Optical Isomerism, and the Ring- Electron, 



485 



The evidence at present available does not justify a 

 decisive verdict as between the two possible arrangements 



and 



for the electron pair.' It may be that both are possible, with 

 corresponding differences in the optical and magnetic 

 properties of the compound. On tlie basis of the latter con- 

 figuration, a large number of isomerides may exist in accord- 

 ance with the suggestion of Garner, referred to above. w< The 

 electrons rotating in pairs around the four carbon valencies 

 may possess either clockwise or anti-clockwise rotation with 

 respect to the central carbon atom. On the assumption that 

 two of these pairs of electrons rotate in a clockwise and two 

 in an anti-clockwise direction, it is possible to deduce that 

 eight isomerides of cinnamic acid may exist.'"' If the clock- 

 wise rotation of the electron gives a north-seeking character 

 to the valency and the anti-clockwise rotation a south- 

 seeking character, isomerides may exist which may be 

 represented graphically as below 



Bi 



E 



S N 



N S 



\ / 



C 



/ \ 



S N 



N S 



R 2 Ri 



\ / 



S N 



N S 



\ / 



C 



S N 



N IS 



R ? 



% 



/ 



R 4 



R 



The existence of the isomeric compounds suggested by 

 Garner depends upon the somewhat arbitrary assumption 

 that two of the pairs of electrons are rotating in a clockwise 

 sense, and the other two in an anti-clockwise sense as viewed 

 from the carbon atom. In a three-dimensional model the 

 four valencies may be supposed directed towards the corners 

 of a regular tetrahedron. It will then be observed that 

 Garner's assumption implies that the valency electrons in 

 such a compound confer upon it paramagnetic properties, 

 since the suggested arrangement of electrons would have 



