"Union is strength": how weak hydrogen bonds become stronger

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Supramolecular Chemistry

Background:

• Conventional hydrogen bonds are well-understood, but weak hydrogen bonds exhibit different driving forces, spatial arrangements, and dynamics.
• Weak hydrogen bonds have binding energies comparable to van der Waals interactions, often forming networks for dimer stabilization.
• Molecules in complexes with weak hydrogen bonds retain significant internal freedom.

Purpose of the Study:

• To analyze molecular adducts stabilized by weak hydrogen bonds using rotational spectroscopy.
• To explore diverse weak hydrogen bond interactions, including C-H···O/N, S-H···O/N, O-H/N-H···halogen/π, and C-H···π/halogen.
• To highlight the significance of weak hydrogen bonds in chiral recognition and biomolecular conformational landscapes.

Main Methods:

• Free jet expansion for generating weakly bound molecular complexes.
• High-resolution rotational spectroscopy for characterizing the structure and dynamics of these complexes.
• Analysis of spectroscopic data to determine intermolecular interactions and geometric parameters.

Main Results:

• Characterization of various weak hydrogen bond types, including those between weak donors and weak acceptors.
• Demonstration that weak hydrogen bonds, even in networks, allow considerable internal molecular motion.
• Evidence for the critical role of weak hydrogen bonds in determining molecular conformation and chiral recognition.

Conclusions:

• Weak hydrogen bonds represent a distinct class of intermolecular forces with unique properties compared to conventional hydrogen bonds.
• Rotational spectroscopy is a powerful tool for elucidating the nature of weak hydrogen bonds in molecular complexes.
• Weak hydrogen bonds play a fundamental role in molecular recognition, self-assembly, and the conformational behavior of biomolecules.