OPTICAL-ACTIVITY OF LOW-SYMMETRY KETONES IN ABSORPTION AND EMISSION
OPTICAL-ACTIVITY OF LOW-SYMMETRY KETONES IN ABSORPTION AND EMISSION
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DOI：
10.1021/ja00424a034
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发表时间：
1976-01-01
影响因子：
15
通讯作者：
CLOSS, LE
中科院分区：
文献类型：
--
作者：
DEKKERS, HPJM;CLOSS, LE
通过吸收和发射研究了一系列酮的 n-** 跃迁中的光学活性。对于许多酮，实验 CD 和 CPL 光谱的比较揭示了明显的差异：积分光学活性的大小和带形状在吸收和发射方面可能完全不同。本文阐述了这些现象之间的关系。吸收和荧光的旋转强度值（对于某些化合物高达符号）之间通常存在巨大差异，这表明酮的**状态相对于其基态存在很大的扭曲。另一方面，从一般原理来看，Rabs/Rem 的比率为负值需要 CD 或 CPL 曲线中的符号发生变化，即会导致双符号 Cotton 效应。为了更好地了解观察到的现象，构建了一个模型来预测 CD 和 CPL 的定性带形式。基于基态和激发态之间平衡几何结构的巨大变化，该模型利用了围绕法向坐标空间点的电子旋转强度的扩展，在这些点上，特定电子振动跃迁的弗兰克-康登重叠达到峰值。当假设旋转强度与一个法向坐标之间存在线性关系时，可以成功解释所研究的酮的 CD 和 CPL 的观察到的带形状。除了更好地理解双符号科顿效应的起源之外，这项研究得出的结论是，只要适当考虑激发态的合理作用，酮的 n-* 7r* 跃迁中的光学活性仍然可以用莫菲特和莫斯科维茨相对简单的理论来理解。
The optical activity in the n—** transition of a series of ketones is studied in absorption and emission. For a num-ber of ketones the comparison of the experimental CD and CPL spectra reveals marked differences: both the magnitude of the integrated opticalactivity and the band shape may be utterly different in absorption and emission. In this paper a relation is laid between these phenomena. The often large discrepancy between the value of the rotational strength in absorption and fluorescence (for some compounds up to sign) points to a large distortionof the** state of ketones with respect to their ground state. On theother hand it is shown from general principles that a negative value of the ratio Rabs/Rem requires a change of sign ineither the CD or the CPL curve, ie, can cause a bisignate Cotton effect. To get a better insight in the ob-served phenomena, a model is constructed to predict the qualitative band forms of the CD and CPL. Based on the large shift in equilibrium geometrybetween ground and excited state, the model makes use of an expansion of the electronic rotational strength about those points of normal coordinate space where the Franck-Condon overlap for a particular vibronic transition is peaked. When a linear relationship between the rotational strength and one normal coordinate is assumed, the observed band shapes of CD and CPL of the ketones studied can be successfully explained. In addition to a better understanding of the origins of bisignate Cotton effects, this study leads to the conclusion that the optical activity in the n—* 7r* transition of ketones still can be understood with the relatively simple theoryof Moffitt and Moscowitz, provided proper allowance is made for a legitimate role of the excited state.