The Role of Dissymmetry 101 



involvement in reactions might evoke the formation of optically active compounds. 

 This mistake became obvious after 1894 when P. Curie [55] formulated the re- 

 quirements which must be fulfilled by a dissynmietrical agent if it is to be able 

 to lead to the formation of asymmetry by influencing reactions; elliptically or 

 circularly polarized hght could constitute such an agent. 



Another reason for the lack of success in achieving asymmetric syntheses was 

 the choice of agents which had no effect on the reaction in question [56]. 



Thus, the dissymmetrical agent must not only be able to evoke dissymmetry 

 but must also be able to initiate the reaction [57]. 



These two requirements were met in experimental work devoted to the photo- 

 chemical asymmetric resolution of racemates and the asymmetric synthesis of 

 optically active compounds, when the agent evoking the dissymmetry was 

 circularly polarized light. Both the necessary conditions were satisfactorily 

 fulfiUed. 



ABSOLUTE ASYMMETRIC SYNTHESIS UNDER THE 

 INFLUENCE OF CIRCULARLY POLARIZED LIGHT 



I. Asymmetric decomposition of racemates. Scattered sunhght, when reflected 

 from the surface of the Earth under the influence of its magnetic field, becomes 

 partly circularly polarized with a slight preponderance of the right-handed com- 

 ponent [58-61]. The suggestion has been made that, owing to the effect of this 

 component being in excess, there occurred, during the course of the long years 

 of evolution of the living world, a regular biosynthesis of optically active organic 

 compounds [62-64], 



This hypothesis, which was first put forward by Van't Hoflf, seemed very 

 attractive and provided a stimulus for researches into the experimental condi- 

 tions required for the accomphshment of absolute asymmetric synthesis 

 under the influence of circularly polarized light in which one component pre- 

 ponderated. 



The photochemical effect of linearly polarized Hght on organic compounds 

 was discovered in 1841 but statements about its selective effect on optical anti- 

 podes were mistaken [65]. A selective action on antipodes can only be expected 

 from circularly polarized light [66, 67]. 



The first attempts to demonstrate this effect experimentally were unsuccessful 

 [68] and only Cotton [69] succeeded in discovering circular dichroism — different 

 degrees of absorption of circularly polarized hght by the optical antipodes of the 

 racemic tartrates of chromium or cobalt — a phenomenon which has been called 

 the Cotton effect [70]. It should be noted that McKenzie [71] had already tried 

 to carry out the asymmetric decomposition of salts of racemic lactic acid under 

 the influence of circularly polarized Hght. 



After it has been established that optical antipodes have different capacities 

 for the selective absorption of light which is circularly polarized in one direction, 

 many attempts were made to use this dissymmetric factor for the selective 

 decomposition of racemates. 



