| Abstract: | A series of 3-(aryl)-3,5,5-trimethylcyclohexanones and their analogous cis and trans tertiary methyl alcohols were prepared and characterized by detailed proton NMR studies. These studies included an extensive characterization of stereochemistry by means of lanthanide-induced shifts (LIS), primarily using Eu(FOD)₃. A method for the regression analysis of the concentration dependence of the LIS of these substrates was developed and used to derive the proton chemical shifts (δ₀) in the absence of lanthanide shift reagent (LSR). These studies provided a system for probing shift reagent complexation of substrates having two sites of greatly differing basicities; a carbonyl or hydroxy function vs. an aryloxy moiety. LIS data was also used to examine the possible mechanisms involved in the aryl ring bond rotation processes in the ketone and cis alcohols. The results of these studies were consistent with the existence of biased mobile equilibria between two chair-like conformers. The extent of biasing is much greater in the ketones and cis alcohols than in the trans alcohols. The conformations of these systems found via LIS are consistent with: (1) an axially disposed aryl substituent in the 3-aryl ketones and the derived cis alcohols, with the hydroxy function in the latter compounds also enjoying an axial disposition. For the trans alcohols the aryl substituent is equatorially disposed with the hydroxy moiety being axial; (ii) a flattened chair form of the cyclohexene ring caused by syn-axial compression ("reflex effect") between the two large axial substituents, at C-3 and C-5. ... |
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