A theoretical investigation of the nature of the π-H interaction in ethene–H2O, benzene–H2O, and benzene–(H2O)2

Abstract

We have carried out a detailed investigation of the nature of the π-H interaction in the ethene–H2O, benzene–H2O, and benzene–(H2O)2 complexes using large basis sets (ranging from 6-31+G* to TZ2P++) and high levels of theory. The minimum geometries, and hence the vibrational frequencies, of all the complexes have been obtained at the second order Mo/ller–Plesset (MP2) level of theory. The binding energy of the ethene–H2O complex is only about 1 kcal/mol lower than that of the benzene–H2O complex. In the benzene–(H2O)2 complex, the interaction of benzene with the π-bonded water to that with the second water is nearly equivalent. In order to explain the above interesting facets of the interaction of water with benzene and ethene, the interaction energies were decomposed into the individual interaction energy components using the recently developed symmetry adapted perturbation theory (SAPT) program. The SAPT results indicate that the repulsive exchange energies play a crucial role in governing the energies and geometric preferences of these complexes. A detailed analysis of the vibrational frequencies of these complexes has also been done to examine the changes in the frequencies of the monomers upon complexation. It is found that changes in the out-of-plane bending frequencies of benzene and ethene can be correlated to the interaction energies of these complexes, in particular the exchange energy.

Ab initio molecular dynamics study of aqueous solvation of ethanol and ethylene

“…The BLYP result shows a significant π-H binding energy of ≈ 1.4 kcal/mol. However, in MP2 [44,46,47] and CCSD [46] calculations, binding energies are ≈ 1-2 kcal/mol stronger, accompanied by a shorter π-H bond with differences of 0.12Å and 0.14Å for EW1a and EW1b, respectively. The comparison with the experimental value gives a similar picture with the BLYP underestimating the binding energy ≈ 2 kcal/mol.…”

“…In the EW1a structure the waterplane is parallel to the C=C bond, whereas in EW1b it is orthogonal. In table III we compare the CPMD-BLYP geometries with ADF-BLYP and MP2 [44,47] and CCSD [46] results. Fig.…”

“…complex ethanol/ethylene water total single-water - [70], d: microwave experiment [69] e: MP2/6-311+G(2df,2p)+BSSE [75], f: MP2/TZ2P++ [44], g: MP2/6-311+G(2d,2p) [47], h: CCSD(T)/aug-cc-pVDZ [46], i: Matrix isolation study [41], j: MP2/aug-cc-pVDZ [45], and k: Matrix isolation study [40]. For (e), (f), (g), and (h) we gave the BSSE-corrected (lowest value) and the non-BSSE corrected values (highest value).…”

“…Several experimental techniques have been applied to measure the strength of this interaction, such as the matrix isolation study of Engdahl and Nelander [40,41], the microwave spectra study of Andrews and Kuczkowski [42] and the molecular-beam measurements of Peterson and Klemperer [43]. Recently Tarakeshwar et al [44,45,46] and Dupré and Yappert [47] have performed calculations on the ethylene-water complexes with high level ab initio methods. The interaction is weak compared to a hydrogen bonds such as in the water dimer.…”

Mutual solubilities of hydrocarbons and water with the CPA EoS

“…For the aromatics compounds a single association site is considered, cross associating with water, as suggested by some theoretical and experimental evidence [37,38].…”