The data show that the sugars, the glucosidic compounds, and the 

 lactones, all of which contain the lactonic ring, have strong rotatory 

 powers. There are three apparent exceptions, /?-methyl galactosid, 

 /?-xylose, and ^-rhamnose, but for each of these the corresponding 

 a or /? isomer is strongly rotatory, proving that the slight rotations 

 of the three compounds are due to internal compensations, and that 

 they contain strongly active carbon atoms. On the other hand, the 

 alcohols and acids are of feeble rotatory powers, which are in general 

 not comparable with the strong rotations of the sugars, glucosidic 

 compounds and lac tones. There is thus satisfactory proof that the 

 lactonic ring structure causes a strong rotation. 



The rotations of the alcohols and acids recorded are so small in 

 comparison with those of the lactones that the rotations of the latter 

 may be assumed to be due, as a first approximation, entirely to the 

 lactonic ring. There are two possible stereo structures for the lac- 



C C C CO and C C C 



tonic ring, namely C C C CO and C C C CO, which are 



mirror images (with the mirror placed horizontally). If the rotation 

 of the lactone is due entirely to this ring the position of the ring must 

 determine the sign of the rotation of the lactone. The position of 

 the ring is determined by the position which the OH group had on 

 the ^-carbon atom before the ring was formed. These ideas thus 

 lead to the following hypothesis : Lactones of dextrorotation have the 

 lactonic ring on one side of the structure, lactones of levorotation have 

 it on the other, and the position of the ring shows the former position 

 of the OH group on the ^-carbon atom. 



TEST OF THE HYPOTHESIS. 



This hypothesis will now be tested. In Table 2 there are collected 

 the structural formulas and specific rotations of 24 lactones of the 

 monobasic sugar acids, including every such lactone for which the 

 structure and specific rotation have been determined. The first column 

 gives the name and the second the stereo configuration of the lactone, 

 the discovery of which is due in all cases to the immortal researches 

 of Emil Fischer. In the third column is the statement, for con- 

 venience, of the position of the lactonic ring, whether " above" or 

 " below" the chain, and in column 4 are the specific rotations of 

 the lactones, which are quoted from Lippmann's "Chemie der Zuck- 

 erarten." In most cases they were measured by Emil Fischer or 

 his students. 



a The stereo formulas will be written horizontally to save space. 

 [Cir. 49J 



