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Intramolecular Hydrogen Bonding in 2-Hydroxybenzoyl Compounds: Infrared Spectra and Quantum Chemical Calculations

1996; American Chemical Society; Volume: 100; Issue: 18 Linguagem: Inglês

10.1021/jp953527k

1541-5740

Heike Lampert, W. Mikenda, Alfred Karpfen,

Photochemistry and Electron Transfer Studies

IR gas-phase and quantum chemical data that characterize the intramolecular hydrogen bonds in a series of 2-hydroxybenzoyl compounds (Ph(OH)(COY): Y = Cl, OH, SH, OCH3, SCH3, H, CH3, Ph, N(CH(CH3)CH2)2CH2, N(CH2CH2)2CH2, N(CH3)2, NHCH3, NH2, NHNH2) are reported and discussed. The sequences of ν(OH) and of ν(CO) frequencies calculated at HF/3-21G, HF/6-31G**, and B3LYP/6-31G** computational levels agree reasonably well with the corresponding experimental sequences. The consistency of the calculated data is demonstrated by exploiting several relations between calculated frequencies, force constants, and bond distances. It is shown that the sequence of hydrogen bond strengths, as defined either by ν(OH) frequency shifts or by R(O−H) bond distances, may qualitatively be interpreted in terms of two quantities, the R(H···O) hydrogen bond distances and the Q(O) oxygen partial charges, which characterize the intrinsic differences between the carbonyl groups.