Thomas T Darrah, Saethre Leif J, Børve Knut J, Gundersen Maria, Kukk Edwin
Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, USA.
J Phys Chem A. 2005 Jun 16;109(23):5085-92. doi: 10.1021/jp051196y.
The high-resolution carbon 1s photoelectron spectrum of trans-1,3-pentadiene has been resolved into contributions from the five inequivalent carbon atoms, and carbon 1s ionization energies have been assigned to each of these atoms. Spectra have also been measured for propene and 1,3-butadiene at better resolution than has previously been available. The ionization energies for the sp2 carbons are found to correlate well with activation energies for electrophilic addition and with proton affinities. Comparing the results for 1,3-pentadiene with those for ethene, propene, and 1,3-butadiene as well as with results of theoretical calculations makes it is possible to assess the effect of the terminal methyl group in 1,3-pentadiene. As in propene, the methyl group contributes electrons to the beta carbon through the pi system. In addition, there is a significant (though smaller) contribution from the methyl group to the terminal (delta) CH2 carbon, also through the pi system. Most of the effect of the methyl group is present in the ground-state molecule. There are only relatively small contributions from the methyl group to the ionization energies from redistribution of charge in the pi system in response to the removal of a core electron. In addition to these specific effects, there is an overall decrease in average ionization energy as the size of the molecule increases as well as effects that are specific to the conjugated systems in 1,3-butadiene and 1,3-pentadiene. The results provide insight into the reactivity and regioselectivity of conjugated dienes.
反式-1,3-戊二烯的高分辨率碳1s光电子能谱已被解析为五个不等价碳原子的贡献，并且已为这些原子中的每一个指定了碳1s电离能。还以比以前更高的分辨率测量了丙烯和1,3-丁二烯的光谱。发现sp2碳的电离能与亲电加成的活化能和质子亲和力有很好的相关性。将1,3-戊二烯的结果与乙烯、丙烯和1,3-丁二烯的结果以及理论计算结果进行比较，可以评估1,3-戊二烯中末端甲基的影响。与丙烯一样，甲基通过π体系向β碳贡献电子。此外，甲基也通过π体系对末端（δ）CH2碳有显著（尽管较小）的贡献。甲基的大部分影响存在于基态分子中。甲基对由于去除一个内层电子而在π体系中电荷重新分布所产生的电离能的贡献相对较小。除了这些特定影响外，随着分子尺寸的增加，平均电离能总体下降，以及1,3-丁二烯和1,3-戊二烯中共轭体系特有的影响。这些结果为共轭二烯的反应性和区域选择性提供了深入了解。
