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A carbon-shift analysis of labdanic diterpenes of the manool, agathic acid, and sciadin types is presented. The C-12 and C-20 configurations of sciadin have been determined and the structure of potamogetonin has been revised. 'Dedicated to Professor Edgar Lederer on the occasion of his seventy-fifth birthday. 2Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Naturally Occurring Substances, LXXXI.

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Experimental results and a theoretical model are presented which give strong evidence that the ratio β/L2μM is a constant for a large class of disubstituted conjugated hydrocarbons, β is the second-order polarizability, μM the mesomeric dipole moment, and L the length of the hydrocarbon chain.

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The mechanism of the oxidation of alcohols by silver carbonate on Celite was thoroughly investigated to ascertain the nature of the transition state and the possible intervention of reaction intermediates. Kinetic, stereochemical, and isotopic labeling techniques were used to differentiate among the various theoretically plausible mechanistic alternatives. The effects of surface adsorption and solvent composition on the outcome of the reaction were also studied. The data were consistent with a concerted process for which a model is proposed.

Silver carbonate on Celite in neutral media effects selective oxidative coupling of hindered phenols giving the corresponding dipheno-and stilbenequinones in high yields. Bis phenols obtained by reduction of these quiñones were also oxidized by silver carbonate. When coupling was not possible due to steric factors, the stable phenoxy radicals were isolated quantitatively. Hydroquinones and pyrocatechols gave the corresponding p-and oquinones in excellent yields. Oxidation of p-hydroxydiphenylamine and o-aminophenol gave the corresponding monoanil and phenoxazone, respectively.

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