40 SECTIONAL ADDRESSES 



the scope of the rule. An effective atomic number corresponding with 

 the succeeding inert gas is, however, clearly not a necessary condition for 

 a tetrahedral octet, as is shown, for example, by the tetrahedral configura- 

 tion of the permanganate ion. 



Where the presence of four-electron links is to be inferred, the rule 

 similarly correctly indicates the configuration. Thus carbon dioxide, 

 according to the rule, should be a linear compound, and its infra-red 

 spectrum and zero di-pole moment indicate that it has in fact this 

 configuration. 



The value of the stereochemical indications given by the octet rule is 

 well illustrated by a comparison of some of the compounds of sulphur 

 with compounds to which, until comparatively recently, chemists were 

 in the habit of attributing similar constitutions. Thus, application of the 

 rule shows at once that sulphur dioxide will not correspond in configuration 

 with carbon dioxide. In sulphur dioxide one oxygen atom, according to 



Sulphur dioxide. Sulphinic Ester. 



Fig. 3. 



the octet rule, must be bound by a four-electron link, the other by a 

 two-electron link to the sulphur. The tridimensional octet indicates that 

 sulphur dioxide must then have an angular configuration with an angle 

 between the lines joining the sulphur and the oxygen centres which, if 

 the tetrahedron were regular, would be 125-5° ; ^^id, as is well known, 

 the large molecular di-pole moment and the indications of the infra-red 

 spectrum of sulphur dioxide show that its configuration must in fact 

 be angular. Again, the analogy of the sulphite ion in configuration to 

 the chlorate ion, both of which according to the results of X-ray examina- 

 tion are pyramidal structures, and its difference from the planar carbonate 

 ion is very clearly shown and on the basis of the octet rule could easily 

 have been predicted. 



I believe the highly interesting discovery by Phillips, some seven or 

 eight years ago, of the molecular dissymmetry of the sulphinic esters 

 came as a complete surprise to chemists, for the common practice had 

 been to assign to these compounds a constitution analogous to that 

 attributed to the carboxylic esters. In a similar way the sulphoxides were 

 generally given formula5 corresponding with those of the ketones until 

 Kenyon and Phillips showed that sulphoxides of appropriate constitution 

 could be resolved into optical antimers. 



