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By J. Aehlert (Auth.)

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T h e ß-isomers form a 1,6-anhydro ring b y the elimination of phenol whereas t h e a-isomers are affected only slowly or not a t all. Unless a Waiden inversion takes place in the formation of t h e a n h y d r o ring, it would be expected t h a t t h e reaction would t a k e place between groups having a eis relationship with respect t o t h e sugar ring. , the phenyl group a t carbon 1 and the p r i m a r y hydroxyl group a t carbon 6. D . The Representation of the Ring Structures of the Sugars.

I(2»+1) when η is an even number, and b y 2 ~ when η is a n odd number. T h u s , for the tartaric acids ( C O O H — C H O H — C H O H — C O O H ) , three isomers are possible; for t h e pentaric (hydroxyglutaric) acids (COOH— C H O H — C H O H — C H O H — C O O H ) , four isomers are possible. Fewer isomers can exist when the end groups are identical because of the symmetries which develop. T h u s in t h e compounds which have an odd n u m b e r of asymmetric carbon atoms, t h e central carbon has two a t t a c h e d groups which m a y have the same structure.

Fischer established the convention of calling ordinary glucose d-glucose and employed t h e prefix d- in a configurational sense to mean t h a t a rf-substance is derivable from d-glucose whereas a n Z-substance is derivable from Z-glucose. Hence, fructose was called d-fructose although it exhibits a levorotation. T h e Fischer system, however, was modified b y RosanofP in order t h a t certain ambiguities would be avoided. T h u s , t h e following transformations have been carried o u t . D-Glucose HCO I D-Glucuronic acid HCO I HCOH I HCOH HOCH HOCH I I HCOH I HCOH HCOH HCOH I 1 I HCOH I HOCH I HCOH I HCOH HCO I HCOH I HOCH I HCOH I H,COH I COOH + COOH HCO H 2C O H COOH D-Xylose I co 2 I HCOH HCOH HCOH HCOH I I HOCH I HCOH I I COOH COOH acid D-flfiwco-Saccharic Ea nc iadn t i o m o r pL-grfa/co-Saccharic hs I I HOCH I HCOH I H 2C O H D-Gulose E i t h e r of t h e enantiomorphous forms of saccharic acid m a y be produced from ordinary glucose as shown above.

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