Theoretical Study of the Ionization of Phenol−Water and Phenol−Ammonia Hydrogen-Bonded Complexes

Abstract

The ionization of phenol−water and phenol−ammonia complexes have been determined both using ab initio methods that include electron correlation and the hybrid three-parameter B3LYP density functional method. The most stable structure of phenol−water cation corresponds to the C6H5OH+−H2O non-proton-transferred complex. However, for the phenol−ammonia cation the calculations indicate that the only minimum on the potential energy surface corresponds to the C6H5O−NH4 + proton transferred form. The computed B3LYP adiabatic ionization potentials for C6H5OH−H2O and C6H5OH−NH3 have been determined to be 7.65 and 7.33 eV, respectively. The results obtained indicate that, for the neutral H-bonded systems, the B3LYP density functional method yields very similar results to those obtained with the ab initio MP2 or MCPF methods. However, for the ionized radical cations, B3LYP results compare much better with experiment and to the MCPF method than UMP2. The unscaled B3LYP vibrational frequencies are in very good agreement with the known experimental data.

General and Theoretical Aspects of Phenols

“…Its binding energy of 30.8 kJ mol −1 calculated at the HF/A level rises to 39.9 kJ mol −1 when the MP2(sp)/A calculation is carried out (see Table 36). Note that the latter value agrees with the binding energy of 38.9 kJ mol −1 obtained at the MP2 level in conjunction with the D95 * Dunning basis set 473 . Due to the donor function of the phenolic O−H group in PhOH-w 1 -1, its bond length is slightly elongated by 0.006Å compared to that in bare phenol.…”

“…Surveying briefly the achievements in this area, we would like to mention that the hydrogen-bonded complexes of phenol with proton-accepting molecules such as ethers and alcohols are known to shift the spectra to longer wavelengths from that of the parent phenol by 200-400 cm −1 , depending on the proton-accepting strength of the bases 33, 553, 574, 592 -596 . Clusters of phenols with ammonia 473,577,597 and amines have been studied 25, 164, 473, 550, 568, 577, 588, 598 -607 . Among these studies, it is worth mentioning a recent work 608 using BLYP/6-31G(d,p) calculations on complexes of ammonia with phenol, and its p-nitro, pentafluoro-, 2,6-difluoro-, 4-nitro-and 2-fluoro-4,6-dinitro derivatives.…”

“…Density functional B3LYP calculation of PhOH(H 2 O) n was recently carried out by different groups 473,727 . The ground-state PhOH(H 2 O) 2 complex was first optimized in 1994-1995 696,710 (see also .…”

Theoretical investigation of the hydrogen bonding interaction between substituted phenols and simple O- and N-bases

“…The large size of the phenols has so far restricted the theoretical calculations in small hydrogen-bond acceptor molecules such as H 2 O and NH 3 [34][35][36] or CH 3 OH [37,38]. Most of these studies have been conducted on unsubstituted phenol.…”

Phenol O–H bond dissociation energy in water clusters

“…Phenol-water clusters can be viewed as a simple model, which despite its small size incorporates some relevant aspects of hydrogen bonding in phenol-water solutions. These clusters are model systems for the study of proton transfer in water and have been the subject of several ab initio studies [1 -4], which also analyzed the dependence of the proton transfer on the number of water molecules in the cluster [3,4].…”