52 



SCIENCE 



[N. S. Vol. XLV. No. 1151 



two scientists working independently 

 reached almost identical conclusions at 

 about the same time, van't HofE presenting 

 his views in a brochure published at Utrecht 

 in September, 1874, while Le Bel's article 

 appeared two months later in the November 

 issue of the Bulletin de la Societe Chimi- 

 que de Paris. In accordance with the views 

 advanced by van't HofE and Le Bel every 

 molecule containing a carbon atom attached 

 to four different groups (a so-called asym- 

 metric carbon atom) may exist in two forms 

 related to each other as object is to image. 

 The one form of molecules rotates the plane 

 of polarization to the right, the other form 

 rotates it an equal extent to the left. It 

 follows, therefore, that a compound con- 

 taining an asymmetric atom may be ex- 

 pected to exist in three forms: the dextro 

 or d-lovnx composed of those molecules 

 which rotate the plane of polarization to 

 the right; the levo or Z-form composed of 

 those molecules which rotate the plane of 

 polarization to the left; and the inactive or 

 raeemic form which consists of a true chem- 

 ical combination of the two kinds of mol- 

 ecules in equal quantities. It is also pos- 

 sible to have equimolecular inactive mix- 

 tures of the dextro and levo forms. 



This theory of van't Hoff and Le Bel, 

 well known and therefore but briefly 

 sketched, was vigorously opposed and even 

 ridiculed when first advanced. Kolbe re- 

 ferred to it in the following terms : 



A Dr. J. H. van't Hoff, stationed at the veteri- 

 nary Bchool at XJtreclit, as it appears, finds no 

 pleasure in exact chemical investigations. He has 

 deemed it easier to mount Pegasus (evidently bor- 

 rowed from the veterinary school) and in his 

 ' ' Chemistry in Space ' ' to announce how the atoms 

 lying about in the universe, appeared to him from 

 the chemical Parnassus which he had climbed in 

 his bold flight. ... To criticize this writing even 

 in a half way thorough manner is not possible, be- 

 cause the fantastic absurdities are entirely lacking 

 in actual foundation and are entirely incompre- 

 hensible to the sober-minded investigator. 



Notwithstanding these criticisms the 

 theory advanced by van't Hoff and Le Bel 

 has stood the test of experiment better per- 

 haps than any other theory ever advanced 

 within the domain of organic chemistry and 

 has been a most potent factor in the devel- 

 opment of stereo-chemistry. 



THE SYNTHESIS OP ASYMMETRIC COMPOUNDS 



To me the most interesting problem be- 

 longing to the general subject of stereo- 

 chemistry is that of synthesizing com- 

 pounds containing an asymmetric group. 

 As stated above, compounds containing 

 such a group may exist in three forms. 

 The early attempts to synthesize such com- 

 pounds, however, always resulted in the 

 production of equal quantities of the dextro 

 and levo forms, which either remained as 

 mixtures or combined to produce the ra- 

 eemic form. As a result, the product ob- 

 tained was always optically inactive. There 

 is nothing remarkable in this result. In- 

 deed, it is just what one would expect ; for 

 so far as one is able to judge the chances 

 for the atoms to combine in one of the two 

 possible ways is the same as the chances for 

 them to combine in the other way. It 

 would naturally follow, therefore, that the 

 two possible forms of molecules will be pro- 

 duced in numbers that are equal, or are at 

 least approximately so. The remarkable 

 fact is not, therefore, that the synthetic 

 compound of the laboratory is optically in- 

 active or so nearly so that its activity can 

 not be detected by any instruments yet de- 

 vised, but rather that compounds occurring 

 in nature and containing an asymmetric 

 group with very few exceptions always 

 occur in the active form. In other words, 

 nature's synthetic methods result appar- 

 ently in the formation of the dextro or of 

 the levo form alone, while the synthetic 

 methods of the laboratory always lead to the 

 production of the two forms in equal quan- 



