Cooperative hydrogen bonding in solution: Influence of molecule structure (original) (raw)
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An ab initio study of the C2H2HF, C2H(CH3)HF and C2(CH3)2HF hydrogen-bonded complexes
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2006
MP2/6-31++G** and B3LYP/6-31++G** ab initio molecular orbital calculations have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the C 2 H 2 HF, C 2 H(CH 3) HF and C 2 (CH 3) 2 HF H-bonded complexes. As expected, the more pronounced effects on the structural properties of the isolated molecules due to complexation was verified for the C C and H F bond lengths, which are directly involved in the H-bond formation. These bond distances increased after complexation. BSSE uncorrected B3LYP binding energies are always lower than the corresponding MP2 values. However, the opposite trend has been verified after BSSE correction by the counterpoise method since it is much lower at B3LYP than at MP2 level. The binding energies for these complexes as well as for the HF acid submolecule modes (the HF stretching and vibrational frequency modes) showed an increasing hydrogen-bonding strength with increasing methyl substitution. The splitting in the HF in-plane and out-of-plane bending modes reflects the anisotropy in the hydrogen-bonding interaction with the system of the C C bond. The H F stretching frequency is shifted downward after complexation and it increases with the methyl substitution. The IR intensities of the HF acid submolecule fundamentals are adequately interpreted through the atomic polar tensor of the hydrogen atom using the charge-charge flux-overlap model. The skeletal stretching modes of the Alkyne submolecule are decreased in the complex. The new vibrational modes arising from complexation show several interesting features.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2010
FTIR spectroscopic study of hydrogen bonding of 1,2-dihydroxybenzene (catechol) with proton acceptors has been carried out. The influence of intramolecular and intermolecular hydrogen bonds on the strengths of each other in complexes of 1,2-dihydroxybenzene with various proton acceptors has been analyzed. It was shown that intramolecular hydrogen bond is strengthened when 1,2-dihydroxybenzene interacts with bases (ethers, amines, nitriles, etc.) in inert solvents. The contribution of the cooperativity of intramolecular hydrogen bonds in the frequency of stretching vibrations of O-H groups linearly depends on the proton acceptor ability of the bases. The solvent effect on hydrogen bond cooperativity in 1,2-dihydroxybenzene-base complexes has been studied. The approach to determine the influence of cooperative effects on the formation of intermolecular complexes with 1,2-dihydroxybenzene is proposed. It was shown that the strength of intramolecular hydrogen bonds in the complexes of 1,2dihydroxybenzene with bases due to cooperativity of interactions increases by 30-70%, and the strength of intermolecular hydrogen bond by 7-22%.
Vibrational …, 2009
DFT calculations with B3LYP and PBE1PBE functionals and 6-311++G(d,p) basis set have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the R-CBBNÁ Á ÁH-F H-bonded complexes with R = NH 2 , CH 3 O, CH 3 , OH, SH, H, Cl, F, CF 3 , CN and NO 2. As expected, it has been verified as a red-shift of the H-F stretching frequency (n H-F), in conformity with the elongation of the bond after complexation. On the other hand, the CBBN stretching frequency (n CB BN) is blue-shifted and corresponds to a shortening of the bond. The binding energies (DE c), including BSSE and ZPVE corrections, show a linear correlation with several structural, electronic and vibrational properties. In particular, an important linear dependence between the binding energy and the calculated dipole moment of the free R-CBBN molecule (m RCN) has been found. This result suggests that m RCN can be a useful quantity in order to predict the ability of this fragment to form a hydrogen-bond. The IR intensities of stretching and bending modes of complexed H-F acid fragment are adequately interpreted through the atomic polar tensor of the hydrogen atom in H-F using the modified CCFO model for infrared intensities. The new vibrational modes arising from complexation show several interesting features.
Russian Journal of General Chemistry, 2007
Solvent effect on the stretching vibration frequencies of the O3H and N3H groups in complexes of phenol and diphenylamine with bases in aprotic and proton-donor solvents was studied by IR spectroscopy. Linear correlations of high quality were obtained between the frequencies of hydrogen-bonded O3H and N3H groups in these complexes in aprotic solvents and a new solvent parameter, S VW. The cooperative effect of a proton-donor solvent on the strength of hydrogen bonds in complexes of phenol and diphenylamine with bases was evaluated. It was demonstrated for the first time that the cooperative effect in the examined systems can lead to both strengthening and weakening of hydrogen bonds.
Vibrational Spectroscopy, 2009
DFT calculations with B3LYP and PBE1PBE functionals and 6-311++G(d,p) basis set have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the R-CBBNÁ Á ÁH-F H-bonded complexes with R = NH 2 , CH 3 O, CH 3 , OH, SH, H, Cl, F, CF 3 , CN and NO 2 . As expected, it has been verified as a red-shift of the H-F stretching frequency (n H-F ), in conformity with the elongation of the bond after complexation. On the other hand, the CBBN stretching frequency (n CB BN ) is blue-shifted and corresponds to a shortening of the bond. The binding energies (DE c ), including BSSE and ZPVE corrections, show a linear correlation with several structural, electronic and vibrational properties. In particular, an important linear dependence between the binding energy and the calculated dipole moment of the free R-CBBN molecule (m RCN ) has been found. This result suggests that m RCN can be a useful quantity in order to predict the ability of this fragment to form a hydrogen-bond. The IR intensities of stretching and bending modes of complexed H-F acid fragment are adequately interpreted through the atomic polar tensor of the hydrogen atom in H-F using the modified CCFO model for infrared intensities. The new vibrational modes arising from complexation show several interesting features. ß
Comparison of Cooperativity in CH···O and OH···O Hydrogen Bonds
Journal of Physical Chemistry A, 2004
The ability of one H-bond in a chain to affect others is assessed by comparing the CH‚‚‚O bonds in (H 2 CO) n and (HFCO) n to the OH‚‚‚O bonds in (H 2 O) n . Both sorts of interactions grow stronger, and the intermolecular distances shorter, as the number of monomers in the chain increases. The degree of cooperativity is generally proportional to the strength of the H-bond, although the CH‚‚‚O bonds in (HFCO) n display a disproportionately high degree of cooperativity. The cooperativity of OH‚‚O and CH‚‚‚O bonds is similar also with respect to electron density loss from the bridging hydrogen atom, and the amount of charge transferred from the protonacceptor molecule to the donor. The covalent CH bonds are shortened upon H-bond formation, and the associated stretching frequencies undergo a blue shift, both opposite to what is observed in OH‚‚‚O systems. These properties exhibit little indication of cooperativity for CH, while the OH bond stretches and red shifts of the OH frequencies are enhanced as n increases. NMR chemical shifts of the bridging proton likewise suggest that CH‚‚‚O bonds are much less cooperative than OH‚‚‚O. Cooperativity is reduced in all systems as the dielectric constant of a surrounding solvent is enhanced.
Relative strength of hydrogen bond interaction in alcohol–water complexes
Chemical Physics Letters, 2004
Hydrogen binding energies are calculated for the different isomers of 1:1 complexes of methanol, ethanol and water using ab initio methods from MP2 to CCSD(T). Zero-point energy vibration and counterpoise corrections are considered and electron correlation effects are analyzed. In methanol-water and ethanol-water the most stable heterodimer is the one where the water plays the role of proton donor. In methanol-ethanol the two isomers have essentially the same energy and no favorite heterodimer could be discerned. The interplay between the relative binding energy is briefly discussed in conjunction with the incomplete mixing of alcohol-water systems.
A comprehensive analysis of hydrogen bond interactions based on local vibrational modes
International Journal of Quantum Chemistry, 2012
Local stretching modes for 69 different DH single bonds and 58 H• • • A H-bonds are calculated at the ωB97X-D/aug-cc-pVTZ level of theory to describe the changes in donor D and acceptor A upon forming the hydrogen-bonded complex. The intrinsic strength of the DH and AH interactions is determined utilizing the properties of a well-defined set of local, uncoupled vibrational modes. The local mode stretching force constant k a (HA) provides a unique measure of bond strength for both covalently and electrostatically bonded complexes. Generally applicable bond orders are derived, which can be related to the binding energies of the hydrogen bonded complexes. Although the red shifts in the DH stretching frequencies can be used to detect hydrogen bonding, they are not sufficient to assess the strength of hydrogen bonding. It is demonstrated that the calculated BSSE-corrected binding energies of hydrogen bonded complexes are related to the sum of bond order changes caused by hydrogen bonding.The covalent character of charge assisted hydrogen bonds is explained. Because local mode frequencies can also be derived from experimental normal mode frequencies, a new dimension in the study of hydrogen bonding is gained.