170 PREPARATION OF METHYLATED SUGARS 



be removed in definite steps. This behaviour is doubtless 

 controlled by causes similar to those which influence the partial 

 hydrolysis of a-fructose-diacetone. Irvine and Garrett have 

 shown that in the formation of this compound the addition of 

 the non-glucosidic acetone residue involves torsion of the 

 internal ring of the sugar molecule, but that the glucosidic 

 acetone group is differently linked and occasions less molecular 

 strain. The expressions trans and cis may be used to dis- 

 tinguish between the two types of linkage, and it has also 

 been shown that carefully regulated hydrolysis removes the 

 more unstable trans group, and thus a glucosidic monoacetone 

 derivative remains. These considerations are illustrated in 

 the formulae shown below : 



CHoOH.CH 



CH 2 



C(Me) a 

 . cis 



CH 2 OH.CH< OH H 



OH 



