Abstract
The title compounds were prepared optically active, and their variable-temperature circular dichroism (CD) spectra were measured. The ..beta..-axial ketones (1S,3R,4S)-4(a)-(trideuteriomethyl)adamantan-2-one (1) and (1S,3R,4S)-4(a)-methyladamantan-2-one (2) underwent considerable changes in their CD spectra: at -175 /sup 0/C moderately intense (..delta..epsilon approx. 0.5) negative n ..-->.. ..pi..* Cotton effects (CEs) were observed in both polar (EPA) and nonpolar (methylcyclohexane-isopentane) solvents. Those findings contrast with the room temperature n ..-->.. ..pi..* CE signs and magnitudes of 1 and 2: ..delta..epsilon approx. -0.04 in ethyl ether-isopentane-ethanol and ..delta..epsilon approx. +0.02 in methylcyclohexane-isopentane. The ..beta..-equatorial ketones (1S,3R,4R)-4(e)-(trideuteriomethyl)adamantan-2-one and (1S,3R,4R)-4(e)-methyladmantan-2-one gave the expected (+) CEs (..delta..epsilon approx. 1) which are relatively insensitive to temperature and solvent. Comparison of CD/sub 3/ and CH/sub 3/ rotatory strengths indicates that the heavier isotope makes the inherently more dissignate octant contribution.
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