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首页> 外文期刊>Chemistry: A European journal >Chiroptical Properties of cisoid Enones from Circular Dicroism (CD) and Anisotropic Circular Dichroism (ACD) Spectroscopy
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Chiroptical Properties of cisoid Enones from Circular Dicroism (CD) and Anisotropic Circular Dichroism (ACD) Spectroscopy

机译：圆二色性（CD）和各向异性圆二色性（ACD）光谱测定的类固醇烯酮的手性

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摘要

Substituted cisoid 4-en-6-one steroids with isotropically distributed and partially oriented molecules were analyzed by circul dichroism (CD) and anisotropic ciruclar dichrosim (ACD) spectrocopy, respectively. CD and ACD data supllement their respective phenomenolgical informatin. For a series of C3-substituted enones 1 to 7, the difference of CD(#delta##epsilon#) and ACD (#DELTA##epsilon#~A) values, that is, #DELTA##epsilon#-#DELTA##epsilon#~A, vary in the n-#pi#~* transition region in the same direction, independently of the nature and position (3#alpha# or 3#beta#) of the substituent. For 7#alpha#-bromo-substitued enones 5 and 6 the sign of the n-#pi#~-* CD band is opposite to that predicted by the enone helicity rule. The ACD data indicate that this behavior is a consequence of the effect of vibronic coupling caused by the 7#alpha#-bromo substituent. In contrast to the results obtaiend for the series of C7-unsubstituted compounds 1 to 47, the intensity of the CD bands for 5 and 6 is determined by the vibrational progressions of a different symmetry. Therefore, the helicity rule must fail in both cases because the rule can only be applied to those vibrational transitions for which the rule was developed. The sign of the coordiantes #DELTA##epsilon#_(ii)~*, estimated from the ACD data, yields additional stereochemical information that cannot be obtained from the CD data alone. The CD and ACD spectra in the region of the #pi#-#pi#~* transition vary for enones 1 to 4 in a different fashion and indicate dependence upon spatial orientation (3#alpha# or 3#beta#) of substitutents. This dependence may lead to the possiblity of extracting additional stereochemical information from the ACD spectra. Furthermore, the experimental findings indicate that the second CD band located at about 220 nm belongs to a forbidden transition and not to an allowed #pi#-~pi#~- transition.
机译：各向同性分布和部分定向的分子的取代的类固醇4-en-6-one类固醇分别通过循环二色性（CD）和各向异性的ciruclar dichrosim（ACD）光谱分析。 CD和ACD数据补充了它们各自的现象学信息。对于一系列C3取代的烯酮1至7，CD（＃delta ## epsilon＃）和ACD（＃DELTA ## epsilon＃〜A）值的差，即＃DELTA ## epsilon＃-＃DELTA ε在相同的方向上在n-π过渡区域中变化，而与取代基的性质和位置（3＃alpha＃或3＃beta＃）无关。对于7＃alpha＃-溴取代的烯酮5和6，n-＃pi＃〜-* CD谱带的符号与烯酮螺旋度规则预测的符号相反。 ACD数据表明，此行为是由7＃α＃-溴取代基引起的振动耦合效应的结果。与获得一系列C7未取代化合物1至47的结果相反，5和6的CD谱带的强度由不同对称的振动进程确定。因此，螺旋规则在这两种情况下都必须失败，因为该规则仅适用于为其制定规则的那些振动过渡。从ACD数据估计的coordiantes＃DELTA＃epsilon #_（ii）〜*的符号会产生其他立体化学信息，这些信息不能仅从CD数据中获得。 #pi＃-＃pi＃〜*跃迁区域中的CD和ACD光谱对于烯酮1至4以不同的方式变化，并表明对取代基的空间取向（3＃alpha＃或3＃beta＃）的依赖性。这种依赖性可能导致从ACD光谱中提取其他立体化学信息的可能性。此外，实验结果表明，位于约220 nm处的第二个CD谱带属于禁止的跃迁，而不属于允许的＃pi＃-〜pi＃-跃迁。

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