INNER-SHELL SPECTROSCOPY OF PARA-BENZOQUINONE, HYDROQUINONE, AND PHENOL - DISTINGUISHING QUINOID AND BENZENOID STRUCTURES
INNER-SHELL SPECTROSCOPY OF PARA-BENZOQUINONE, HYDROQUINONE, AND PHENOL - DISTINGUISHING QUINOID AND BENZENOID STRUCTURES
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DOI：
10.1021/j100195a018
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发表时间：
1992-08-06
影响因子：
--
通讯作者：
HITCHCOCK, AP
中科院分区：
文献类型：
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作者：
FRANCIS, JT;HITCHCOCK, AP
振子强度为C Is和0 ls激发的气相对苯醌，氢醌，苯酚已来自电子能量损失谱记录电偶极子散射条件下。光谱分配已协助扩展休克尔（EHMO）计算内进行的等效核心类比，以及通过比较以前记录的光谱苯，丙烯酸，1，4-环己二酮，丙酮。EHMO结果与实验芯激发光谱的两种方法进行了探讨。从完整的电荷矩阵推导出的结果被认为是优选的。对苯醌的C1 s光谱的几个特征可以与该物种的醌型结构相关联，即第二个pi* 共振比第一个更强，并且Cls（C=C）-> pi*LUMO（b2 g）跃迁的位移比苯型物种中最低的Cls-> pi* 跃迁的位移低1.6 eV。这种转变与芳族稳定性的丧失有关。EHMO计算对苯醌在非平衡几何和相关分子的光谱分配提供了进一步的见解。
Oscillator strengths for C Is and 0 ls excitation of gas-phase p-benzoquinone, hydroquinone, and phenol have been derived from electron energy loss spectra recorded under electric dipole scattering conditions. Spectral assignments have been aided by extended Huckel (EHMO) calculations carried out within the equivalent core analogy, as well as by comparisons to previously recorded spectra of benzene, acrylic acid, 1,4-cyclohexanedione, and acetone. Two methods of relating EHMO results to experimental core excitation spectra are explored. That derived from the complete charge matrix is found to be preferable. Several features of the C 1s spectrum of p-benzoquinone can be associated with the quinoid structure of this species, namely a second pi* resonance more intense than the first, and a shift of the C ls(C=C) --> pi*LUMO(b2g) transition to 1.6 eV below that of the lowest C ls --> pi* transition in benzenoid species. This shift is associated with the loss of aromatic stabilization. EHMO calculations of p-benzoquinone in nonequilibrium geometries and of related molecules provide further insight into spectral assignments.