Costa Alexandre, Costa Elizama Ramos, Silva Adilson Luís Pereira, Tanaka Auro Atsushi, de Jesus Gomes Jaldyr
Universidade Federal de São Carlos, São Carlos, SP, CEP 13565-905, Brazil.
Universidade Estadual do Maranhão, CP 09, São Luís, MA, 65080-040, Brazil.
J Mol Model. 2018 Jan 8;24(1):34. doi: 10.1007/s00894-017-3555-x.
This paper presents a theoretical study of the effects of substituents (F, Cl, Br, CH, and CN) on the aromaticity of borazine (BNH), using density functional theory (DFT) and the Hartree-Fock (HF) method. The calculations to optimize the geometries, structural properties, and vibrational frequencies were performed using the same 6-311G(d,p) and 6-311++G(d,p) basis sets, comparing the methods with experimental results. In the analysis of the NICS values, it was found that that replacing the hydrogen atoms by halogen atoms (F, Cl, and Br) and CH reduced the aromaticity of the borazine molecule, while use of the CN group resulted in NICS values (0.9-2.0 Å) very close to those of borazine, presenting the following order of increasing aromaticity: BNH-(Br) < BNH-(Cl) < BNH-(F) < BNH-(CH) < BNH ~ BNH-(CN). All the spectra of the compounds showed only the presence of transition peaks distant from the UV region, reflecting the large energy difference between the HOMO and LUMO orbitals. After the substitution of the borazine ring, all the compounds presented an intensification of the spectrum, with a shift of the maximum absorbance toward red, indicative of a bathochromic effect. There was a direct inverse relation between the energy gap and the maximum wavelength of the compounds.
本文采用密度泛函理论（DFT）和哈特里 - 福克（HF）方法，对取代基（F、Cl、Br、CH 和 CN）对硼嗪（BNH）芳香性的影响进行了理论研究。使用相同的 6 - 311G(d,p) 和 6 - 311++G(d,p) 基组进行了优化几何结构、结构性质和振动频率的计算，并将这些方法与实验结果进行了比较。在对核独立化学位移（NICS）值的分析中发现，用卤原子（F、Cl 和 Br）和 CH 取代氢原子会降低硼嗪分子的芳香性，而使用 CN 基团会使 NICS 值（0.9 - 2.0 Å）与硼嗪的值非常接近，呈现出以下芳香性递增顺序：BNH-(Br) ＜ BNH-(Cl) ＜ BNH-(F) ＜ BNH-(CH) ＜ BNH ~ BNH-(CN)。所有化合物的光谱仅显示出远离紫外区域的跃迁峰的存在，这反映了最高已占分子轨道（HOMO）和最低未占分子轨道（LUMO）之间的大能量差。在硼嗪环被取代后，所有化合物的光谱都出现了增强，最大吸收峰向红色移动，这表明存在红移效应。化合物的能隙与最大波长之间存在直接的反比关系。
