| Popis: |
Coalescence phenomena have been observed in the NMR spectra of a variety of 7-substituted 1,3,5-cycloheptatrienes upon varying temperature and/or solvent. Using two different methods, the energy of activation of the process responsible for coalescence has been determined. Within a group of structurally similar para-substituted phenyl sulphides a linear relation has been found between the energy of activation and the acidity constant of the corresponding benzenethiol, suggesting the occurrence of ion pairs. The relatively low energy of activation for the phenyl sulphides, when compared with the values of the phenyl sulphones, may result from the structure of the intermediate ion pairs. In addition to the above, a different exchange process between cycloheptatrienyl sulphides and tropylium salt via sulphonium ions has been observed. |
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