56 



CA RBOH YDRA TESM ON OS A CCHA RIDES 



This will be rendered clearer by the accompanying diagram, which 

 illustrates the structure of the sixteen possible stereo-isomers of any 

 compound which contains four asymmetric carbon atoms. Designat- 

 ing a dextrorotatory carbon by the symbol + and a levorotatory 

 carbon by the symbol it will be seen that each carbon is dextrorotatory 

 in eight isomers, and levorotatory in eight others. It is also evident 

 that provided the end-groups attached respectively to the first and 

 fourth asymmetric carbons are identical, the isomer number 11 is 

 identical with the isomer number 5, 12 with 6, 13 with 7 and so forth. 



11 



12 



13 



14 



15 



16 



10 



This is what actually occurs in the corresponding polyatomic alcohols, in 

 which the CHO group of the sugar is replaced by the group CH 2 OH. 

 In the hexoses, of which glucose is a representative, the two end- 

 groups are, of course, different and hence no two possible isomers are 

 identical. There are, therefore, 16 possible sugars or hexoses of the 

 aldehyde type, possessing the above formula. We may represent them 

 as follows, using the prefixes d- and 1- to signify dextro- and levo- 

 rotatory respectively. 



CHO 



I 



H C OH 

 H C OH 

 HO C H 

 HO C H 



CH 2 OH 



1-mannose. 

 CHO 



HO C H 



I 

 H C OH 



HO C H 

 H C OH 



s OHsOH 



1-idosc. 



CHO 



HO C H 

 HO C H 

 H C OH 

 H C OH 



CH 2 OH 



d-mannose. 

 CHO 



H C OH 



HO C H 



I 

 H C OH 



HO C H 



I 



CH 2 OH 

 d-idoso. 



CHO 



HO C H 



H C OH 

 HO C H 



HO C H 



I 



CH 2 OH 

 1-glucose. 

 CHO 



H C OH 

 H C OH 

 HO C H 

 H C OH 



CH 2 OH 



l-galose. 



CHO 



H C OH 

 HO C H 

 H C OH 

 H C OH 



CH 2 OH 

 d-glucose. 

 CHO 

 I 

 HO C H 



I 

 HO C H 



I 

 H C OH 



HO C OH 



I 

 CH 2 OH 



d-galose. 



