CH.OH 



CH.OH 



This reaction is comparable to the conversion of an 

 optically active tartaric acid into the racemic form. Acids 

 like mannonic and gluconic acids, which contain a hydroxyl 

 group attached to a carbon atom in the 7 position to the 

 carboxyl group, readily form anhydrides known as lac tones. 

 Mannolactone would have the formula 



CO CH (OH)-CH(OH)CH CH(OH) CH 2 OH 



These substances, on treatment with nascent hydrogen 

 (obtained by adding sodium amalgam to an acid solution 

 of the lactone), are readily reduced to the aldehyde. In 

 this way mannolactone and glucolactone can be reduced to 

 mannose and glucose respectively. If, therefore, by the 

 above series of reactions, mannose can be converted into 

 glucose, the two sugars can differ from one another only 

 in the relative space positions of the hydrogen and the 

 hydroxyl group attached to the carbon atom next to the 

 aldehyde group. It is easy to see that sugars so related 

 should yield the same osazone, and this, in the case of 

 mannose and glucose, is indeed the fact. 



II. It is possible to convert one sugar into another in 

 which the positions of the CHO and CH 2 OH groups 

 are reversed ; that is, to convert 



