STEREOISOMERISM AND OPTICAL 



ACTIVITY 



A CRITICAL STUDY, WITH A NEW SUGGESTION 



Bv G. S. AGASHE, M.Sc. (Manchester), M.A. (Bombay) 



PART I.— INTRODUCTORY 



In the year 1808 Malus discovered the phenomenon of the 

 polarisation of light. His pupil Arago discovered that quartz 

 crystals possessed the power of rotating the plane of polarisation 

 of polarised light, i.e. they were optically active. He further 

 noticed that there were two modifications of crystalline quartz, 

 which rotated the plane of polarisation in opposite directions. 



Some years before, Abbe Hauy had noticed that there were 

 two kinds of quartz crystals, possessing hemihedral facets on 

 opposite sides of the crystal, thus constituting what are called 

 enantiomorphous forms. 



These two independent observations of Arago and Hauy 

 were brought together by Sir John Herschel, who, in 1820, 

 suggested a possible connection between the two phenomena 

 of opposite rotation and the reversed position of facets on the 

 crystals. 



In the meanwhile (181 5) Biot had discovered that many 

 natural organic substances like sugar, oil of turpentine, and 

 tartaric acid were optically active in the liquid or dissolved state. 

 He also pointed out the difference between these substances and 

 quartz, which loses optical activity, when the crystalline form is 

 destroyed. But the suggestion of Herschel, just mentioned, was 

 first applied to such substances by Pasteur, 1 who, in 1848, 

 succeeded in preparing from sodium ammonium racemate 

 (optically inactive) a mixture of sodium ammonium dextro- and 

 laevo-tartrates, showing oppositely situated hemihedral facets, 

 the crystals of the dextro-salt having them on the right, and 

 those of the laevo-salt on the left. 



1 Chemical Society Pasteur Memorial Lecture, 1897. 



227 



