Shoba D, Periandy S, Govindarajan M, Gayathri P
Department of Physics, Periyar Maniammai University, Thanjavur, India; Department of Physics, Alpha College of Engineering & Technology, Puducherry, India.
Department of Physics, Tagore Arts College, Puducherry, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2015 Feb 5;136 Pt B:852-63. doi: 10.1016/j.saa.2014.09.104. Epub 2014 Oct 2.
In this present study, an organic compound Isonicotinic acid methyl ester (INAME) was structurally characterized by FTIR, FT-Raman, and NMR and UV spectroscopy. The optimized geometrical parameters and energies of all different and possible conformers of INAME are obtained from Density Functional Theory (DFT) by B3LYP/6-311++G(d,p) method. There are three conformers (SI, SII-1, and SII-2) for this molecule (ground state). The most stable conformer of INAME is SI conformer. The molecular geometry and vibrational frequencies of INAME in the ground state have been calculated by using HF and density functional method (B3LYP) 6-311++G (d,p) basis set. Detailed vibrational spectral analysis has been carried out and assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The computed vibrational frequencies were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. A study on the electronic properties, such as HOMO and LUMO energies were performed by time independent DFT approach. Besides, molecular electrostatic potential (MEP) and thermodynamic properties were performed. The electric dipole moment (μ) and first hyper polarizability (β) values of the investigated molecule were computed using ab initio quantum mechanical calculations. The calculated results show that the INAME molecule may have microscopic nonlinear optical (NLO) behavior with non zero values. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by gauge independent atomic orbital (GIAO) method.
在本研究中，通过傅里叶变换红外光谱（FTIR）、傅里叶变换拉曼光谱、核磁共振（NMR）和紫外光谱对有机化合物异烟酸甲酯（INAME）进行了结构表征。采用密度泛函理论（DFT）中的B3LYP/6 - 311++G(d,p)方法获得了INAME所有不同可能构象体的优化几何参数和能量。该分子（基态）有三种构象体（SI、SII - 1和SII - 2）。INAME最稳定的构象体是SI构象体。使用HF和密度泛函方法（B3LYP）6 - 311++G(d,p)基组计算了INAME基态的分子几何结构和振动频率。进行了详细的振动光谱分析，并根据峰位和相对强度对观察到的基频带进行了归属。将计算得到的振动频率与实验频率进行了比较，两者吻合良好。采用与时间无关的DFT方法对电子性质进行了研究，如最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）能量。此外，还进行了分子静电势（MEP）和热力学性质的研究。使用从头算量子力学计算方法计算了所研究分子的电偶极矩（μ）和第一超极化率（β）值。计算结果表明，INAME分子可能具有非零值的微观非线性光学（NLO）行为。通过规范无关原子轨道（GIAO）方法计算了该分子的氢核磁共振（(1)H NMR）和碳核磁共振（(13)C NMR）化学位移。
