980 Mr. Gervaise Le Bas on the 



These results show : — 



(a) That there is always a contraction when the substi- 

 tuents are in the ortho- or 1:2 position ; that is, when they 

 are nearest to each other. 



This is apparently a regularity similar to that involved in 

 substitutions in the 1 : 2 position in open-chain compounds, 

 although the influence o£ residual affinity must be less, owing 

 to partial saturation of the substituents. In the above table 

 the contractions are <2'0. In the case of nitrotoluene the 

 contraction is greater, —2*6, probably owing to the great 

 influence of the N0 2 group. 



The explanation to follow is not affected by considerations 

 connected with the spatial arrangement of the atoms and 

 groups. The two groups in the above table are considered 

 to be on the same side of the ring. It would be interesting 

 to know how the two geometrical isomerides differ as regards 

 volume. 



{b) Meta 1 : 3 substitutions show small contractions, and 

 para 1 : 4, which are normal, none at all. 



j)-Xylene. Dimethyl Resorcin. 



^C-CH 3vC6H4 g96 ^ C \ 0CH3 VC 6 H 4 89.6 



CH CH 2CH3 5^2 CH CH k 2 CH 3 66i> 



CH OH SA ' V - 140 ' 8 CH CH ^.V. 156,2 



Oc— CH. C™OCH 3 



(c) In Ring Compounds the contractions diminish as the 

 substituents are removed the further away from each other. 



(C) Explanation of Constitutive Effects. 



Having pointed out two important constitutive effects in 

 open-chain and closed-chain compounds, we attempt their 

 explanation. The following differences to be observed in 

 different cases will assist in the elucidation of the problem. 



In open-chain compounds they increase. This is an 

 important distinction, and since the result in the case of 

 ring compounds is what we should expect, the peculiarity 

 in the case of open-chain compounds calls for special 

 explanation. 



One or two cases occur in the latter which follow the 

 same rule as for ring compounds, and this will help us at 

 arriving at a solution of the difficulty. 



