tailieunhanh - Ebook Principles of organic chemistry: Part 2

This book provides context and structure for learning the fundamental principles of organic chemistry, enabling the reader to proceed from simple to complex examples in a systematic and logical way. | CHAPTER XV CARBOHYDRATES 346. Many organic compounds are produced as the result of the growth of plants. The more important of these such as starch sugar and cellulose are called carbohydrates. The name was originally given to the members of this class on account of the fact that the hydrogen and oxygen which they contain are present in the proportion in which these elements are present in water. The relation is shown by writing the formula for sugar C12H22O11 as H2O and for starch C6Hio05 as H2O . The formulas of certain carbohydrates which have been isolated from natural sources do not show the simple relation between the hydrogen and oxygen atoms indicated by the name. Rhamnose for example which is obtained from the bark of certain trees has the formula C6H12O5. A number of compounds which are not carbohydrates contain hydrogen and oxygen atoms in the relation of two of the former to one of the latter the formula of acetic acid is C2H1O2 of lactic acid C3H6O3 and so forth. Notwithstanding these facts the name carbohydrate is retained. The study of the structure of compounds of this class has made it possible to define the term more specifically. The carbohydrates are aldehyde-alcohols ketonealcohols or compounds which are converted by hydrolysis into aldehyde-alcohols or ketone-alcohols. The carbohydrates contain or are converted by hydrolysis into compounds which contain the arrangement of atoms represented by the formulas H H H H H T T i L 1 C C c o c c c H 11 I H J 0 0- 0 0 0 I 1 I 1 H H H H aldehyde-alcohol ketone-alcohol 325 326 ORGANIC CHEMISTRY The carbohydrates or saccharides as they are sometimes called are divided into two classes those which do not undergo hydrolysis are called monoses or monosaccharides J and those which are converted into monoses by hydrolysis are called polyoses or polysaccharides. When the monoses contain the aldehyde group they are classed as aldoses when they contain the ketone group they are called ketoses. The .