Theory of Molecular Volumes. 981 



Diisopropyl (C 6 H U ). Diisobutyl (C 8 H W ). 



CH 3 CH 3 CH 3 CH 3 



II I I 



CH— CH CH— GH 2 — CH 2 — CH 



II J I 



CH 3 CH 3 CH 3 CH 3 



V normal C 6 H 14 139'93 V normal C 8 H 18 186'26 



V diisopropyl 136-9 V diisobutyl lSo'20 



A ...-3-03 A... -1-06 = 2x0-53 



w-Heptane C 7 H 16 ... 162*92 

 Isoheptane ... 162'34 



A for Iso Group —0*58 



In the case of diisobutyl, the difference ii. volume from 

 ihe normal compound is about twice the contraction for the 

 iso-group. In the case of diisopropyl, the contraction is 

 considerably greater. 



It is reasonable to suppose that in this case the iso-groups 

 are so close that they interfere with each other, but that 

 when two methylene groups intervene the possibility of 

 interaction is diminished. 



So also is this the case with ring compounds. In the 

 ortho position the substituents are so close that they attract 

 each other and so cause diminutions in volume. In the 

 meta- and especially in the para- positions, the substituents 

 cannot so readily interact, as they are further removed and 

 for the most part outside of the range of each other's 

 attractions. 



In both of the above cases by no possibility can the general 

 configuration of the molecule be altered, for in ring com- 

 pounds, which already possess a definite and stable configura- 

 tion, this is seen to be impossible, and in the diiso-paraffins 

 the substituents (CH 3 groups) are symmetrically disposed 

 and balance each other. 



We are left to account for the anomalous behaviour of /3 

 and 7 di-substitution derivatives of the paraffins which show 

 increased contractions, the further they are removed from 

 each other. 



This peculiarity can readily be explained by means of this 

 theory of Residual Affinity which we are considering, and 

 which has been so fruitful in the hands of Thiele under the 

 name of Partial Valency. 



We must suppose that the attractive force between the 

 Phil. Mag. S. 6. Vol. 27. No. 162. June 1914. 3 T 



