Faculty of Science, University of Kinshasa, B.P. 190 Kinshasa XI, DR Congo.
J Phys Chem A. 2012 Aug 23;116(33):8608-14. doi: 10.1021/jp3038158. Epub 2012 Aug 13.
A density functional theory (DFT) study is performed to determine the stability of the complexes formed between either the N or O site of 3-methyl-4-pyrimidone and 1-methyl-2-pyrimidone molecules and different ligands. The studied ligands are boron and alkali Lewis acids, namely, B(CH(3))(3), HB(CH(3))(2), H(2)B(CH(3)), BH(3), H(2)BF, HBF(2), BF(3), Li(+), Na(+), and K(+). The acids are divided into two groups according to their hardness. The reactivity predictions, according to the molecular electrostatic potential (MEP) map and the natural bond orbital (NBO) analysis, are in agreement with the calculated relative stabilities. Our findings reveal a strong regioselectivity with borane and its derivatives preferring the nitrogen site in both pyrimidone isomers, while a preference for oxygen is observed for the alkali acids in the 3-methyl-4-pyrimidone molecule. The complexation of 1-methyl-2-pyrimidone with these hard alkali acids does not show any discrimination between the two sites due to the presence of a continuous delocalized density region between the nitrogen and the oxygen atoms. The preference of boron Lewis acids toward the N site is due to the stronger B-N bond as compared to the B-O bond. The influence of fluorine or methyl substitution on the boron atom is discussed through natural orbital analysis (NBO) concentrating on the overlap of the boron empty p-orbital with the F lone pairs and methyl hyperconjugation, respectively. The electrophilicity of the boron acids gives a good overall picture of the interaction capabilities with the Lewis base.
采用密度泛函理论（DFT）研究了 3-甲基-4-嘧啶酮和 1-甲基-2-嘧啶酮分子的 N 或 O 位点与不同配体形成的配合物的稳定性。研究的配体是硼和碱路易斯酸，即 B(CH(3))(3)、HB(CH(3))(2)、H(2)B(CH(3))、BH(3)、H(2)BF、HBF(2)、BF(3)、Li(+)、Na(+)和 K(+)。根据硬度将酸分为两组。根据分子静电势（MEP）图和自然键轨道（NBO）分析的反应性预测与计算的相对稳定性一致。我们的研究结果表明，硼烷及其衍生物具有很强的区域选择性，更喜欢两种嘧啶酮异构体中的氮位，而碱路易斯酸则更喜欢 3-甲基-4-嘧啶酮分子中的氧位。这些硬碱路易斯酸与 1-甲基-2-嘧啶酮的络合由于氮原子和氧原子之间存在连续的离域密度区域，因此两个位点之间没有任何选择性。硼路易斯酸对 N 位的偏好归因于 B-N 键比 B-O 键更强。通过自然轨道分析（NBO）讨论了硼原子上氟或甲基取代的影响，重点是硼空 p 轨道与 F 孤对和甲基超共轭的重叠。硼酸的电负性很好地描述了与路易斯碱的相互作用能力。
