54 CARBOHYDRATES MONOSACCHATMJ2ES -^ 



X . 



possible to prepare a sugar containing six atoms of carbon in the mole- 

 cule, by the action of dilute alkali. At the same time Fischer succeeded 

 in synthesizing a hexose (that is to say, a six carbon atom sugar) from 

 its elements, by the polymerization of formaldehyde (HCHO), in 

 accordance with the equation: 



6HCHO = C 6 Hi 2 O 6 



and this sugar was found to be identical with that which had been 

 synthesized from glycerose. 



Examination of this new sugar showed, however, that it differed in a 

 very important property from the naturally occurring hexoses, fruit- 

 sugar, glucose, or mannose. These sugars, when in solution, rotate 

 the plane of polarization of a beam of polarized light to the right or 

 to the left. The synthetic sugar did not rotate the plane of polarized 

 light, and hence a special name was given to it, Across. 



The reason for the optical inactivity of acrose was found to lie in the 

 fact that it is a mixture of equal parts of optical antipodes, the one 

 rotating the plane of polarized light to the right, and the other to the 

 left in equal degree. As a matter of fact acrose can be decomposed by 

 appropriate measures into optically active constituents, and according 

 to the conditions which accompany the transformation we obtain 

 fruit-sugar, mannose, or glucose. 



It is a remarkable fact that nearly all natural products which are 

 derived from living material are possessed in some degree of Optical 

 Activity. This was at first thought to be a peculiarity of substances 

 formed by living organisms and to point to the operation within living 

 tissues of some force peculiar to living matter. We now understand 

 that the optical activity of the constituents of living matter is due to 

 the circumstance of their synthesis in the presence or through the 

 agency of optically asymmetric catalyzers. 



The exact conditions upon which this property of optical activity 

 depends were first made clear by Le Bel and Van't Hoff in 1874. 

 Previously to this Pasteur had expressed the opinion, based upon his 

 fundamental observations on the differing crystal-forms of the right- 

 handed and left-handed varieties of tartaric acid, that the optical 

 activity of certain molecules must be attributable to a certain degree 

 of asymmetry of the molecule. This asymmetry, in the case of 

 carbon compounds, Van't Hoff was able to trace to the carbon atom. 

 If we imagine the four valencies of a carbon atom to be pointing 

 toward the four apices of a tetrahedron, of which the center is the 

 carbon atom, the following arrangements of four different masses are 

 possible: 



