The Role of Dissymmetry 103 



Far greater theoretical interest attaches to the experiments aimed at carrying 

 out absolute asymmetric syntheses of optically active compounds from sub- 

 stances which had a symmetrical structure. As a result of a reaction of this sort, 

 an asymmetric carbon atom appears in the product and the compound shows 

 optical activity. 



2. Photochemical, absolute, asymmetric synthesis. Genuine, absolute, asym- 

 metric synthesis, as distinct from the resolution of racemates, in the course of 

 which new centres of asymmetry came into being, was accomplished very soon 

 after Kuhn's experiments. 



The first attempts to carry out photochemical absolute asymmetric syntheses 

 by the bromination of substituted cinnamic acids [80] angelic acid [81] or by 

 adding HCN to acetaldehyde [82] were unsuccessful. 



Not until 1933-34 did Karagunis & Drikos [83] first bring about an absolute 

 asymmetric synthesis by adding chlorine to a free triarylmethyl radical under 

 the influence of circularly polarized light : 



R1R2R3C— + 1 CI2 -> R1R2R3C— CI 



During the reaction the magnitude of the rotation passed through a maximum, 

 reaching o-o8°. 



In the following year Tenney & Heggie [84] obtained optically active products 

 under the same conditions, adding bromine to 2 : 4 : 6-trinitrostilbene, while 

 Betti & Lucchi [85] found a small asymmetric effect on chlorinating propylene, 

 butylène and butadiene. 



Special interest attaches to the first absolute asymmetric synthesis of a natural 

 compound, carried out in 1945 by Tenney & Ackerman [86]. 



At first they obtained an optically active substance, (+)-tartaric acid, by the 

 action of circularly polarized fight, and it was in the very form in which it 

 occurs in Hving Nature. The s5Tithesis was completed by the hydroxylation with 

 hydrogen peroxide of diethyl fimiarate by illumination with circularly polarized 

 light. The rotation of the product passed through a maximum, reaching 

 +0-073° which corresponds to a degree of asymmetric synthesis of 2-5%. 



It should be added that (+)-tartaric acid is obtained by the action of the 

 right-handed component of circularly polarized fight and this is the component 

 which is present in sHght excess in scattered fight on the surface of the Earth as 

 we noted earfier. This fact provides strong support for the hypothesis that the 

 optical asymmetry of the molecular constituents of fiving organisms was brought 

 into being by the action of circularly polarized fight. 



A DISSYMMETRIC SEQUENCE AS A FACTOR IN LIFE 



In conclusion we wiU give some consideration to the significance of those 

 factors which we termed the Pasteur effect. 



Recent investigations have shown that polymers and polycondensates in which 

 the molecules are composed of unsymmetrical finks of a single type have special 

 properties, different from the properties of irregular polymers. This is caused 

 by the different and closer packing of regular chains [87]. 



