Matrix-isolation infrared spectra of 2-, 3- and 4-pyridinecarboxaldehyde before and after UV irradiation

✍ Scribed by Keiichi Ohno; Takao Itoh; Chiyumi Yokota; Yukiteru Katsumoto

• Publisher: Elsevier Science
• Year: 2006
• Tongue: English
• Weight: 305 KB
• Volume: 825
• Category: Article
• ISSN: 0022-2860
• DOI: 10.1016/j.molstruc.2006.04.033

✦ Synopsis

Three structural isomers of pyridinecarboxaldehydes (2-, 3-and 4-pyridinecarboxaldehyde) have been investigated in detail with matrix-isolation infrared spectroscopy in the 3000-600 cm À1 region, combined with the UV photo-excitation and density-functional theory (DFT) calculations. Two rotamers (anti and syn) for 2-and 3-pyridinecarboxaldehyde (2-and 3-PCA, respectively) and one rotamer for 4-pyridinecarboxaldehyde (4-PCA) were identified upon photo-excitation. Most of the observed bands of each rotamer have been assigned. Both the infrared data and the results of the DFT calculations agree that the syn rotamer is a less stable isomer for 2-and 3-PCA. Formation of an intramolecular CAHÁ Á ÁN hydrogen bond in the anti rotamer of 2-PCA results in a shortening of the aldehyde CAH bond length. The C@O bond length is shortened in the syn rotamer due to the repulsion between the N and aldehyde O atoms. With 2-PCA, both photoinduced rotational isomerism and photolysis were observed upon UV irradiation.