Kitamura Teruyoshi, Mochida Naomi, Okita Masahiro, Motohashi Mistuya, Ishikawa Hironori, Fujimoto Akira
Department of Environmental Materials Science, Tokyo Denki University, Kanda, Tokyo, Japan.
Spectrochim Acta A Mol Biomol Spectrosc. 2007 Nov;68(3):979-91. doi: 10.1016/j.saa.2007.01.011. Epub 2007 Jan 19.
The hydrogen bonding and amino-imino tautomerization of the systems of 2-amino-3-methoxypyridine (2A3MOP), 2-amino-6-methoxypyridine (2A6MOP), 2-amino-6-n-propoxypyridine (2A6NPOP), 2-amino-6-iso-propoxypyridine(2A6IPOP), 2-amino-4-methoxypyrimidine (2A4MOPM), 4-amino-2-methoxypyrimidine (4A2OPM), 4-amino-6-methoxypyrimidine (4A6MOPM), 2-amino-4-methoxy-6-methylpyrimidine (MMPM), and 2-amino-4,6-dimethoxypyrimidine (DMOPM), with acetic acid (AcOH) in n-hexane at room temperature were investigated by means of the UV absorption and fluorescence spectroscopy. From the UV absorption spectra the presence of the dual hydrogen-bonded complexes that linked by a 1:1 molar ratio with AcOH were found, since the enthalpy changes accompanying the hydrogen bond formation between 2A3MOP, 2A4MOPM, 4A2MOPM, 4A6MOPM, or MMPM, and AcOH were ca. 42.8-61.1kJmol(-1) in n-hexane. The fluorescence spectra of the 2A3MOP/AcOH, 2A4MOPM/AcOH, 4A6MOPM/AcOH, and MMPM/ AcOH systems revealed that the imino-tautomers were produced through double proton transfer in the amino hydrogen-bonded 1:1 complexes in the S1 state, but the imino-tautomer formation for the 4A2MOPM/AcOH system was not found on account of the steric hindrance due to the inversion of the methoxy group in the S1 state. The imino-tautomer for the MMPM/AcOH system fluoresces most intensely among these systems investigated. On the other hand, not only the formation of the corresponding amino dual hydrogen-bonded complex and but also that of imino-tautomer were prevented for the 2A6MOP/AcOH, 2A6NPOPM/AcOH, 2A6IPOP/AcOH, and DMOPM/AcOH systems, because of the steric hindrance of the methoxy group in both the S0 and S1 states. The theoretical approaches by an ab initio molecular orbital calculation were in accord with the experimental results.
通过紫外吸收光谱和荧光光谱研究了2-氨基-3-甲氧基吡啶（2A3MOP）、2-氨基-6-甲氧基吡啶（2A6MOP）、2-氨基-6-正丙氧基吡啶（2A6NPOP）、2-氨基-6-异丙氧基吡啶（2A6IPOP）、2-氨基-4-甲氧基嘧啶（2A4MOPM）、4-氨基-2-甲氧基嘧啶（4A2OPM）、4-氨基-6-甲氧基嘧啶（4A6MOPM）、2-氨基-4-甲氧基-6-甲基嘧啶（MMPM）和2-氨基-4,6-二甲氧基嘧啶（DMOPM）与乙酸（AcOH）在正己烷中于室温下形成的体系中的氢键和氨基-亚氨基互变异构。从紫外吸收光谱中发现存在以1:1摩尔比与AcOH相连的双氢键复合物，因为2A3MOP、2A4MOPM、4A2MOPM、4A6MOPM或MMPM与AcOH之间形成氢键时伴随的焓变在正己烷中约为42.8 - 61.1kJmol⁻¹。2A3MOP/AcOH、2A4MOPM/AcOH、4A6MOPM/AcOH和MMPM/AcOH体系的荧光光谱表明，亚氨基互变异构体是通过S1态氨基氢键连接的1:1复合物中的双质子转移产生的，但由于S1态甲氧基的反转导致空间位阻，未发现4A2MOPM/AcOH体系中有亚氨基互变异构体形成。在这些研究的体系中，MMPM/AcOH体系的亚氨基互变异构体荧光最强。另一方面，对于2A6MOP/AcOH、2A6NPOPM/AcOH、2A6IPOP/AcOH和DMOPM/AcOH体系，由于S0和S1态中甲氧基的空间位阻，不仅阻止了相应氨基双氢键复合物的形成，也阻止了亚氨基互变异构体的形成。从头算分子轨道计算的理论方法与实验结果一致。
