Matrix isolation infrared spectroscopic study of 4-Pyridinecarboxaldehyde and of its UV-induced photochemistry

Cluyts L., Sharma A., Kus N., Schoone K., Fausto R.

SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, vol.171, pp.207-212, 2017 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 171
  • Publication Date: 2017
  • Doi Number: 10.1016/j.saa.2016.08.002
  • Journal Name: SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.207-212
  • Keywords: 4-Pyridinecarboxaldehyde, Matrix isolation infrared spectroscopy, Narrowband UV-induced photochemistry, Quantum chemical calculations, ELECTRON-DIFFRACTION, MOLECULAR-STRUCTURE, INTERNAL-ROTATION, BENZOYL FLUORIDE, MP2 ENERGY, BENZALDEHYDE, SPECTRA, PYRIDINE, MICROWAVE, BARRIERS
  • Anadolu University Affiliated: No

Abstract

The structure, infrared spectrum, barrier to internal rotation, and photochemistry of 4-pyridinecarboxaldehyde (4PCA) were studied by low-temperature (10 K) matrix isolation infrared spectroscopy and quantum chemical calculations undertaken at both Moller-Plesset to second order (MP2) and density functional theory (DFT/B3LYP) levels of approximation. The molecule has a planar structure (Cs point group), with MP2/6-311 ++G(d,p) predicted internal rotation barrier of 26.6 kJ mol(-1), which is slightly smaller than that of benzaldehyde (similar to 30 kJ mol(-1)), thus indicating a less important electron charge delocalization from the aromatic ring to the aldehyde moiety in 4PCA than in benzaldehyde. A complete assignment of the infrared spectrum of 4PCA isolated in an argon matrix has been done for the whole 4000-400 cm(-1) spectral range, improving over previously reported data. Both the geometric parameters and vibrational frequencies of the aldehyde group reveal the relevance in this molecule of the electronic charge back-donation effect from the oxygen trans lone electron pair to the aldehyde C-H anti-bonding orbital. Upon in situ UV irradiation of the matrix-isolated compound, prompt decarbonylation was observed, leading to formation of pyridine. (C) 2016 Elsevier B.V. All rights reserved.