Infrared spectroscopy of hydrogen bond and substituent effects in electron donor molecules

The frequency shift, , of the O—H stretching mode in the IR spectra of the H-complexes of phenol with electron donor molecules BX_i (B is the n- or -donor center and X_i are substituents; a total of eight series), the change in the Gibbs free energy, G, due to H-complexation, and the parameter (a measure of the ability of BX_i molecules to donate an electron pair; two series) are determined by both the electrostatic interaction and charge transfer in the formation of H-complex. The , G, and values depend not only on the inductive and resonance effects, but also the polarizability of substituents characterized by the parameters.     

Charge transfer theory and vibrational properties of the hydrogen bond

An extension of Mulliken's charge transfer theory leads to the following correlations: the change in the transition moment of the X—H stretching vibration with the enhancement of dipole moment, and the displacement of the X—H stretching frequency with the ionization of donors. Experimental data for a number of hydrogen-bonded complexes are in accord with these predictions.     

Bifurcated hydrogen bond in lithium nitrate trihydrate probed by ab initio molecular dynamics

The hydrogen-bond dynamics of lithium nitrate trihydrate has been studied by a combined approach based on ab initio molecular dynamics simulations and wavelet analysis. The simultaneous bifurcated interaction between one hydrogen atom of water molecules and two oxygen atoms of nitrate ions is the pivotal feature of the crystal structure: this bifurcated interaction has deep effects on the O-H stretching region of the vibrational spectrum. The structural, dynamic, spectroscopic, and electronic properties of the bifurcated hydrogen bond have been investigated computationally, elucidating at the molecular level the differences with weak and strong hydrogen bonds present in the crystal. These studies corroborate the very recent IR experiments performed on the lithium nitrate trihydrate crystal, offering new perspectives to interpreting the vibrational spectra. In fact, this approach allows obtaining two-dimensional plots, which summarize the essential features of both the hydrogen-bond network and IR spectra, resulting in a peculiar "signature" of the bifurcated interaction.     

Influence of calcination and lithium promotion on the surface properties of oxide supports

Thermal treatment and the addition of lithium influence the surface area of the oxides SiO₂, Al₂O₃ and MgO. A calcination temperature 1073 K causes a significant decrease of the surface area of SiO₂ and Al₂O₃; the same is not observed in case of MgO. Systems Li/MgO and Li/SiO₂ are characterized by a much smaller specific surface area than pure oxides thermally treated at the same temperature.     

Cooperative intramolecular hydrogen bond and conformations of thiocalix[4]arene molecules

The joint FTIR spectroscopic study and ab initio quantum-chemical calculations (HF/3-21G and PBE/TZ2P methods) showed that thiocalix[4] arene molecules adopt the cone conformation in CCl₄ solutions. The weakening of the cooperative intramolecular H bond in thiocalix[4]arenes compared to the corresponding calix[4]arenes can be due to the larger thiocalixarene macrocycle, bifurcated hydrogen bond in it, and electron density transfer from the bridging S atom to the benzene ring.     

Study of the hydrogen bond and of the proton transfer between two H2S molecules

The potential energy surface for the H₂S dimer is calculated as the sum of the SCF-MO-LCGO energy with a new, modified, basis set and the estimated dispersion energy. Proton affinities for SH^– and H₂S, and, as their difference, the energy of the proton transfer between two H₂S molecules, are also calculated. Despite the limited basis set used, the results are consistent with experimental data.This work was partly supported by the Polish Academy of Sciences within the project PAN-3.     

Acid-base properties of 1-acyl-5-hydroxypyrazolidines in a hydrogen bond

In solutions, 1-acyl-5-hydroxypyrazolidines form only intermolecular hydrogen bonds in which the proton acceptor is the oxygen atom of the hydroxyl group. These compounds are similar to phenols with respect to the acidity in a hydrogen bond.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 936–939, July, 1989.     

Hydrogen bond studies : 79. Correlation curves for properties of hydrogen bonded water molecules based on ab initio calculations

Correlation curves have been derived from previous ab initio MO-LCAO-SCF calculations made on water molecules in hydrates. The OH-stretching frequency shifts have been correlated with: (a) ratios of the intensity of v?v_OH for bonded water to that for free water, (b) shifts in the OH-distances and (c) quadrupole coupling constants for deuterium in D₂O. Shifts in quadrupole coupling constants are also correlated with shifts in OH-distances. Comparisons have been made with experimental data and the agreement is found to be satisfactory.     

Intermolecular proton transport along the hydrogen bond and the dielectric properties of ice crystals

Conclusion We have attempted here to explain some of the dielectric properties of ice crystals by a concept involving the activated transport of a proton along the hydrogen bond. The choice of the almost symmetrical curve with two minima for a proton in the hydrogen bridge and the rejection of tunnel transport of a proton makes it possible to suggest a theory which explains adequately the dependence of the low frequency dielectric constant on temperature and the phenomenon of the dielectric relaxation of ice. The electrical polarization of an ice crystal according to our model is produced by the defect structure of the ice, the ion pairs, which arises when the proton moves between two neutral water molecules.This particular model does not involve orientation or Bjerrum defects in the ice structure and raises a doubt as to the necessity of introducing them into explanations of the dielectric properties of ice.Moscow Physicotechnical Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 11, No. 3, pp. 415–420, May–June, 1970.     

Solid-liquid equilibrium and the hydrogen bond in crystals

The types of hydrogen-bonded associates formed in phenol and aromatic acid crystals are discussed. A hypothesis is advanced that dissolution of a self-associated solid substance in a nonpolar solvent consists in transferring the associates existing in the crystal phase into saturated solution. The mechanism has been confirmed for several aromatic acids and phenols.     

Reactivity of the C-H bond of organic molecules with various structures in hydrogen abstraction by peroxyl radicals

A model of an early transition state with charge transfer is proposed for calculation of the activation parameters of the abstraction of a hydrogen atom by peroxyl radicals from the molecules of organic compounds. It was shown that the compensation effect in this reaction is due to the fact that the change in the preexponential factor is determined by change in the vibrational component of the entropy of activation. L. M. Litvinenko Institute of Physical Chemistry and Coal Chemistry, Academy of Sciences of Ukraine, Donetsk. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 1, pp. 6–11, January–February, 1997.     

A comparative study of lithium,sodium and hydrogen bonds formed by 1:1 interaction of electron donor molecules with lithium,sodium and hydrogen halides

Dissociation energies of 1:1 complexes of hydrogen, lithium and sodium halides with water, methanol and ammonia vary in the order LiX > NaX > HX, the dissociation energy in the case of lithium bonds being of the order of 200 kJ mol^?1 or more. The dissociation energy of sodium bonds lies in the range 80–120 kJ mol^?1. The magnitude of charge transfer, Δq, between the donor and acceptor molecules is also highest in the case of lithium bonds. The dissociation energies and Δq have been related with various properties of the complexes.     

Defining the bond energy of a strong hydrogen bond

Based on a recent definition of hydrogen-bond energy the hydrogen bond in [HCOO…H…F]^? is weaker than that in [F…H…F]^?, although the former still ranks as a very strong hydrogen bond.     

Design, synthesis and protein-targeting properties of thioether-linked hydrogen bond surrogate helices

Appropriately-placed hydrogen bond surrogates have been demonstrated to efficiently nucleate helical conformations. Herein we describe an efficient method for the synthesis of thioether-based hydrogen bond surrogate (teHBS) helices. A teHBS helix is shown to adopt a stable conformation and target its cognate protein receptor with high affinity.