Theoretical studies of the in-solution isomeric protonation of non-aromatic six-member rings with two nitrogens.
Theoretical studies of the in-solution isomeric protonation of non-aromatic six-member rings with two nitrogens.
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含两个氮的非芳香六元环溶液内异构质子化的理论研究。
DOI：
10.1021/jp202241m
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
Messer,WilliamS
中科院分区：
文献类型：
--
作者：
Nagy,PeterI;Messer,WilliamS
为了探索氢键形成的优选位点，理论计算已经进行了一些六元，nonaromatic环允许交替质子化的环氮。对测试分子的气相质子化研究表明，B3 LYP/aug-cc-pvtz和QCISD（T）CBS计算值在约1 kcal/mol内接近实验值，相对焓和自由能有相当大的提高。在IEF-PCM/B3 LYP/aug-cc-pvtz水平计算的相对自由能预测有利的质子化的叔氮，而不是仲氮在水溶液中，并在二氯甲烷溶剂中的饱和环。在C = C键旁边的氮原子上的质子化由于内能的大幅增加而不受欢迎。考虑到0.1摩尔模型系统的长程静电效应的反电势和埃瓦尔德求和的Monte Carlo模拟预测的ΔG（solv）/MC值通常比IEF-PCM计算的负值小。这些结果使得叔氮上的质子化更加有利。溶质-溶剂对能量分布敏感地依赖于所应用的模型。总之，自由移动的阴离子被认为是最相关的模型，具有系统的整体中性，并且应用最少的限制。
For exploring the preferred site for hydrogen bond formation, theoretical calculations have been performed for a number of six-member, nonaromatic rings allowing for alternative protonation on the ring nitrogens. Gas-phase protonation studies for test molecules indicate that the B3LYP/aug-cc-pvtz and QCISD(T)CBScalculations approach the experimental values within about 1 kcal/mol with considerable improvement for relative enthalpies and free energies. Relative free energies calculated at the IEF-PCM/B3LYP/aug-cc-pvtz level predict favorable protonation on the tertiary rather than on the secondary nitrogen both in aqueous solution and in a dichloromethane solvent for saturated rings. Protonation on a nitrogen atom next to a CC bond is disfavored due to a large increase in internal energy. Monte Carlo simulations considering a counterion and Ewald summation for the long-range electrostatic effects for a 0.1 molar model system predict ΔG(solv)/MC values generally less negative than from the IEF-PCM calculations. These results make the protonation on the tertiary nitrogen even more favored. The solute−solvent pair-energy distribution depends sensitively on the applied model. In conclusion, the freely moving anion has been considered as the most relevant model with overall neutrality for the system and applying the least restrictions.