ARTICLES 



THE GENERAL BEHAVIOUR OF 

 OPTICALLY ACTIVE COMPOUNDS 



By T. S. PATTERSON, D.Sc, Ph.D. 

 Gardiner Professor of Organic Chemistry, University, Glasgow 



When, in 1815, Biot first discovered that certain organic com- 

 pounds have the power of altering the plane of polarisation of 

 light, he thought this deviation was unaffected by change of 

 temperature, and solvent, and concentration ; and he suggested 

 the idea of a specific rotatory power for such a substance, which 

 ought to remain constant under all conditions. But he was not 

 long in discovering that his original notion was incorrect, and 

 it has been shown in more recent years that the optical activity 

 of a given compound is in general highly sensitive to external 

 conditions ; that it may vary in perplexing fashion, and to a 

 very considerable extent, according to the temperature, the 

 solvent, the concentration, and the wave-length of the light 

 used. Investigation, which generally follows the path of least 

 resistance, was, not unnaturally, first directed to the influence 

 of different solvents upon active compounds, but without any 

 very satisfactory results ; and it was perhaps the examination 

 of the rotation of active compounds at different temperatures, 

 first taken up systematically by P. F. Frankland, which led in 

 the end to conclusions of some general applicability. Some 

 twenty or twenty-five years ago it was known that the rotation 

 of a number of active substances often increased or decreased 

 fairly rapidly with rise of temperature ; and the opinion tacitly 

 held at that time, although perhaps not definitely expressed, 

 was, probably, that the rotation gradually rises to some definite 

 value, and thereafter remains practically constant, as shown in 

 Fig. I , by the curve DEFGHKL. In 1 896, however, Frankland 

 and Wharton {J.C.S., 1896, 69, 1587) first demonstrated that 

 this is not the case, since they found in the curve for ethyl 

 dibenzoyltartrate in the super-fused homogeneous ester at 

 a temperature of 60°, a distinct minimum^ specific rotation of 

 —62 '3°. It was then noticed by the present writer that a 



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