Thiele’s theory of partial valency

By means of such assumptions, Werner was able to account for certain previously unexplained phenomena, such as the formation of tetrahydro-terephthalic acid by reduction of A dihydroterephthalic acid. It must be admitted, however, that this so-called 1,4 addition to conjugated double bonds was later explained in a more satisfactory manner by Johannes Thiele s theory of partial valences. 

Cyclooctatetraene (I) was first prepared in 1911 [1], Its properties came as a great surprise to most organic chemists at the time conditioned by the knowledge of the properties of a cyclic system of formally alternate single and double bonds as found in benzene, and by Thiele s theory of partial valencies, and notwithstanding Bamberger s concept of hexacentric systems,(see Chapter I), they had expected it to be like benzene in its properties. But like benzene it was not. 

The anomalous behaviour of butadiene on halogenation has been recognized for some time. It would be expected that the addition of bromine across one of the double bonds would produce only the molecule CH2BrCHBr CH=CH2. However, in addition to the 1,2-dibromo, compound there is a considerable yield of the 1,4-dibromo compound CH2Br—CH=CH—CH2Br, which contains a double bond in the 2,3 position. In order to explain this behaviour, Thiele proposed a theory of partial valencies. In this theory the second link in a double bond does not fully neutralize the affinity of the two carbon atoms so that they are left with a residual affinity In a system of alternate double and single bonds, the residual affinities of the inner atoms combine across the single bonds whilst those of the outer atoms remain free to attract other atoms. Thiele s formula for butadiene was therefore... 

Early depictions relevant to the development of the electronic theory of organic chemistry A) representation of the reaction between 1,3-butadiene and Br2, in the manner of Robinson, depicting partial bonds and polarities B) the "birth of the Robinson-Kemack curly arrows representing partial valences in 1,3-butadiene C) application by Robinson of curly arrows toward the explanation of meta substitution in nitroso benzene D) early representations by Thiele and others of the equivalence of all bonds in benzene E) Robinson s 1925 representation of benzene... 

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