Department of Physics, Afyon Kocatepe University, 03040 Afyonkarahisar, Turkey.
Spectrochim Acta A Mol Biomol Spectrosc. 2012 Jul;93:33-46. doi: 10.1016/j.saa.2012.02.110. Epub 2012 Mar 7.
Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of 4-chloro-3,5-dinitrobenzoic acid (CDNBA) were carried out by using density functional (DFT/B3LYP) method with 6-311++G(d,p) as basis set. To determine lowest-energy molecular conformation of the title molecule, the selected torsion angle is varied every 10° and molecular energy profile is calculated from 0° to 360°. The optimized geometrical parameters obtained by DFT calculations are in good conformity with single crystal XRD data. The FT-IR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational wavenumbers as well as their intensities were calculated and a good agreement between observed and scaled calculated wavenumbers has been achieved. The electric dipole moment, polarizability and the first hyperpolarizability values of the CDNBA have been calculated at the same level of theory and basis set. The calculation results also show that the CDNBA molecule may has nonlinear optical (NLO) behavior with non-zero values. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital analysis. Ultraviolet-visible (UV) spectrum of the title molecule has also been calculated using CIS and TD-DFT methods. The calculated energy and oscillator strength almost exactly reproduce the experimental data. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. The thermodynamic properties of the studied compound at different temperatures were calculated.
采用密度泛函（DFT/B3LYP）方法，结合 6-311++G（d，p）基组，对 4-氯-3，5-二硝基苯甲酸（CDNBA）的能量、几何结构和振动波数进行了量子化学计算。为了确定标题分子的最低能量分子构象，选择的扭转角每隔 10°变化一次，并从 0°到 360°计算分子能量曲线。通过 DFT 计算得到的优化几何参数与单晶 XRD 数据吻合良好。在凝聚态下测量了 FT-IR 和 FT-Raman 光谱。计算了基本振动波数及其强度，并实现了观察到的和缩放计算的波数之间的良好一致性。在相同的理论和基组水平上计算了 CDNBA 的电偶极矩、极化率和一阶超极化率值。计算结果还表明，CDNBA 分子可能具有非线性光学（NLO）行为，具有非零值。通过自然键轨道分析，分析了超共轭相互作用和电荷离域引起的分子稳定性。还使用 CIS 和 TD-DFT 方法计算了标题分子的紫外-可见（UV）光谱。计算的能量和振子强度几乎完全再现了实验数据。通过规范独立原子轨道（GIAO）方法计算了分子的（1）H 和（13）C 核磁共振（NMR）化学位移，并与实验结果进行了比较。计算了不同温度下研究化合物的热力学性质。
