Hydrogen and Halogen Bond Interactions with 2,6-Dimethoxypyridine.

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Noncovalent interactions, including hydrogen and halogen bonding, influence molecular properties.
• Modifying nitrogen-containing heterocycles with electron-donating or withdrawing groups can tune these interactions.
• 2,6-dimethoxypyridine (DMOP) serves as a model to study electron withdrawal effects.

Purpose of the Study:

• To investigate the impact of noncovalent interactions on DMOP using Raman spectroscopy and computational chemistry.
• To explore how electron-withdrawing methoxy groups affect hydrogen and halogen bonding in DMOP.
• To compare charge transfer and spectroscopic changes in hydrogen versus halogen bonding.

Main Methods:

• Raman spectroscopy was employed to analyze experimental spectroscopic changes.
• Computational chemistry, including Natural Bond Orbital (NBO) calculations, was used for theoretical analysis.
• Mixtures of DMOP with water and heptafluoro-2-iodopropane (HFIP) were studied.

Main Results:

• Hydrogen bonding between DMOP and water did not yield discernible spectroscopic changes.
• Computational results indicated preferential water binding to itself or methoxy oxygen atoms.
• Halogen bonding with HFIP resulted in experimental vibrational red shifts in HFIP modes.
• NBO calculations showed greater charge transfer in halogen bonding compared to hydrogen bonding.

Conclusions:

• Competitive binding sites and steric effects in DMOP can hinder nitrogen lone pair accessibility for hydrogen bonding.
• Halogen bonding involving iodine is a robust interaction in solution, even with competing sites.
• This resilient halogen bonding motif holds potential for applications in molecular self-assembly.