PERFLUORO EFFECT IN PHOTOELECTRON SPECTROSCOPY .2. AROMATIC MOLECULES
PERFLUORO EFFECT IN PHOTOELECTRON SPECTROSCOPY .2. AROMATIC MOLECULES
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DOI：
10.1021/ja00760a008
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发表时间：
1972-01-01
影响因子：
15
通讯作者：
ROBIN, MB
中科院分区：
文献类型：
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作者：
BRUNDLE, CR;KEUBLER, NA;ROBIN, MB
平面芳族化合物及其全氟衍生物的红外电离势几乎相等，而全氟化合物的电离势比全氢化合物的电离势大几个电子伏（全氟效应）。通过对苯、吡啶、均三嗪、环硼氮烷、对苯醌和萘等化合物及其全氟衍生物的高分辨光电子能谱的比较，得出以下结论：（a）在苯中，轨道排序为ir 3，ir 2（lelg，9.421eV），（3e2g，11.49 eV），m（La 2u，12.3eV），而在六氟苯中a和m的顺序颠倒，（B）吡啶的孤对电子和3个分子轨道几乎简并（9.67和9.80 eV），它们的顺序无法推断。这两个MO之后是2（10.5 eV）和12.45 eV处的MO，其是苯的3e 2g MO的组分。在五氟吡啶中，顺序为3，2，. (c)异三嗪的ir 3、ir 2分子轨道显示出轻微的Jahn-Teller分裂（11.71和12.15 eV），随后是氮孤对AO的e ′（10.41 eV）和a2 ′（13.25 eV）组合，均三嗪的ir 1在14.65 eV处。在三聚氟氰中，C_3N_3F_3，_3，ir_2同样分裂0.4eV，ir_3，_3，（d）环硼氮烷的最高分子轨道是ir_3、ir_2，而不是其他工作者所建议的，它们之后是和，如在苯中一样，（e）萘中的前四个电离不在ir_3、ir_2分子轨道之内，在本工作的第一部分中，1已经确定，当平面非芳族分子的氢原子被氟原子取代时，分子的MO稳定2- 3eV，与IR MO相比，IR MO的稳定性低一个数量级。对MO的特定稳定作用，称为“全氟效应”，在非常非平面的体系中没有观察到（但参见六氟丁二烯0，例如含有甲基的那些，因为在这些体系中，不再能够进行区分，并且所有MO通过取代近似相等地稳定。在对非芳香体系的研究中，采用光电子能谱法测定了体系的连续电离势，然后用高斯型轨道（GTO）计算和Koop-mans定理将其归属于分子轨道。一旦确定，在全氢和全氟分子的过渡相关使用重叠和原子布居分析。在本文中，我们希望将全氟效应应用于平面芳香分子中光电子能带的归属，这些分子对于高质量的GTO计算来说太大了。因此，解释将更加直观，并将完全取决于区分红外和MO的全氟效应的有效性。如将看到的，这种方法导致谱带的合理分配，并且以小的方式证明了在这种类型的化合物中全氟效应的有效性。由于在F2C= CF2这样小的全氟分子中15至20 eV之间的区域是无法辨认的，即使使用GTO计算，也没有希望在这里研究的大得多的分子在该区域中进行详细的分配。然而，在He（II）光谱提供超过20 eV的数据，perhydroperfluoro的相关性再次可识别和分配可以作出。
The ir ionization potentials of planar aromatic systems and their perfluoro derivatives are very nearly equal, whereas the ionization potentials in the perfluoro compounds are several electron volts larger thanin the perhydro compound (the perfluoro effect). Comparisons of the high-resolution photoelectron spectra of benzene, pyridine, s-triazine, borazine, p-benzoquinone, and naphthalene with those of their perfluoro derivatives leadto the following conclusions,(a) In benzene, the orbital ordering is ir3, ir2 (lelg, 9.421 eV),(3e2g, 11.49 eV), m (la2u, 12.3 eV), whilein hexafluorobenzene the ordering of a and m is reversed,(b) The lone-pair and 3 MO’s of pyridine are nearly degenerate (9.67 and 9.80 eV), and their order cannot be deduced. These two MO’s are followed by 2 (10.5 eV) and a MO at 12.45 eV which is a component of the 3e2g MO’s of benzene. In pentafluoropyridine, the ordering is 3, 2,,.(c) The ir3, ir2 MO’s of i-triazine show a slight Jahn-Teller split (11.71 and 12.15 eV), and are followed by the e'(10.41 eV) and a2'(13.25 eV) combinations of the nitrogen lone-pair AO’s, ir, of s-triazine comes at 14.65 eV. In cyanuric fluoride, C3N3F3, 3, ir2 are similarly split by 0.4 eV, and the ir¡ ionization precedes those from the lone pairs,(d) The uppermost MO’s of borazine are ir3, ir2 rather than as suggested by other work-ers, and these are followed by and, as in benzene,(e) The first four ionizations in naphthalene are out of ir MO’s, the fifth out of a MO.In the first part of thiswork, 1 it was established that upon substitution of the hydrogen atoms of a planar nonaromatic molecule by fluorine atoms, the MO’s of the molecule are stabilized by 2-3 eV, in contrast to the ir MO’s, which are an order of magnitude less stabilized. The specific stabilizing effect on the MO’s, termed the “perfluoro effect,” was not observed in grossly non-planar systems (but see hexafluorobutadiene 0 such as those containing the methyl group, for in these the-distinction can no longer be made and all MO’s are approximately equally stabilized by the substitution. In the work on nonaromatic systems, the successive ionization potentials were determined using photoelectron spectroscopy and then assignedto MO’s using Gaussian type orbital (GTO) calculations and Koop-mans’ theorem. Once identified, the transitions in the perhydro and perfluoro molecules were correlated using overlap and atomic population analyses. In the present paper, we wish to apply the perfluoro effect to theassignments of photoelectron bands in planar aromatic mole-cules which are too large for high-quality GTO calculations. Consequently, the interpretations will be more intuitive and will depend totally upon the validity of the perfluoro effect indistinguishing ir and MO’s. As will be seen, this approach leads to a reasonable assignment of the bands, and in a small way justifies the validity of the perfluoro effect in thistype of compound. Since the region between 15 and 20 eV in a perfluorinated molecule as small as F2C= CF2 is undecipherable, even with GTO calculations, there is no hope for a detailed assignment in this region for the much larger molecules studied here. However, where the He (II) spectra provide data beyond 20 eV, the perhydroperfluoro correlations are again recognizable and assignments can be made.