Discussion
The methyl carbon of the acetone-d6 appears in the 13C-NMR as :
Answer: C
The CD3 carbon gives a septet with intensities 1 : 3 : 6 : 7 : 6 : 3 : 1.
In acetone-d6 each methyl carbon carries three deuterium atoms, and deuterium has spin I = 1. The number of lines is 2nI + 1:
\[ 2nI + 1 = 2(3)(1) + 1 = 7 \]
The intensities are not binomial, because each deuterium has three equally likely orientations (+1, 0, −1), not two. One D gives 1:1:1; adding a second gives 1:2:3:2:1; adding the third gives 1:3:6:7:6:3:1, the familiar pattern of the CDCl3 triplet extended.
1:6:15:20:15:6:1 is the binomial septet from six spin-1/2 nuclei, the pattern of a proton next to two CH3 groups. The quintet is the pattern for two deuteriums (a CD2 group), and a sextet does not arise from three spin-1 nuclei.
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