Centro Universitario de la Defensa, Academia General Militar, 50090 Zaragoza, Spain.
Chemistry. 2013 May 3;19(19):6044-51. doi: 10.1002/chem.201204197. Epub 2013 Mar 5.
Achiral compounds 4-methoxy-4-(p-methoxyphenyl)cyclohexanoneethylene ketal (2), 4-hydroxy-4-(p-methoxy phenyl)cyclohexanoneethylene ketal (3), and 3,5-dimethyl-4-nitropyrazole (4) crystallized in chiral structures and the samples showed an enantiomeric excess. We have determined the absolute structures of these compounds by using X-ray diffraction with copper radiation at low temperatures. Moreover, we have also established the prevalent absolute structures in these samples, by comparing their calculated and solid-state vibrational circular dichroism (VCD) spectra. The consistency of this method was confirmed by using (R,R)-2,8-diiodo-4,10-dimethyl-6 H,12H-5,11-methano-dibenzo[b,f][1,5]diazocine, Tröger's base, (R,R)-1, as a chiral compound of known absolute configuration.
非手性化合物 4-甲氧基-4-(对甲氧基苯基)环己酮缩乙二醇(2)、4-羟基-4-(对甲氧基苯基)环己酮缩乙二醇(3)和 3,5-二甲基-4-硝基吡唑(4)结晶为手性结构，样品表现出对映体过量。我们使用低温下的铜辐射 X 射线衍射确定了这些化合物的绝对结构。此外，我们还通过比较计算和固态振动圆二色性(VCD)光谱，确定了这些样品中占主导地位的绝对结构。使用(R,R)-2,8-二碘-4,10-二甲基-6H,12H-5,11-甲撑二苯并[b,f][1,5]二氮杂环辛烷、特罗格碱和(R,R)-1(一种已知绝对构型的手性化合物)作为手性化合物，验证了该方法的一致性。
