Hans von Walter

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1bis research initially set out to study the reaction kinetics of 2-cyclohexen-1-ol. This molecule, when undergoing an acid-catalyzed dehydration with 84.0% w/w sulfuric acid, was expected to follow the same pathway found in the later steps of the acid-catalyzed dehydration of cyclohexanol, namely, the formation of an allylic carbocation. Analysis using UV-Vis spectroscopy, however, showed that this was not the case. The primary absorption band in the UV-Vis spectrum of the dehydration of cyclohexanol, an allylic carbocation having A.max at about 300 nm, was not visible in the UV-Vis spectrum of2-cyclohexen-1-ol. Instead, a strong absorption band at 380 nm (indicative of a dienylic carbocation) was immediately formed, followed by its gradual decrease. Consequently, what was initially a study of the analogous relationship between the kinetics and mechanism of the acid-catalyzed dehydrations of cyclohexanol and 2-cyclohexen-1-ol turned into a focus studying the mechanism ofthe 2- cyclohexen-1-ol reaction. Further experiments were conducted in which the amounts of sulfuric acid and 2-cyclohexen-1-ol were varied. It was discovered that at low acidity, a prominent absorption band was observed at 260 nm, attributed to 1 ,3-cyclohexadiene. At high acidities, the prominent band was observed at 380 nm and corresponded to a dienylic carbocation. These experiments lead to the proposal that a concerted elimination step was responsible for the rapid formation ofthe dienylic carbocation.

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