Theoretical vs. Experimental Ir Frequency Shifts Upon Π- Hydrogen Bonding: Complexes of Substituted Phenols With Hexamethylbenzene

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.