The -C NMR spectra of lupeol and related triterpenes were recorded and all carbon shifts assigned. Their analysis aided in the shift assignment of the strncturally related hopane-like triterpenes.After early work on some tetracarbocyclic triterpenes2s3 there appeared 13C NMR analyses of a-and pamyrinic pentacarbocyclic substance^.^,^ However, except for a report on two hopanes from an oil shale deposit' and the use of a limited number of friedelin shifts for the interpretation of @effects in transdecalin systems6 little is known about the 13C NMR spectroscopy of non-amyrin types of pentacarbocyclic triterpenes. The present communication concerns a 13C NMR study of a large number of lupeol-derived substances and some hopane derivatives. Their shift assignments utilized off-resonance decoupling techniques for the determination of the substitution profile of carbon centers, functionality manipulation causing predictable shift variations, shift assessment utilizing 13C NMR data for carbocyclic systems of known stereochemistry and conformation, especially those of decalins,7.8 perhydr~phenanthrenes,~ diterpenes [e.g. ll0-l3 (the shift assignment of hinokiol (1) is based on that of ferruginol" and of ring A of lano~terol)~] and steroids 14and lanthanide-induced shift measurements.

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.

Sztmmavy.A total carbon shift analysis of several rcprcstmtdivcs of the lal~danc: ditcqcnc family of natural products is prcscnted. 'J'hc shift assignment is l~ascd on thc prior shift designation of some synthctic trans-decalin derivatives.

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