Adamantanones octant contributions

The chirality of (15 )-2-adamantanone-4-13C (87) and (lS )-2,4-adamantanedione-4-13C (88) is solely due to 13C substitution. Since the 13C ring carbon of 87 is located in a positive octant, from the negative Cotton effect of 87, it follows that 13 C makes a smaller contribution than 12C. Diketone 88 exhibits three CD bonds with remarkably large amplitudes, which were attributed to different n - tt transitions195. 

The ring carbons of the rra/u-4-ketodecalin (e) lie in the same back octants as the tratis-1 -decalone (a), so these perturbers should sum to a (-) contribution to the CD. The only difference between (e) and (a) is the /3-axial methyl in the former, which is known from earlier work on adamantanones (see preceding section) to be a weak dissignate perturber (in this case a weak (+) contributor). The observed negative CE of (e) is only slightly smaller than that of (a). 

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