A CHANGEABLE CARBOHYDRATE MOLECULE
The changeable carbohydrate molecule here presented illustrates one hundred ten structures of the common sugars and their deriwatives. The model i s based on the "slide-rule" principle and the different structures can be changed easily and rapidly to illustrate the usual carbohydrate reactions. The author hopes that with the presentation of the "molecule" and a prm'ous chart (1) the use of charts and models may come to form a larger part of the teaching of chemistry in general. With the ever-increasing amount of knowledge that is accumulating in a given field i t becomes necessary to find some new methods that will elimi-
nate some of the unnecessary steps in the teaching of the particular subject and yet cover the essential material in a clear and understanding manner for the student. During the recent years much thought and time has been given to the presentation of a subject by means of charts, models, and other objects which aid the student through his sense of sight to comprehend more clearly the material and to !hi t more firmly in his mind. Outside the use of the periodic table charts and a few charts for typical or general reac1370
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tions in inorganic and organic chemistry, the use of charts has been somewhat limited. The "molecule," ar i t is called, herewith presented is intended to stimulate the interest in and at the same time elucidate more clearly the fundamental relations that exist between the sugars (especially the pentoses, the hexoses and some of their derivatives) by the use of an arrangement which, by means of a few simple movements, shows the structure of over one hundred of the carbohydrates and their derivatives. FIGURE ~.-&ALLOSE In a recent article (1) . . the author has presented a chart of the relations existing between the carbohydrates along with an explanation of the reactions that enable one to pass from one of the sugars to another. The present article is to supplement the chart and give the student a clearer conception of the structure of the carbohydrates and the close relations that exist between them.
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JOURNAL OF CHEMICAL EDUCATION
J a y , 1931
The principle upon which the molecule works is not a new one. The application to which it is put is new; that of showing the various structures of the carbohydrates and some of their derivatives by the use of the "sliding-rule strips." thereby eliminating the necessity of writing the structures. The making of such a molecule would make an excellent problem in a course of organic or carbohydrate chemistry. I t would give the student a clearer conception of the structure and reactions of the sugars than could be obtained in any other way. The use of a large one (a yard square) in the lecture room would aid not only in the presentation of the subject, but would enable the student to visualize the changes that occur during the usual reactions. Figure 1 shows the essential details of the molecule; (A) the blank, (B) the strips, and (C) the pockets. The size of the molecule can be adjusted to meet
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the individual requirements; the author's was made of three-ply white cardboard, 7" X 9", with strips 9/a" wide and approximately the lengths shown in Figure 1 (B). In order to place the symbols in the most desirable locations on the various strips, it is suggested that the strips be cut out and slipped into their respective places, and the symbols printed. Strips 1, 2, 9, and 10 are made to slide into pockets, which are made from heavy paper (see Figure 1,B) fastened in position on the reverse side of the molecule. When the strips are all in place and lettered, a piece of cardboard the size of the front of the molecule can he pasted or fastened to the back. This will not only serve as a protecting hack but will give the molecule a neater appearance. If a large molecule is desired for lecture-room purposes it could be made from plywood or wall board with tin slots for the strips to slide in. If two molecules are used and hung some distance apart, one for the reacting sugar and one for the sugar produced with the proper symbols for the reaction written on the blackboard, there is presented to the student an object lesson not soon forgotten. To see the changes which take place during the reaction is to fix it more firmly in the mind and through the use of structural molecules this is made possible. The accompanying photographs show a number of the structures ~ossibleto illustrate by changing the strips of the molecule By the correct manipulation of the strips it is possible to show the Structure of one hundred ten sugars or their derivatives. The following sugars are ones which the author has demonstrated with the molecule: 16 hexoses (8 d-forms and 8 l-forms), 16 monobasic hexonic acids, 16 dihasic hexonic acids, 16 hexo-nitrils, 8 pentoses, 8 monobasic pentonic acids, 8 pentanitrils, 8 hexanols, 4 pentanols, 4 ketohexoses, 4 tetroses, and 2 keto-pentoses. It is hoped with the presentation of the semi-automatic carbohydrate molecule that the studying and teaching of carbohydrate chemistry may be facilitated, and that charts and structural models may come to have a greater part in the scientific study and teaching of chemistry.
Literature Cited (1) EDDY,"A N e w Relationship Chart of the Carbohydrates," J. CHEM.EDUC.,7. 269W (Nov.. 1930).
