116 Dr. Carnelley on the Influence of Atomic Arrangement 



arrangement is asymmetrical ; i. e. if we imagine the para- 

 compound to be suspended from a point in the centre of the 

 benzine ring, then the molecule would balance in any position, 

 whilst this would not be the case with the ortho- and meta- 

 compounds. Or, in other words, the centre of gravity of the 

 molecule of the para-compounds corresponds more nearly with 

 the centre of figure of the molecule than is the case with the 

 ortho- and meta-compounds. This fact led me to conclude 

 that a similar rule might hold good, not only with the primary 

 derivatives of benzene, but also in the case of all isomeric 

 compounds of carbon ; and this appears to be true in a very 

 large number of instances. I have therefore ventured to con- 

 clude, " That of two or more isomeric compounds, those whose 

 atoms are the MORE SYMMETRICALLY and the MORE COMPACTLY 

 arranged melt higher than those in which the atomic arrange- 

 ment is asymmetrical or in the form of long chains''''*. 



After working out this subject at some length, I noticed 

 that Mr. Henry Watts had already observed, in the third Sup- 

 plement of his well-known ' Dictionary of Chemistry,' that 

 " the more symmetrical the constitution of a benzene deriva- 

 tive, the greater is the resistance which it offers to the passage 

 from the solid to the liquid state," or, in other words, the 

 higher the melting-point. Subsequently, however, in a note 

 to a paper by Neville and Winther ( Journ. Chem. Soc. xxxvii. 

 p. 450), Mr. Watts emphatically says that he intended this 

 rule to apply only and solely to the derivatives of benzene 

 containing but six atoms of carbon ; whilst I believe that it 

 holds good, with a very few exceptions, in the case of all car- 

 bon compounds whatever. 



Let us now illustrate this rule by a number of examples 

 taken almost at random. In the following tables the com- 

 pounds are generally, though not always, arranged in the order 

 of symmetry, those to the left being the most symmetrical. 

 In the case where two compounds are equally symmetrical, 

 that which is most compact is placed to the left. 



I. 



Tetraniethyl methane. Normal pentane. Dimethylethvl methane. 



CH 3 I 



l 



CH 3 — C— CHj 



CH 3 



m.p.= -20. 



CH 3 .CH 2 .CH 2 .CH 2 .CH 3 



Liquid. 



CH 3X /CH 2 .CH 3 

 CH/ h 



Liquid. 



* In the examples given below of this and of all the rule9 stated subse- 

 quently, the exceptions are in every case marked with an asterisk. 



