Cooperative effect on phenolic νO-H frequencies in 1:1 hydrogen bonded complexes of o-fluorophenols with water: A matrix isolation infrared spectroscopic study (original) (raw)
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The Journal of Physical Chemistry A, 2014
O−H stretching infrared fundamentals (ν OH) of phenol and a series of fluorophenol monomers and their 1:1 complexes with benzene have been measured under a matrix isolation condition (8 K). Spectral analysis reveals that ring fluorine substitutions have little effect on phenolic ν O−H as long as the molecules in the matrix are fully dispersed as monomers. The substitution effects are pronouncedly manifested only when the phenols are complexed with benzene, and the measured shift in phenolic ν OH from the monomer value varies from ∼78 cm −1 in phenol to ∼98 cm −1 in 3,4,5-trifluorophenol. The spectral shifts are found to display a linear correlation with the aqueous phase acid dissociation constants (pK a) of the phenols. The spectral changes predicted by electronic structure calculations at several levels of theory are found to be consistent with the observations. Such correlations are also found to exist with respect to different energetic, geometric, and other electronic structure parameters of the complexes. Atoms in Molecules (AIM) analysis shows a distinct bond critical point due to accumulation of electron density at the hydrogen-bonding site. The variation of electron densities both on the hydrogen bond as well the donor O−H group is in accordance with the experimentally observed ν O−H of the various fluorophenol−benzene complexes. Partitioning of binding energies into components following the Morokuma−Kitaura scheme shows that the π-hydrogen-bonded complexes are stabilized predominantly by dispersion interactions, although electrostatics, polarization, and charge-transfer terms have appreciable contribution to overall binding energies. NBO analysis reveals that hyperconjugative charge-transfers from the filled π-orbitals of the hydrogen bond acceptor (benzene) to the antibonding σ*(O− H) orbital of the donors (phenols) display correlations which are fully consistent with the observed variations of spectral shifts. The analysis also shows that the O−H bond dipole moments of all the phenolic species are nearly the same, implying that local electrostatics has only a little effect at the site of hydrogen bonding.
Journal of Physical Chemistry A, 2001
The o-cyanophenol molecule and its hydrogen-bonded complexes with one and two molecules of water and methanol have been investigated by laser-induced fluorescence excitation, dispersed emission, and IR/UV double-resonance spectroscopy combined with DFT calculations. The sole conformer observed in the jet has a cis geometry due to the stabilizing interaction between the OH and CN substituents. The shifts of the electronic transition and the modification of the OH ground-state frequencies together with the calculated geometry point to a cyclic structure of the complexes. In the 1:1 complexes, the solvent OH binds as a proton acceptor to the phenol OH and as a proton donor to the CN group. The 1:2 complexes involve in a similar way the insertion of the solvent dimer (water) 2 or (methanol) 2 between the OH and CN substituents of the molecule. †
The Journal of Physical Chemistry A, 2003
The molecular structure of para-fluorophenol (p-FPhOH) has been calculated using the MP2 and density functional (B3LYP) methods with the extended 6-311++G(df,pd) basis set. The gas-phase structure of this molecule has not been reported, as yet. For the series of phenols, p-XPhOH (X) H, F, Cl, Br), the calculated geometrical parameters and natural atomic charges are compared and discussed. It is shown that in parafluorophenol, the structural changes of the ring are governed chiefly by the electronegativity of fluorine (inductive effect). However, resonance effects induced by the OH and F substituents in the para position also contribute to the geometrical changes of the aromatic ring. The FT-IR spectra of p-fluorophenol and its ODdeuterated derivative (p-FPhOD) in carbon tetrachloride and cyclohexane solutions were measured, in the frequency range of 3700-400 cm-1 , and the experimental integrated infrared intensities were determined. The harmonic frequencies and IR intensities of p-FPhOH and p-FPhOD were calculated with the B3LYP method using the 6-311++G(df,pd) basis set. The unequivocal assignment of the experimental spectra has been made on the basis of the calculated potential energy distribution, PED. The characteristic "marker" IR bands for phenol and its para-halogeno derivatives are discussed. The unusual quenching of the infrared intensities of several bands in the spectra of p-fluorophenol has been explained.
Hydrogen bonding in 2-fluorophenol, and rotation about the CO bond: A molecular orbital study
1987
Calculations were done at the 6-31G level on 2-fluorophenol for the HOCC dihedral angle @ = 0, 30, 60, 90, 120, 150 and 180", assumingthat the ring and the 0-and F-atoms lie in the same plane, but otherwise with full geometry optimization. The parameters for the hydrogen bridge in the 0" (cis) rotamer, the five-membered hydrogen bonded ring, and the changes in converting the 180' (trans) into the 0" (cis) rotamer are compared with the corresponding data for the six-membered hydrogen bonded ring in salicylaldehyde. The concomitant changes in bond length and angle in the ring and the progressive decrease in ring area in going from phenol, to fluorobenzene, to the 180" rotamer, to the 0" rotamer show that the perturbation of the OH group as it becomes involved in hydrogen bond formation spreads throughout the entire molecule. The hydrogen bond energy, evaluated as the difference between the ET values for the cis and trans rotamers is 4.0 compared to 11.9 kcal mol-' for salicylaldehyde, in keeping with the more stringent geometrical constraints imposed by the five-membered ring. Analysis of ET as a function of o puts the barrier to rotation at 116" with a barrier height of 5.3 kcal mol-I' and gives the following values for the coefficients in the Fourier cosine series, V, = 1390, V, = 1013, V, = 26 and V, =: 69 cm-'. Comparison with data for the variation of the bond lengths, bond angles and atomic charges in phenol as a function of @ shows that while some are associated with the hydrogen bond formation, others are determined primarily by an interaction of the lone-pair electrons on the oxygen with the n-electron system of the ring.
Computational Chemistry
It is experimentally well established that the phenolic systems such as phenol and diphenols undergo strong hydrogen bonding interaction with water molecule. But, the possible mode hydrogen bonding in phenol-water systems may be of different types. Although, the experimental methods are not always well enough to give the proper hydrogen bonding conformations in the phenol-water complexes. The hydrogen bonding ability in phenol-water systems can directly be influenced by changing the interacting sites in the given molecular systems, which could be investigated by theoretical studies. Generally, in phenol-water system, the hydrogen bonding is taking place through −OH group of phenol with water molecule, and this kind of interactions between phenol-water and diphenol-water complexes have been extensively investigated in electronic ground state by Quantum Mechanical MP4 calculations. It is also very important to study the stability of different phenol-water complexes and to find out the proper phenol-water complexes with minimized interaction energy. This study will also be helpful for understanding the effect of hydrogen bonding interaction in a better way on other aromatic systems.
Contributions, Section of Natural, Mathematical and Biotechnical Sciences, 2017
The quality of theoretical prediction of O-H stretching frequency shifts upon π-hydrogen bonding is analyzed for series of ten complexes between monosubstituted phenols and hexamethylbenzene. Computed O-H frequencies from density functional theory computations at B3LYP/6-311++G(2df,2p) were compared with literature spectroscopic data. The results reveal that the applied theoretical method predicts with an excellent accuracy the O-H frequency shifts [Δυ(OH)] upon π-hydrogen bond formation. Comparisons with analogous theoretical and experimental data for benzene complexes with substituted phenols reveal the magnitude of the methyl groups’ hyperconjugative effects on interaction energies and frequency shifts. The induced by phenol substituents variations in bonding energies and Δυ(OH) are ra-tionalized using theoretically evaluated and experimental parameters.
Magnetic Resonance in Chemistry, 2011
The present study shows that a hydrogen bond between the OH group and the fluorine atom is not involved in the 1h J FH spin-spin coupling transmission either for 4-bromo-2-fluorophenol or 2-fluorophenol. In fact, according to a quantum theory of atoms in molecules analysis, no bond critical point is found between O-H and F moieties. The nature of the transmission mechanism of the Fermi contact term of the 1h J FH spin-spin coupling is studied by analyzing canonical molecular orbitals (see J. Phys. Chem. A 2010, 114, 1044), and it is observed that virtual orbitals play only a quite minor role in its transmission. This is typical of a Fermi contact term transmitted mainly through exchange interactions owing to the overlap of proximate electronic clouds; therefore, it is suggested to identify them as nTS J FH coupling where n stands for the number of formal bonds separating the coupling nuclei. In the cases studied in this work is n = 4. Results presented in this work could provide an interesting rationalization for different experimental signs known in the current literature for proximate J FH couplings.
Theoretical and infrared studies on the conformations of monofluorophenols
Journal of Molecular Structure, 2012
Theoretical calculations for the isolated state indicate the presence of two conformers (A and B) for 2-and 3-fluorophenols, while a single form exists for 4-fluorophenol, as it is well known. The conformer with the hydroxyl hydrogen directed toward the fluorine atom (A) in 2-fluorophenol is calculated to be significantly more stable than the second form, while similar behavior is not obtained for the meta isomer. The infrared C-F stretching intensities confirm these findings in cyclohexane solution, where internal hydrogen bonding in 2-fluorophenol is supposed to be a stabilizing effect of A, but the figure changes in acetonitrile solution and neat liquid, where the most polar conformer B is preferred and intermolecular hydrogen bonding seems to take place, as confirmed by the broadening and shifting of the O-H stretching band. In fact, the strong solvent effect in 2-fluorophenol suggests that conformer A is the most stable form in the isolated state and nonpolar solution predominantly due to dipolar repulsion in B.
Journal of computational chemistry, 2012
We have computationally studied para-X-substituted phenols and phenolates (X= NO, NO 2, CHO, COMe, COOH, CONH 2, Cl, F, H, Me, OMe, and OH) and their hydrogen-bonded complexes with B− and HB (B= F and CN), respectively, at B3LYP/6-311++ G** and BLYP-D/QZ4P levels of theory. Our purpose is to explore the structures and stabilities of these complexes. Moreover, to understand the emerging trends, we have analyzed the bonding mechanisms using the natural bond orbital scheme as well as Kohn–Sham ...
Magnetic Resonance in Chemistry, 2012
Flavonoids are useful compounds in medicinal chemistry and exhibit conformational isomerism, which is ruled by intramolecular interactions. One of the main intramolecular forces governing the stability of conformations is the hydrogen bond. Hydrogen bond involving fluorine covalently bonded to carbon has been found to be rare, but it appears in 2 0 -fluoroflavonol, although the FÁÁÁHO hydrogen bond cannot be considered the main effect governing the conformational stability of this compound. Because 19 F is magnetically active and suitable for NMR studies, the 1h J F,H(O) coupling constant can be used as a probe for such an interaction in 2 0 -fluoroflavonol. In fact, the 1h J F,H(O) coupling was computationally analyzed in this work, and the FÁÁÁHO hydrogen bond was found to be its main transmission mechanism, which modulates this coupling in 2 0 -fluoroflavonol, rather than overlap of proximate electronic clouds, such as in 2-fluorophenol.