Department of Chemistry, Faculty of Science, Fukuoka University, Fukuoka 814-0180, Japan.
J Phys Chem A. 2012 Sep 20;116(37):9271-8. doi: 10.1021/jp306609f. Epub 2012 Sep 11.
The vibrational spectra of the hydrated and methanol-solvated aminopyrazine, 2-aminopyridine and 3-aminopyridine in supersonic jets have been measured in terms of IR-UV double-resonance spectroscopy. Comparing the IR spectrum of aminopyrazine with those of 2-aminopyridine and 3-aminopyridine clusters, we determine the solvation structure of aminopyrazine to be a similar cyclic structure as hydrated 2-aminopyridine clusters [Wu, et al., Phys. Chem. Chem. Phys. 2004, 6, 515]. In the case of monohydrated aminopyrazine cluster, one of the normal modes composed of the hydrogen-bonded OH and NH stretching local modes gives the anomalously weak IR intensity, which is ascribed to the cancellation of the dipole moment change between the OH and NH stretching local modes. The solvated 3-aminopyridine clusters forms the hydrogen-bond between the pyridyl nitrogen atom and the OH group, but the amino group is indirectly affected to induce slight blue shift of the NH(2) stretches. This phenomenon is explained by inductive effect where the electron withdrawing from the amino group upon the solvation results in a "quinoid-like" structure of the amino group.
水合和甲醇溶剂化的氨基吡嗪、2-氨基吡啶和 3-氨基吡啶在超音速射流中的振动光谱已经通过红外-紫外双共振光谱法进行了测量。通过将氨基吡嗪的红外光谱与 2-氨基吡啶和 3-氨基吡啶簇的红外光谱进行比较，我们确定了氨基吡嗪的溶剂化结构为类似于水合 2-氨基吡啶簇的环状结构[Wu 等人，Phys. Chem. Chem. Phys. 2004, 6, 515]。在一水合氨基吡嗪簇的情况下，由氢键 OH 和 NH 伸缩局部模式组成的一个正则模态给出了异常弱的红外强度，这归因于 OH 和 NH 伸缩局部模式之间的偶极矩变化的抵消。溶剂化的 3-氨基吡啶簇形成了吡啶氮原子和 OH 基团之间的氢键，但氨基基团受到间接影响，导致 NH(2)伸缩的轻微蓝移。这种现象可以通过诱导效应来解释，即氨基基团在溶剂化时从氨基基团中吸引电子，导致氨基基团呈现出“醌式样”结构。
