B.— CHEMISTRY. 40 



It is, therefore, not a conjugated system in the sense that butadiene is 

 a conjugated system. 



We have now succeeded in isolating cis-hexatriene, and are studying 

 the action of bromine on it. If, as is to be anticipated, the addition takes 

 place in the 1 : 6 positions, direct evidence will be available in favour of 

 the electronic hypothesis. The work is, however, exceedingly difficult 

 because, unlike those of the trans series, the cis compounds are liquids 

 and therefore dilficult to identify. Moreover, they are unstable and 

 readily polymerise to resins on keeping. There is no doubt, however, 

 that these difficulties will be overcome. 



In the same way the Thomson^ formula for benzene provides an 

 expression for the intermediate state as postulated by Kekule, and renders 

 the so-called centric formula, which is meaningless, now unnecessary. 



I 



There can be no question that the distribution of electrons among the 

 carbon atoms and other atoms of organic molecules must determine the 

 reactions of the complexes involved, and future research will no doubt 

 lead to an advance in our knowledge concerning the causes which promote 

 or retard this distribution. 



The ductility of the carbon to carbon bonds which have now been 

 clearly demonstrated enables us to impart strains to certain parts of an 

 organic molecule at will, and it is reasonable to assume that such strain 

 when once set up will be shared as far as possible equally by all the atoms 

 of the system involved. If this distribution is, as Robinson postulates, 

 effected by a restricted flow * of electrons from one atom to another in 

 the molecule, we have, at any rate, a definite picture of the process which 

 the mind can grasp ; and if the distribution leads ultimatelj^— as is to 

 be surmised— to the establishment of polar characteristics at different 

 parts of the molecule, which will determine reactivity at those points, we 

 are in a fair way to reconcile the views of various contending schools and 

 to reach a general hypothesis acceptable to all chemists, and which may 

 even satisfy the physicists. It seems that, despite the organic chemist's 

 proneness and ability to distort the molecules with which he deals, nature 

 has provided a means by which a certain degree of molecular equilibrium 

 can be attained. Nevertheless it will be by the investigation of the 

 conditions leading to the setting up of strain and of the effect produced 



' See also H. Kaufimann {Die Valenzlehre, 1911, p. 539). 



2 Robinson considers that an electron may leave its 'moormga' on one of the 

 atoms which holds it but never on both. 



1926 E 



