Matrix-isolation study of the phenol–water complex and phenol dimer (original) (raw)
Related papers
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.
Dimers of phenol in argon and neon matrices
Low Temperature Physics, 2001
The IR absorption spectra of phenol molecules in solid rare gas matrices of argon (10–12 K) and neon (4.5–5 K) are investigated at molar ratios of phenol:matrix of 1:1000 to 1:30 in the frequency range 400–4000 cm−1. Bands of dimers and larger complexes of phenol molecules are observed in the absorption spectrum of both matrices as the matrix ratio decreases. The first additional bands to appear in the spectral region of the stretching vibrations of the O–H group as the phenol concentration increases are two bands attributed to dimers with one and two hydrogen bonds. The absorption coefficients are determined for the bands of stretching vibrations of the O–H and C–O groups, O–H planar bending vibrations of monomers, and the stretching vibrations of the hydrogen-bonded O–H groups of the phenol molecules. The features of the formation of H-bonded complexes in low-temperature matrices are discussed. A model is proposed which permits calculation of the number of monomers, dimers, and la...
Aqueous solutions are complex due to hydrogen bonding (HBing). While gas-phase clusters could provide clues on the solution behavior, most neutral clusters were studied at cryogenic temperatures. Recent results of Shimamori and Fujii provide the first IR spectrum of warm phenol-(H 2 O) 2 clusters. To understand the temperature (T) effect, we have revisited the structure and spectroscopy of phenol-(H 2 O) 2 at all T. While older quantum chemistry work concluded that the cyclic isomers are the most stable, the inclusion of dispersion interactions reveals that they are nearly isoenergetic with isomers forming π-HBs with the phenyl ring. Whereas the OH-stretch bands were previously assigned to purely local modes, we show that at low T they involve a concerted component. We have calculated the (static) anharmonic IR spectra for all low-lying isomers, showing that at the MP2 level, one can single out one isomer (udu) as accounting for the low-T spectrum to 3 cm 1 accuracy. Yet no isomer can explain the substantial blueshift of the phenyl-OH band at elevated temperatures. We describe the temperature effect using ab initio molecular dynamics with a density functional and basis-set (B3LYP-D3/aug-cc-pVTZ) that provide a realistic description of OH· · · O vs. OH· · · π HBing. From the dipole moment autocorrelation function, we obtain good description for both low-and high-T spectra. Trajectory visualization suggests that the ring structure remains mostly intact even at high T, with intermittent switching between OH· · · O and OH· · · π HBing and lengthening of all 3 HBs. The phenyl-OH blueshift is thus attributed to strengthening of its OH bond. A model for three beads on a ring suggests that this shift is partly offset by the elimination of coupling to the other OH bonds in the ring, whereas for the two water molecules these two effects nearly cancel. Published by AIP Publishing. https://doi.org/10.1063/1.5006055
High resolution UV spectroscopy of phenol and the hydrogen bonded phenol-water cluster
The Journal of Chemical Physics, 1996
The S 1 ←S 0 0 0 0 transitions of phenol and the hydrogen bonded phenol͑H 2 O͒ 1 cluster have been studied by high resolution fluorescence excitation spectroscopy. All lines in the monomer spectrum are split by 56Ϯ4 MHz due to the internal rotation of the ϪOH group about the a axis. The barrier for this internal motion is determined in the ground and excited states; V 2 Љ ϭ 1215 cm Ϫ1 , and V 2 Јϭ4710 cm Ϫ1 . The rotational constants for the monomer in the ground state are in agreement with those reported in microwave studies. The excited state rotational constants were found to be AЈϭ5313.7 MHz, BЈϭ2620.5 MHz, and CЈϭ1756.08 MHz. The region of the redshifted 0 0 0 transition of phenol͑H 2 O͒ 1 shows two distinct bands which are 0.85 cm Ϫ1 apart. Their splitting arises from a torsional motion which interchanges the two equivalent H atoms in the H 2 O moiety of the cluster. This assignment was confirmed by spin statistical considerations. Both bands could be fit to rigid rotor Hamiltonians. Due to the interaction between the overall rotation of the entire cluster and the internal rotation, both bands have different rotational constants. They show that V 2 Ј Ͻ V 2 Љ , and that the internal rotation axis is nearly parallel to the a-axis of the cluster. If it is assumed that the structure of the rotor part does not change upon electronic excitation, the internal motion becomes simply a rotation of the water molecule around its symmetry axis. Assuming this motion, barriers of 180 and 130 cm Ϫ1 could be estimated for the S 0 and S 1 states, respectively. The analysis of the rotational constants of the cluster yielded an O-O distance of the hydrogen bond of 2.93 Å in the ground state and 2.89 Å in the electronically excited state. In the equilibrium structure of the cluster, the plane containing phenol bisects the plane of the water molecule.
2006
Molecular dynamics ͑MD͒ simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene/ CCl 4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared vibrational echo spectrum as a function of time, which directly displays the formation and dissociation of the complex through the growth of off-diagonal peaks, and the linear absorption spectrum, which displays two hydroxyl stretch peaks, one for the complex and one for the free phenol. The results of the simulations are compared to previously reported experimental data and are found to be in quite reasonable agreement. The electronic structure calculations show that the complex is T shaped. The classical potential used for the phenol-benzene interaction in the MD simulations is in good accord with the highest level of the electronic structure calculations. A variety of other features is extracted from the simulations including the relationship between the structure and the projection of the electric field on the hydroxyl group. The fluctuating electric field is used to determine the hydroxyl stretch frequency-frequency correlation function ͑FFCF͒. The simulations are also used to examine the number distribution of benzene and CCl 4 molecules in the first solvent shell around the phenol. It is found that the distribution is not that of the solvent mole fraction of benzene. There are substantial probabilities of finding a phenol in either a pure benzene environment or a pure CCl 4 environment. A conjecture is made that relates the FFCF to the local number of benzene molecules in phenol's first solvent shell.
Structures and vibrations of phenol · H2O and d-phenol · D2O based on ab initio calculations
Journal of Molecular Structure: THEOCHEM, 1992
Ab initio electronic structure calculations for phenol and the hydrogen-bonded complexes phenol*H,O and d-phenol*D,O were performed at the HartreeFock 4-31G and 6-31G** levels. Both phenol and phenol.H,O were fully structure optimized. Based on the minimumenergy structures so obtained, full normal coordinate analyses were carried out. The resulting harmonic frequencies were scaled and compared to available experimental data. The agreement is satisfactory and allows for an assignment of a majority of the bands observed in the experimental spectra. Comparison with previous calculations on (H,O), reveals a considerable increase in the strength of the hydrogen bond on going from
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.
Ab initio calculations on phenol–water
Chemical Physics Letters, 2001
The structures of the three phenol-water minima are optimized with MP2 and the interaction-optimized DZPi basis set. Single point calculations are carried out using the slightly larger ESPB basis set, which contains a set of (s,p) bond functions at the midpoint of the hydrogen-bond. The binding energies and hydrogen-bond distances are corrected for basis set superposition error. For all minima, our binding energies D e are larger than the previous theoretical estimates. Despite this, our best estimate of the binding energy D 0 for the global minimum, 21.08 kJ/mol, is about 2 kJ/mol smaller than the experimental values (23:45 AE 0:48 and 22:92 AE 0:36 kJ/mol). Ó