NOMENCLATURE of the ALPHAand BETA SUGARS* HORACE S. ISBELL National Bureau of Standards, Washington, D. C.
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EASUREMENTS on the rates of oxidation of numerous sugars, which the writer made by the bromine oxidation method', not yet reported, divide these sugars into two groups. Examination reveals that for all the sugars in the first group the oxygen ring lies to the right and for all the sugars in thexecond group the oxygen ring lies to the left. The classification of sugars by Hudson's method does not take into account any similarity of chemical behavior. In order to classify the sugars in a more satisfactory manner than heretofore, the writer proposes to change the customary nomenclature by introducing the new criterion of the position of the oxygen ring, as in this way a correlation of the names with the chemical behavior is obtained. The customary nomenclature is based on whether a sugar belongs in the d or 1series; i n the d series the more dextrorotatory substance of an or-8 p i r is designated or, and in the 1 series 0. This nomenclature was suggested by Hudson2 before the sizes and positions of the oxygen rings were definitely known and before our present knowledge of strainless ring structures in which the valence bonds lie in definite directions.Vn the normal aldoses the hydroxyl united with the fifth carbon forms the oxygen ring so that its configuration determines the direction in which the ring is bent. Consequently, the oxygen ring in all normal aldo-d-hexoses lies to the right and in all normal aldo-1-hexoses to the left. In the heptoses and higher sugars the d and 1 classification depends on the configuration of the sixth or higher carbon, while the configuration of the fifth carbon determines the position of the ring. In the
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* Published with the approval of the Director of the Bureau of Standards. U. S. Department of Commerce. Received October
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4. 1934 .. . .. .
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normal pentoses the hydroxyl determining the d and 1 classification does not form the ring, and consequently the location of the ring is not fixed by the configuration. The rates of oxidation, recently determined by the writer for numerous sugars in which the configurations of the first carbons are known from the optical rotations and the positions of the oxygen rings are known from the configurations of the fifth carbons, show that when the glycosidic hydroxyl lies in the same direction as the oxygen forming the ring the sugar reacts with bromine water more slowly than when the hydroxyl is directed away from the ring. In view of these facts the following rule is proposed: When the oxygen ring lies to the right, as in d-glucose, the more dextrorotatory ntember of the a-8 pair shall be designated or, and the less dextrorolalory member 8; when !he oxygen r i q lies to the left, as in 1-glucose, the more levorokitory member shall be desipnnled a, and the less levorotatory j3. This rule is applicable to the furanoses as well as the pyranoses and to the derivatives of both. The reaction rates for the pentoses, sugars in which the positions of the rings are not known from the configurations, show that normal a-d-xylose, 8-d-lyxose, B-d-ribose, and 1-arabinose (i-191) are genetically related to the d-hexoses, and'their oxygen rings lie to the right. Consequently, the more dextrorotatory forms of these sugars and their derivatives can be properly designated or. This gives a satisfactory classificationof those modifications of arabinose for which4 several names are in current use, but does not alter the existing names of the more important sugars. The experimental data will be published in a forthcoming paper in which other proposed systems of nomenclature will be discussed.
ISBELL, 3. Am. C h m . Sac, 54,1592 (1932).
' HUDSON,ibid31, 66 (1909). 'F u s c ~Ckm. , Rm.,7,347 (1930).
' R ~ E EAND S~UENSEN, Kgl. Norskc Videnskob. Selskabs Skriflcr, No. 7.1933.
