ORGANIC CHEMISTRY 17 



The angle assumed by Baeyer between the valency directions 

 (109*5°) is the angle at the centre of a regular tetrahedron 

 subtended by a side and it is now suggested that the tetra- 

 hedron representing the carbon atom is regular only when four 

 similar groups are attached. In the polymethylenes, where 

 two carbons and two hydrogen atoms are attached to the 

 carbon atom, account has to be taken of the relative sizes of 

 the atoms, and the corresponding effect on the regularity of the 

 tetrahedon. If it is assumed that the central carbon atom is 

 a sphere touched by four spheres representing the hydrogen 

 and other carbon atoms, these being in contact with each other 

 and their volumes proportional to the atomic volumes of carbon 

 and hydrogen, by joining the centres an irregular tetrahedron 

 is obtained. It can be shown that in this tetrahedron the angle 

 between the carbon to carbon valency directions is 115*3°. 

 Using this angle the relative stability of the various rings as 

 shown by the strain present is in accord with the thermo- 

 chemical results. 



In order to test his assumptions the author proposes to 

 study quantitatively the ease of formation of the various 

 methylene rings. In order to do this reactions are being inves- 

 tigated in which one or more side reactions can compete with 

 ring formation. In these circumstances the relative amounts 

 of products formed under standard conditions will be a measure 

 of the ease of ring formation. 



The example chosen is the removal of hydrobromic acid 

 from a-bromo-glutaric, a-bromo-adipic, etc., acids. The ring 

 formation and the competing reactions in these cases will be : 



CH Br • COgH 



I /CH • CO2H 



CH2 -> CH2< I and 



1 XH • COaH 



CHj • CO2H 



CH(OH) • CO2H CH • CO2H 



II 



CH2 and CH 



I I 



CH2 * CO2H CHa • CO,H 



CH2 • CH Br • CO2H CH2 - CH • CO2H 

 I -^11 and 



CH2 * CH, • CO2H CH2 - CH • CO2H 



CHj • CH(OH) • CO2H CH : CH • COgH 



I and I 



CH, • CH2 • CO2H CHa • CHg * COaH 

 2 



