A. Sementsov
Lafayette College Easton, Pennsylvania
Who Proposed the Dewar Formula of Benzene?
Authors who attribute to Dewar the bridged formula of benzene,
bicyclo [2:2 :01,4]hexadiene, refer usually to his paper presented to the Royal Society of Edinburg in 1867.' In this paper Dewar describes his experiments aimed to elicit "Kekule's original and elegant speculations on the structure of benzol and its derivatives." In connection with this subject, he brought before the Society a simple mechanical arrangement adapted to illustrate structure in the nonsaturated hydrocarbons. To show the ease with which this instrument can represent the same hydrocarbon in different ways, he presented the seven models of benzene shown in the figure. He presented, in addition to Kekule's ideas and the bridged formula now attributed to Dewar, formulas containing three- four- and five-membered rings, some of which are bizarre. We can see, therefore, that Dewar did not propose the bicyclic formula nor did he propose the other six formulas. The bridged formula was first proposed by two German chemists. I n 1868, Staedeler2 proposed the following: D ~ w n r t J., , Pvoc. Roy. Soc. Edinburgh, 6 , 82 (1867). 'STAEDELER, G., J. prakt. Chem., 103, 105 (1868). a J ~E., But. ~ Soe. Chim. ~ F ~~a n c e[2], ~ 4, 241 ~ 9, 346 (1868). OTTO, R.,A N D OSTRUM,H., J. prakt. Chem., 102, 27 Ann., 141, 93 (1867). 6 WICHELHAUS. H.. Rer. 2.197 11869).
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As an argument in favor of this formula, he adduced the mistaken information that mono- and pentachlorobenzene exist in two isomeric forms. He did not give reference to, hut probably derived his information from, papers of Jungfleisch3 and Otto and O ~ t r u m . ~ The last authors claimed that they separated two suhstances of the formula CsHCIS with melting ranges 215-220" and 79-85' respectively. The ranges suggest that they had mixtures and not the individual suhstances. The next year Wichelhauss suggested this formula: CH CH CH
He proceeded from the idea that benzene is formed by the polymerization of acetylene in the following way:
with the intermediate formation of cyclobutadiene. Volume 43,
Number 3, March 1966 / 151
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