Abstract

The molecular proportionality between C₆ and C₇ isomers reported recently (F. D. Mango, Geochim. Cosmochim. Acta, 2000, 64, 1265; ) is probably the strongest evidence for catalysis yet published. It implicates two cyclopropane-like precursors, [S₆] and [S₇] (where S denotes any substrate), of similar structures, each yielding three isomers along similar kinetic pathways: This view is supported here by the carbon isotope ratios of these isomers in 36 oils from Western Canada (M. J. Whiticar and L. R. Snowdon, Org. Geochem., 1999, 30, 1127; ). They exhibit strong correlations in δ¹³C, consistent with their being formed in triads through isotopically indistinguishable precursors. These results add significantly to the growing body of evidence supporting catalysis.