FT-IR (7500−1800 cm^-1) Study of Hydrogen-Bond Complexes between Phenols−OH(OD) and Pyridine. Evidence of Proton Transfer in the Second Vibrational Excited State

Abstract

The FT-IR spectra (7500-1800 cm -1 ) of phenol-OH(OD)‚pyridine complexes are investigated at 25 °C in carbon tetrachloride. The pK a of the phenols range from 10.2 to 6, and no proton transfer occurs in the fundamental and first excited vibrational state. The anharmonicities of the ν(OH‚‚‚N) and ν(OD‚‚‚N) vibrations are determined from the experimental frequencies of the fundamental transitions and of the first overtones. The anharmonicities of the ν(OH‚‚‚N) vibration are rather high (between 180 and 235 cm -1 ) and are lower for the ν(OD‚‚‚N) vibration (between 115 and 125 cm -1 ). The first overtone of the ν(OH‚‚‚N) vibration shows for the stronger phenol-OH‚pyridine complexes a splitting assigned to proton transfer in the second vibrational excited state. The principal values of the potential shape (barrier height and values of the two minima) are calculated by the Lippincott-Schroeder potential function. The computed parameters indicate that for the weakest complexes the second minimum potential is higher than the V ) 2 vibrational level, in contrast with the strongest complexes, where the second minimum occurs at lower values than the V ) 2 level. The isotopic ratio varies between 1.346 and 1.255. The lowest values are observed for the complexes where the barrier top is in the vicinity of the first excited vibrational level. The correlation between the enthalpies of complex formation and the experimental and harmonic frequency shifts is discussed. The overtones and combination bands of pyridine are more perturbed in the stronger complexes.

Benquerencia (La Serena - Spain) rock art: An integrated spectroscopy analysis with FTIR and Raman

“…6b-4) and an organic substance (bands 2350, 2454, and 2651 cm −1 ), recorded by micro-ATR-FTIR. Organic ingredient could be attributed to pyridine (Rospenk and Zeegers-Huyskens, 1997); this component is present in some herbs roots and some marshmallows but is also present in different organic compounds.…”

Mid- and Near-Infrared Study of Hydroxyl Groups at a Silica Surface: H-Bond Effect

“…IR spectroscopy has long been used for studying H-bonded systems. − Numerous experimental studies of hydrogen bonds have thus been reported for alcohols and water under various conditions (liquid − and supercritical phases, − rare gas matrices − and gas phases − ). Anharmonicity is a fundamental parameter for understanding the nature of hydrogen bonding since its value is intimately related to the shape of the potential function. ,, Anharmonicity can be calculated by ab initio methods for simple H-bonded systems such as dimers. − For more complicated systems, solutions, or solids, anharmonicity can be derived experimentally by recording overtone spectra in the near-infrared (NIR) − ,− or estimated by deuteration experiments. , Still, the NIR spectral range is seldom examined, and, in the last two decades, only a few NIR studies have examined hydrogen-bonded systems and investigated the effect of hydrogen bonding on anharmonicity. The reasons for this relatively modest research effort are (i) overtones of hydrogen-bonded species have a weak intensity and (ii) the NIR spectra of polyatomic molecules contain numerous bands originating not only from overtones, but also from combinations and/or simultaneous transitions, which makes a precise band assignment often difficult.…”

Enhanced Hydrogen Bonding for the Adsorptive Recovery and Separations of Oxygenated Aromatic Compounds from Renewable Resources

“…Specifically, we study solute adsorption from hexane because this solvent is commonly used for the extraction of compounds from renewable resources (e.g., for producing vegetable oils and spice extracts). Proton transfer is considerably less favorable in low-dielectric environments, − and we anticipate that hydrogen bonding will be an important mechanism for the binding of weakly acidic solutes onto the basic site of the sorbent. − The goal of this study was to determine whether sorbents with more basic binding sites have enhanced abilities to adsorb solutes through a hydrogen-bonding mechanism.

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