Diamagnetic susceptibilities and susceptibility exaltations of some 7-substituted cycloheptatrienes

The diamagnetic susceptibilities of several 7-substituted cycloheptatrienes have been measured and used in conjunction with estimated values of their susceptibilities (Haberditzl increment system) to obtain the susceptibility exaltations of these compounds. These exaltations were found to be very large and to vary as a function of the size of the C 7 substituent. There was no apparent correlation of the exaltation of a compound with the electronic properties of its substituent. The effect of a substituent on the susceptibility exaltation is interpreted in terms of conformational changes in the seven-membered ring. The magnitude of the susceptibility exaltations of these cycloheptatrienes, for example 7-tert-butylcycloheptatriene (Λ = 14.8), in comparison to that of benzene (Λ = 13.7) would suggest that the presence of an induced diamagnetic ring current is not a good criterion of its aromaticity.