Conant and

Remarkably accurate experimental results have been obtained, also by Kistia-kowsky (Conant and Kistiakowsky, 1937), which permit indirect calculation of the enthalpy change of this isomerization AThe enthalpy diagram for isomcn/atioii of 2-butciic is given in Fig. 5-.5. We shall use TINKER and PCMODEL U) (ind the length of each arrow in Fig. 5-5. We shall also use the PCMODEL GUI. a powerful tool for tile construetion. 

If has long been known that the enthalpy of hydrogenalion of benzene (49.8 kcal moU Conant and Kistiakowsky, 1937) is not the same as three times the enthalpy of hydrogenation of cyclohexene (3 x 28.6 kcal moU ). Evidently, the double bonds that w e write in the Kekule structure of benzene... 

Submitted by Kurt H. Meyer. Checked by J. B. Conant and W. C. Boyd. 

Submitted by Arthur Larworth and Wilson Baker. Checked by J. D. Conant and Mildred Evans. 

Mechanistic understanding of azo coupling reactions was initiated by Conant and Peterson (1930) and Wistar and Bartlett (1941) in two pioneering studies done at Harvard University (see Sec. 12.7). 

It is well known that the rates of all azo coupling reactions in aqueous or partly aqueous solutions are highly dependent on acidity. Conant and Peterson (1930) made the first quantitative investigation of this problem. They demonstrated that the rate of coupling of a series of naphtholsulfonic acids is proportional to [OH-] in the range pH 4.50-9.15. They concluded that the substitution proper is preceded by an acid-base equilibrium in one of the two reactants, which was assumed to be the equilibrium between the diazohydroxide and the diazonium ion, in other words, that the reacting equilibrium forms are the undissociated naphthol and the diazohydroxide. 

Conant and Peterson123 made the first kinetic study of the coupling of diazonium ions with aromatics, and measured the rates of reaction of diazotised aniline and its 2-MeO, 4-Me, 4-Br and 4-S03H derivatives with the sodium salts of 4-hydroxybenzenesulphonic acid, 2-naphthol-3,6-disulphonic acid, 1-naphthol-3,8-disulphonic acid, and l-naphthol-4-sulphonic acid. The reaction was second-order, viz. 

Dibenzoylcyclopropane has been prepared by the method described here and previously by Conant and Lutz. Both procedures use 1,3-dibenzoyIpropane as the reactant. The present procedure is accomi)lishcd in one step under very mild cojiditions and in nearly (iiiaiititative yield. Tlie method of... 

Conant and Lutz is a two-step process involving initial di-bromination of the diketone followed by ring closure with zinc and sodium iodide. The overall yield of traws-l,2-dibenzoyl-cyclopropane is approximately 15%. The submitters have extended the described method to the preparation of other frans-1,2-diaroylcyclopropanes, namely acidic hydrogens on both a-carbons. A probable mechanism for this transformation is as follows ... 

---