakcharon means sugar).
Classification of Carbohydrates
Carbohydrates are classified on the basis of their behavior on hydrolysis. They have been broadly divided into the following three groups-
(1)Monosaccharides- The simplest carbohydrates that cannot be hydrolyzed further to give the simpler unit of polyhydroxy aldehydes or ketones are called a monosaccharide. About 20 monosaccharides are known to found in nature. Some common examples are glucose (C6H12O6), fructose (C6H12O6), ribose (C5H10O5), etc.
(2)Oligosaccharides- Such carbohydrates which yield two to ten monosaccharide units on hydrolysis, are called oligosaccharides. They are further classified as disaccharides, trisaccharides, tetrasaccharides, etc., depending upon the number of monosaccharides, they give on hydrolysis.
The most common oligosaccharides are disaccharides. The two monosaccharide units obtained on hydrolysis of a disaccharide may be the same or different. For example, one molecule of sucrose (C12H22O11), on hydrolysis gives one molecule each of glucose and fructose, whereas one molecule of maltose (C12H22O11), on hydrolysis gives two molecules of glucose.
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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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Download pdf notes of chemistry for Class 11 from the following link-
Download pdf notes of chemistry for Class 12 (English Medium) from the following link-
Download pdf notes of chemistry for Class 12 (Hindi Medium) from the following link-
About Shailendra Shukla Sir
By profession, Shailendra Shukla Sir is a senior executive officer in a very reputed power generation company. He has been a professional teacher of competitive chemistry for a long time and his sole aim is to provide quality guidance to the aspirants of UPSC, State PSCs, IIT-JEE, AIIMS, NEET, and Academic examinations, especially to those who belong to the economically vulnerable class of society and cannot afford heavy tuition fees of professional institutions.
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