dichroism measurements of (2S)-2-methyl-d/sub 3/-2-methylcyclohexanone (2) and (2S)-2-methyl-/sup 13/C-2-methylcyclohexanone (4), quantitative values for the conformational isotope effect are obtained. The chair conformation with the heavier isotope in the equatorial position is found to be energetically preferred by 3,4 and 1.5 cal/mol for 3 and 4, respectively, and empirical force-field calculations
                                    通过(2S)-2-甲基-d/sub 3/-
2-甲基环己酮(2)和(2S)-2-甲基-/sup 13/C-
2-甲基环己酮(4)的变温圆二色性测量,获得构象同位素效应的定量值。发现在赤道位置具有较重同位素的椅子构象分别为 3,4 和 1.5 cal/mol 3 和 4,并且经验力场计算定性地证实了这一观点。与 CH/sub 3/ 相比,CD/sub 3/ 和 /sup 13/CH/sub 3/ 组充当较弱的八分仪干扰器。