Abstract
The current study belongs to a series of investigations of polycyclic aromatic compounds containing intramolecular hydrogen bonds. Close proximity of the coupled aromatic system and hydrogen bridges gives rise to resonance-assisted hydrogen bonding phenomena. Substituted naphthols are ideally suited for this kind of investigation. The parent compound, 1-hydroxy-8-methoxy-3-methylnaphthalene, and its derivative, 1-bromo-5-hydroxy-4-isopropoxy-7-methylnaphthalene, both with known crystal structure, are investigated. Car-Parrinello molecular dynamics (CPMD) is chosen as a theoretical background for this study. Gas phase and solid state simulations are carried out. The effect of Grimme’s dispersion corrections is also included. The report presents time evolution of structural parameters, spectroscopic signatures based on the CPMD simulations, and comparison with available experimental data. We show that the proton transfer phenomena do not occur within the simulations, which is consistent with evaluation based on the acidity of the donor and acceptor sites. The effects of the substitution in the aromatic system and change of the environment (gas vs. condensed phase) are of similar magnitude.
Highlights
Hydrogen bonds are objects of experimental and theoretical studies due to their importance and diversity [1, 2]
The use of molecular dynamics allows us to observe the effect of introduction of bromine and isopropyl functions on the dynamics of the bridge proton, including its tendency to deviate from the molecular plane
Molecular dynamics schemes are well suited for this kind of investigation, because they allow focusing on the selected degrees of freedom while including the remaining degrees of freedom in a statistically averaged manner
Summary
Hydrogen bonds are objects of experimental and theoretical studies due to their importance and diversity [1, 2]. The objects of this study, compounds 1 and 2, cannot be classified as “proton sponges”, but they exhibit structural similarities to that group related to flexibility of the system and distance modulation between the donor and acceptor atoms. The free rotations of the OH group from one side and methoxy or isopropoxy groups from the other side are restricted because of the stabilizing intramolecular hydrogen bond. Both hydrogen bonds, these present in DMANH+ and in the studied cases, are resonance-assisted, but — as explained in Scheme 1 — the “proton sponge”-like behavior could be assigned to the phenolate anions of 1 and 2, not to the compounds themselves. The study will concentrate rather on the impact of substitution on the molecular properties
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