Intermolecular charge-transfer (CT) complexes between a wide range of carbonyl compounds and iodine monochloride were spectroscopically studied in the UV–visible region. Equilibrium constants and Gibbs energy changes of 1:1 charge transfer complexes were determined in CCl4 solution. The ICl basicity scale in CCl4 of the set of carbonyl derivatives
included in this study is well correlated with the I2
basicity scale in the same solvent. Ab initio calculations
at HF/LANL2DZ* and MP2(full)/LANL2DZ* were carried out in order to clarify the structures of these CT complexes. Two different conformations, depending on the characteristics of the substituents, may be found. In
one of them the ICl moiety lies in the plane of the carbonyl group, in the other the ICl subunit is perpendicular
to the CO group. The perpendicular complexes are favored by bulky substituents for which the HOMO has a clear π-character.
Both kinds of complexes can be spectroscopically distinguished since they present the CT absorption at different
wavelengths. In both kinds of complexes the carbonyl–ICl interaction is essentially electrostatic. The substituent
effects were analyzed through the use of the Taft–Topsom model. Experimental data in solution and theoretical estimates were
found to follow a good linear relationship.
在紫外-可见光区域,对一系列羰基化合物与
氯化
碘之间的分子间电荷转移(CT)复合物进行了光谱研究。通过在
CCl4溶液中测定1:1电荷转移复合物的平衡常数和吉布斯能变。研究中包含的羰基衍
生物在 中的ICl碱性尺度与相同溶剂中的I2碱性尺度有很好的相关性。为了阐明这些CT复合物的结构,进行了HF/
LAN
L2DZ*和MP2(full)/
LAN
L2DZ*的从头计算。根据取代基的特征,可以发现两种不同的构象。在其中一种构象中,ICl部分位于羰基平面内,而在另一种构象中,ICl亚单元则垂直于CO基团。对于HOMO具有明显π特征的笨重取代基,垂直复合物更为有利。这两种类型的复合物可以通过光谱方法区分,因为它们在不同波长下呈现CT吸收。在这两种复合物中,羰基与ICl之间的相互作用主要是静电相互作用。通过使用Taft–Topsom模型分析取代基效应。实验证据与理论估计之间呈现良好的线性关系。