Basicity of organic bases and superbases in acetonitrile by the polarized continuum model and DFT calculations
Basicity of organic bases and superbases in acetonitrile by the polarized continuum model and DFT calculations
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DOI：
10.1039/b814812k
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发表时间：
2009-01-01
影响因子：
3.3
通讯作者：
Maksic, Zvonimir B.
中科院分区：
文献类型：
--
作者：
Glasovac, Zoran;Eckert-Maksic, Mirjana;Maksic, Zvonimir B.
用等密度极化连续体模型研究了大量有机碱和超碱的碱性，包括磷腈、胺、胺、苯胺和吡啶在不同化学环境中的氮碱中心，采用了两种不同的DFT计算方案进行最终单点计算。结果表明，B3LYP/6-311+G(d，p)//B3LYP/6-31G(D)方法对气相和乙腈溶液中碱性氮原子的成键情况有很好的一致性。尝试将实验值pK(A)(MeCN)与MeCN中的质子亲和能(PA)进行了关联。其结果不如使用乙腈中的碱度所获得的结果准确。特别是，PA(MeCN)S经常不能在具有通过电晕效应形成的多个分子内氢(IMH)键的体系中再现pK(A)(MeCN)值。在这种情况下，使用基数是强制性的。对具有多个IMH键的体系进行这些计算的一个有用的推论是，比较理论和实验的pK(A)值可以深入了解溶液中最稳定的构象的结构。
The basicities of a large number of organic bases and superbases, including nitrogen basic centers in various chemical environments occurring in phosphazenes, amidines, amines, anilines and pyridines, have been studied in acetonitrile by the isodensity polarized continuum model employing two DFT computational schemes differing in the basis sets for final single-point calculations. It turned out that the B3LYP/6-311+ G(d,p)//B3LYP/6-31G(d) method serves the purpose giving good agreement for basicities with experiment for both gas phase and acetonitrile solutions treating widely different bonding situations of basic nitrogen atoms on an equal footing. An attempt is made to correlate the experimental pK(a)(MeCN) values with the proton affinities (PA) in MeCN. The results are less accurate than those achieved by using basicities in acetonitrile. In particular, the PA(MeCN)s frequently failed in reproducing the pK(a)(MeCN) values in systems possessing multiple intramolecular hydrogen (IMH) bonds formed via corona effects. In such cases the use of basicities is mandatory instead. A useful corollary of these calculations on systems with multiple IMH bonds is that comparison of the theoretical and experimental pK(a) values can provide an insight into the structure of the most stable conformations in solutions.