Differences in structure, energy, and spectrum between neutral, protonated, and deprotonated phenol dimers: comparison of various density functionals with ab initio theory

Abstract

We have carried out extensive calculations for neutral, cationic protonated, anionic deprotonated phenol dimers. The structures and energetics of this system are determined by the delicate competition between H-bonding, H-π interaction and π-π interaction. Thus, the structures, binding energies and frequencies of the dimers are studied by using a variety of functionals of density functional theory (DFT) and Møller-Plesset second order perturbation theory (MP2) with medium and extended basis sets. The binding energies are compared with those of highly reliable coupled cluster theory with single, double, and perturbative triple excitations (CCSD(T)) at the complete basis set (CBS) limit. The neutral phenol dimer is unique in the sense that its experimental rotational constants have been measured. The geometry of the neutral phenol dimer is governed by the hydrogen bond formed by two hydroxyl groups and the H-π interaction between two aromatic rings, while the structure of the protonated/deprotonated phenol dimers is additionally governed by the electrostatic and induction effects due to the short strong hydrogen bond (SSHB) and the charges populated in the aromatic rings in the ionic systems. Our salient finding is the substantial differences in structure between neutral, protonated, and deprotonated phenol dimers. This is because the neutral dimer involves in both H(π)···O and H(π)···π interactions, the protonated dimer involves in H(π)···π interactions, and the deprotonated dimer involves in a strong H(π)···O interaction. It is important to compare the reliability of diverse computational approaches employed in quantum chemistry on the basis of the calculational results of this system. MP2 calculations using a small cc-pVDZ basis set give reasonable structures, but those using extended basis sets predict wrong π-stacked structures due to the overestimation of the dispersion energies of the π-π interactions. A few new DFT functionals with the empirical dispersion give reliable results consistent with the CCSD(T)/CBS results. The binding energies of the neutral, cationic protonated, and anionic deprotonated phenol dimers are estimated to be more than 28.5, 118.2, and 118.3 kJ mol(-1), respectively. The energy components of the intermolecular interactions for the neutral, protonated and deprotonated dimers are analyzed.

Assessing the pKa‐Dependent Activity of Hydroxyl Hydrogen Bond Donors in the Organocatalyzed Cycloaddition of Carbon Dioxide to Epoxides: Experimental and Theoretical Study

“…Additionally, the tendency of the more acidic HBDs to aggregate in the aprotic epoxide medium should be considered. Whereas the energy barriers relative to the dissociation of H‐bonds between molecules of alcohol or phenol are generally relatively low (5–10 kcal/mol), it has been shown that carboxylic acids form trimers in aprotic solvents with stabilization energies in the range of 25 kcal/mol and ΔG<0 . Such tendency to aggregation might have the effect of lowering the HBDs actual concentration with detrimental effects on activity.…”

“…[5] These observations suggest that, in case of analogous compounds with the same Brønsted acidity (3 and ascorbic acid, 4 and 5), also structural features, such as the availability of additional H-bonding moieties, might have an impact on catalytic activity. Whereas the energy barriers relative to the dissociation of H-bonds between molecules of alcohol [41] or phenol [42] are generally relatively low (5-10 kcal/mol), it has been shown that carboxylic acids form trimers in aprotic solvents with stabilization energies in the range of 25 kcal/mol and DG < 0. As expected, [28f] these more acidic compounds show the lowest energy barriers for ring opening and CO 2 insertion (I, II) among all HBDs in Table 2.…”

Solvent Effect on Assembling and Interactions in Solutions of Phenol: Infrared Spectroscopic and Density Functional Theory Study

“…Numerous studies reveal that the OHÁÁÁp interaction is an important factor affecting the assembling process of phenol and its derivatives in aromatic solvents. 8,[11][12][13][14][15][16][17][18][19][20] The strength of the OHÁÁÁp interactions depends on the number, position, and character of the substituents in the aromatic ring of the solute and solvent. IR studies by Saggu et al have shown that the electron withdrawing substituents weaken the OH(D)ÁÁÁp phenol-solvent interactions, while the electron donating groups have an opposite effect.…”

A Spectroscopic and Computational Study of Propofol Dimers and Their Hydrated Clusters

“…Ab initio estimation of the dissociation energies for these systems is by no means an easy task. For example, Kolaski et al performed an outstanding survey on the ability of different combinations of theories and basis sets to determine the dissociation energy of the phenol dimer and its structure 46. As stated in this work, phenol is an exceptional study case.…”