Electron Theory in Organic Chemistry. 673 



Now in our model of the molecule it can easily be seen 

 that if all electrons are replaced by an electron at the centre 

 of their orbit, i. e. in their mean position, there will be a 

 position of equilibrium with all the atoms in a plane. We 

 have not the knowledge which would enable us to say 

 whether this position is stable or not in all cases, but in a 

 symmetrical case it can be shown that stable equilibrium in 

 the plane is possible provided the centres of the orbits 

 marked « in fig. 1 are not very near one or other of the 

 nuclei. 



Therefore, although we are not at present in a position to 

 deduce the stereochemical laws from the model of the mole- 

 cule, there is nothing in the model which is inconsistent 

 with them. 



On this theory, the stereochemical phenomena are due to 

 carbon atoms temporarily functioning as trivalent. 



Possibly, therefore, it may be found that substances of 

 the type 



w 



R» R4 



exist in two forms. 



Some cases of isomerism possibly due to this cause are 

 cited by Stewart, c Stereochemistry,' p. 265 seq. 



A change from a cis to a trans position, or vice versa, is 

 regarded as due to a violent disturbance which ends in 

 one part of the molecule swinging round relative to the 

 other. Such a disturbance could be caused by setting up 

 vibrations in the molecule by means of light or heat, or by 

 the approach of another molecule; and it is to be expected 

 that molecules which can add on to the free valency will be 

 most effective, even if their approach docs not happen to lead 

 to a formation of the addition product. 



7. With regard to optical activity, with our model the 

 groups R x , &c, in a substance CR1R2K3R4 lie in the direction 

 of the angular points of a tetrahedron. If the R's are all 

 different, this tetrahedron will be asymmetric, as in the 

 ordinary theory. In substances of the type 



R '>c=c< R ' 

 R 2 X R 4 



there does not appear to be any reason to expect optical 

 activity unless one or more of the R groups is not restricted 

 to one plane. Even then optical activity could not be found 



