Al-Otaibi Jamelah S
Department of Chemistry, College of Science, Princess Nourah bint Abdulrahman University, Riyadh, 11951 Saudi Arabia.
Springerplus. 2015 Oct 9;4:586. doi: 10.1186/s40064-015-1363-2. eCollection 2015.
2-amino pyridine derivatives have attracted considerable interest because they are useful precursors for the synthesis of a variety of heterocyclic compounds possessing a medicinal value. In this work we aim to study both structural and electronic as well as high quality vibrational spectra for 2-amino-3-methylpyridine (2A3MP) and 2-amino-4-methylpyridine (2A4MP).
Møller-Plesset perturbation theory (MP2/6-31G(d) and MP2/6-31++G(d,p) methods were used to investigate the structure and vibrational analysis of (2A3MP) and (2A4MP). Tautomerization of 2A4MP was investigated by Density Functional Theory (DFT/B3LYP) method in the gas phase. For the first time, all tautomers including NH → NH conversions as well as those usually omitted, NH → CH and CH → CH, were considered. The canonical structure (2A4MP1) is the most stable tautomer. It is 13.60 kcal/mole more stable than the next (2A4MP2). Transition state structures of pyramidal N inversion and proton transfer were computed at B3LYP/6-311++G(d,p). Barrier to transition state of hydrogen proton transfer is calculated as 44.81 kcal/mol. Transition state activation energy of pyramidal inversion at amino N is found to be 0.41 kcal/mol using the above method. Bond order and natural atomic charges were also calculated at the same level. The raman and FT-IR spectra of (2A3MP) and (2A4MP) were measured (4000-400 cm(-1)). The optimized molecular geometries, frequencies and vibrational bands intensity were calculated at ab initio (MP2) and DFT(B3LYP) levels of theory with 6-31G(d), 6-31++G(d,p) and 6-311++G(d,p) basis sets. The vibrational frequencies were compared with experimentally measured FT-IR and FT-Raman spectra.
Reconsidering the vibrational analysis of (2A3MP) and (2A4MP) with more accurate FT-IR machine and highly accurate animation programs result in new improved vibrational assignments. Sophisticated quantum mechanics methods enable studying the transition state structure for different chemical systems.
2-氨基吡啶衍生物因其是合成多种具有药用价值的杂环化合物的有用前体而备受关注。在本工作中，我们旨在研究2-氨基-3-甲基吡啶（2A3MP）和2-氨基-4-甲基吡啶（2A4MP）的结构、电子性质以及高质量的振动光谱。
采用Møller-Plesset微扰理论（MP2/6-31G(d)和MP2/6-31++G(d,p)方法）研究了（2A3MP）和（2A4MP）的结构和振动分析。通过密度泛函理论（DFT/B3LYP）方法在气相中研究了2A4MP的互变异构。首次考虑了所有互变异构体，包括NH→NH转化以及通常被忽略的NH→CH和CH→CH转化。标准结构（2A4MP1）是最稳定的互变异构体。它比下一个（2A4MP2）稳定13.60千卡/摩尔。在B3LYP/6-311++G(d,p)水平上计算了锥形N反转和质子转移的过渡态结构。计算得到氢质子转移的过渡态能垒为44.81千卡/摩尔。使用上述方法发现氨基N处锥形反转的过渡态活化能为0.41千卡/摩尔。还在同一水平上计算了键级和自然原子电荷。测量了（2A3MP）和（2A4MP）的拉曼光谱和傅里叶变换红外光谱（4000 - 400厘米⁻¹）。在从头算（MP2）和DFT（B3LYP）理论水平上，使用6-31G(d)、6-31++G(d,p)和6-311++G(d,p)基组计算了优化的分子几何结构、频率和振动带强度。将振动频率与实验测量的傅里叶变换红外光谱和傅里叶变换拉曼光谱进行了比较。
使用更精确的傅里叶变换红外光谱仪和高精度的动画程序重新考虑（2A3MP）和（2A4MP）的振动分析，得到了新的改进的振动归属。复杂的量子力学方法能够研究不同化学体系的过渡态结构。
