Solvation Effect on the NH Stretching Vibrations of Solvated Aminopyrazine, 2‑Aminopyridine, and 3‑Aminopyridine Clusters

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 116; no. 37; pp. 9271 - 9278
• Main Authors: Yamada, Yuji, Ohba, Hiroumi, Noboru, Yusuke, Daicho, Shigeyuki, Nibu, Yoshinori
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 20.09.2012
• Subjects: Cancellation; Clusters; Dipole moment; Solvation; Spectroscopy; Stretching; Vibration; Vibrational spectra
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp306609f

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 NH2 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.