Limits...
Hydrogen bridges of polycyclic aromatic systems with O-H···O bonds--a gas-phase vs. solid-state Car-Parrinello study.

Panek JJ, Jezierska A - J Mol Model (2015)

Bottom Line: Gas phase and solid state simulations are carried out.The effect of Grimme's dispersion corrections is also included.The effects of the substitution in the aromatic system and change of the environment (gas vs. condensed phase) are of similar magnitude.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383, Wrocław, Poland.

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.

No MeSH data available.


Related in: MedlinePlus

Contributions of the bridge protons to the atomic velocity power spectra. Positions are related to the vibrational features, while the intensities are arbitrary. Results of the CPMD simulations
© Copyright Policy - OpenAccess
Related In: Results  -  Collection


getmorefigures.php?uid=PMC4305098&req=5

Fig3: Contributions of the bridge protons to the atomic velocity power spectra. Positions are related to the vibrational features, while the intensities are arbitrary. Results of the CPMD simulations

Mentions: Figure 3 presents the bridge proton contribution to the power spectra of atomic velocity. The upper part of the figure is devoted to the solid state results. The substituent effect is only minimally reflected in the spectra. For both compounds the IR signatures are basically the same. Two regions with strong intensities are detected: 300–1800 cm−1 and 2800–3600 cm−1. The first, low-wavenumber region records most of the molecular motions, since the classical-nuclei model of CPMD does not allow for ideal separation of the constituent molecular oscillators. Thus, the second, high-wavenumber region, collecting the O-H stretching coordinate, is more relevant for the study. The largest motion intensity is registered at the wavenumbers of 3300 cm−1 for 1 and 3250 cm−1 for 2. In the case of the gas phase simulations, more diverse results are obtained. Similar to the solid state computations, two regions with strong intensities are observed. The first region is located for both compounds at 300–1800 cm−1. The second region is located for the parent compound at 3100–3450 cm−1 whereas for its derivative the region is located at 3000–3500 cm−1. The maxima for the O-H stretching are observed for the parent compound 1 at 3400 cm−1 whereas for the compound 2 at 3300 cm−1. As shown, the O-H stretching for 2 is shifted to lower wavenumbers comparing with those obtained for the parent compounds, which is associated with the presence of substituents. The competition between electron-withdrawing and electron-donating properties of the bromine atom (cf. the substituent constants given at the beginning of this section) located in the para position with respect to the hydrogen bond acceptor leads to a small increase in the proton-accepting (nucleophilic) properties of the acceptor, thus contributing to a small strengthening of the bridge. This strengthening is reflected in a small (ca. 100 cm−1) red shift of the corresponding O-H stretching. Concluding, the combined effect of the crystal field and the presence of intramolecular hydrogen bond was able to shield partially the substituent effects in the solid state. An opposite situation is observed for the gas phase simulations, where the computed vibrational signatures detected the influence of substituents on the molecular structure of the investigated compound, resulting in a red shift of ca. 100 cm−1 when moving from 1 to 2. These results are based on atomic velocity power spectra, therefore the apparent intensities are related to motion amplitudes, not to the observable IR data. However, the spread of the stretching region (close to 500 cm−1 in the gas phase) is significant, indicating that the proton in the bridge is moving in a dynamically changing potential.Fig. 3


Hydrogen bridges of polycyclic aromatic systems with O-H···O bonds--a gas-phase vs. solid-state Car-Parrinello study.

Panek JJ, Jezierska A - J Mol Model (2015)

Contributions of the bridge protons to the atomic velocity power spectra. Positions are related to the vibrational features, while the intensities are arbitrary. Results of the CPMD simulations
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4305098&req=5

Fig3: Contributions of the bridge protons to the atomic velocity power spectra. Positions are related to the vibrational features, while the intensities are arbitrary. Results of the CPMD simulations
Mentions: Figure 3 presents the bridge proton contribution to the power spectra of atomic velocity. The upper part of the figure is devoted to the solid state results. The substituent effect is only minimally reflected in the spectra. For both compounds the IR signatures are basically the same. Two regions with strong intensities are detected: 300–1800 cm−1 and 2800–3600 cm−1. The first, low-wavenumber region records most of the molecular motions, since the classical-nuclei model of CPMD does not allow for ideal separation of the constituent molecular oscillators. Thus, the second, high-wavenumber region, collecting the O-H stretching coordinate, is more relevant for the study. The largest motion intensity is registered at the wavenumbers of 3300 cm−1 for 1 and 3250 cm−1 for 2. In the case of the gas phase simulations, more diverse results are obtained. Similar to the solid state computations, two regions with strong intensities are observed. The first region is located for both compounds at 300–1800 cm−1. The second region is located for the parent compound at 3100–3450 cm−1 whereas for its derivative the region is located at 3000–3500 cm−1. The maxima for the O-H stretching are observed for the parent compound 1 at 3400 cm−1 whereas for the compound 2 at 3300 cm−1. As shown, the O-H stretching for 2 is shifted to lower wavenumbers comparing with those obtained for the parent compounds, which is associated with the presence of substituents. The competition between electron-withdrawing and electron-donating properties of the bromine atom (cf. the substituent constants given at the beginning of this section) located in the para position with respect to the hydrogen bond acceptor leads to a small increase in the proton-accepting (nucleophilic) properties of the acceptor, thus contributing to a small strengthening of the bridge. This strengthening is reflected in a small (ca. 100 cm−1) red shift of the corresponding O-H stretching. Concluding, the combined effect of the crystal field and the presence of intramolecular hydrogen bond was able to shield partially the substituent effects in the solid state. An opposite situation is observed for the gas phase simulations, where the computed vibrational signatures detected the influence of substituents on the molecular structure of the investigated compound, resulting in a red shift of ca. 100 cm−1 when moving from 1 to 2. These results are based on atomic velocity power spectra, therefore the apparent intensities are related to motion amplitudes, not to the observable IR data. However, the spread of the stretching region (close to 500 cm−1 in the gas phase) is significant, indicating that the proton in the bridge is moving in a dynamically changing potential.Fig. 3

Bottom Line: Gas phase and solid state simulations are carried out.The effect of Grimme's dispersion corrections is also included.The effects of the substitution in the aromatic system and change of the environment (gas vs. condensed phase) are of similar magnitude.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383, Wrocław, Poland.

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.

No MeSH data available.


Related in: MedlinePlus