title: Matrix isolation infrared spectroscopic study of 4-Pyridinecarboxaldehyde and of its UV-induced photochemistry.
abstract: The structure, infrared spectrum, barrier to internal rotation, and photochemistry of 4-pyridinecarboxaldehyde (4PCA) were studied by low-temperature (10K) 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 (Cspoint group), with MP2/6-311++G(d,p) predicted internal rotation barrier of 26.6kJmol-1, which is slightly smaller than that of benzaldehyde (~30kJmol-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 4000-400cm-1spectral 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 CH anti-bonding orbital. Upon in situ UV irradiation of the matrix-isolated compound, prompt decarbonylation was observed, leading to formation of pyridine.
authors.affiliation: Department of Chemical Engineering, Catholic University Leuven, Celestijnenlaan 200F, box 2424, B-3001 Heverlee, Belgium; CQC, Department of Chemistry, University of Coimbra, P-3004-535 Coimbra, Portugal.
authors.forename: Liesel
authors.initials: L
authors.lastname: Cluyts
authors.affiliation: CQC, Department of Chemistry, University of Coimbra, P-3004-535 Coimbra, Portugal.
authors.forename: Archna
authors.initials: A
authors.lastname: Sharma
authors.affiliation: CQC, Department of Chemistry, University of Coimbra, P-3004-535 Coimbra, Portugal; Department of Physics, Anadolu University, TR-26470 Eskişehir, Turkey.
authors.forename: Nihal
authors.initials: N
authors.lastname: Kuş
authors.affiliation: Thomas More University, Kleinhoefstraat 4, B-2440 Geel, Belgium.
authors.forename: Kristien
authors.initials: K
authors.lastname: Schoone
authors.affiliation: CQC, Department of Chemistry, University of Coimbra, P-3004-535 Coimbra, Portugal. Electronic address: rfausto@ci.uc.pt.
authors.forename: Rui
authors.initials: R
authors.lastname: Fausto
keywords: 4-Pyridinecarboxaldehyde; Matrix isolation infrared spectroscopy; Narrowband UV-induced photochemistry; Quantum chemical calculations