Calorimetric and molecular orbital studies of hydrogen bonding between hydrogen fluoride and cyclic ethers

Abstract

The enthalpies of formation of hydrogen bonding complexes AH°were obtained by precision calorimetry for hydrogen fluoride (HF)-furan, HF-tetrahydrofuran (THF), HF-2,5-dimethylfuran (2,5-di-MeF), and HF-2,5-dimethyltetrahydrofuran (2,5-di-MeTHF). The frequency shift Afhf of H-F stretching vibration due to hydrogen bond formation and the equilibrium constant of complex formation were also obtained by infrared spectral measurement and were used to evaluate free energy and entropy of complex formation. The Badger-Bauer relation was found to exist between AH°and Afhf• The AH0 difference between HF-furan (4.8 kcal mol-1) and HF-2,5-di-MeF (6.74 kcal mol-1) was fairly large, while that between HF-THF (7.36 kcal mol-1) and HF-2,5-di-MeTHF (7.41 kcal mol-1) was almost negligible. Ab initio MO calculations were carried out for HF-furan and HF-THF complexes. The calculated equilibrium geometry and hydrogen bonding energy were in good agreement with the trend of experiments. Component analyses showed that the main difference between the two complexes was in the electrostatic interaction and that the presence of conjugated electrons changed only the polarization interaction, resulting in a dipole enhancement.

Very strong hydrogen bonding

“…Even H3P04 can form a strong hydrogen bond to urea107 and this particular 14 and although the expected asymmetry of the hydrogen bond is indicated there has been little interest shown in these ions, apart from the mixed fluoridehalides whose n.m.r. and i.r.…”

Microwave structure determination for the furan-hydrogen chloride complex

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H-3, at 4.64 (br dd, J = 3.0, 1.5 Hz),15 as the equatorial orientation, indicating the right stereochemistry for maytansinol (2).Similarly, treatment of the epoxy aldehyde 20 with lithium enolate of EtOAc (5 equiv in THF, -78 °C, 30 min) now produced the adduct as almost all single isomer 27a (Scheme IV). Its hydroxy group was protected with Me2-Z-BuSiCI [5 equiv and imidazole (12 equiv) in DMF, 35 °C, 12 h], and then the carboxylic ester 27b was hydrolyzed with a mixture of 3 N 1:5:2 KOH-EtOH-THF (45 °C, 7 h) to 27c (52% overall yield from 20).

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A Study on Gamma‐Aminobutyric Acid (GABA) and Its Analogues by Using Molecular Orbital Methods: On Epileptogenicity of New Quinolones

“…However, it is considered that the major interaction in the aqueous solution between the molecules and receptors is the hydrogen bond and that the major factor of hydrogen bond is the electrostatic force. 16 Therefore, the hydrogen bonding will considerably depend on the structure of electrostatic potential and then these results may reflect the state of the interaction in aqueous solution between the molecules.…”