Quantifying the Intrinsic Strength of C-H⋯O Intermolecular Interactions

Area of Science:

• * Computational chemistry
• * Molecular interactions
• * Supramolecular chemistry

Background:

• * The C-H⋯O structural motif's role in molecular interactions is complex, acting in both destabilizing and stabilizing capacities.
• * Quantifying the intrinsic strength of C-H⋯O hydrogen bonds is crucial for understanding their contribution to intermolecular environments.
• * Acrylic acid dimers provide a model system for investigating these interactions due to their C2 symmetry.

Purpose of the Study:

• * To quantify the intrinsic strength of the C-H⋯O hydrogen bond in C2-symmetric acrylic acid dimers.
• * To compare the strength of C-H⋯O hydrogen bonds with the more common O-H⋯O hydrogen bonds.
• * To elucidate the nature of C-H⋯O and O-H⋯O hydrogen bonding through computational analysis.

Main Methods:

• * High-level coupled-cluster theory with singles, doubles, and perturbative triples [CCSD(T)] calculations.
• * Extrapolation to the complete basis set (CBS) limit for accurate energy determination.
• * Symmetry-adapted perturbation theory (SAPT) based on density-functional theory (DFT) treatment of monomers.

Main Results:

• * The intrinsic strength of the C-H⋯O hydrogen bond was determined for acrylic acid dimers.
• * Calculations revealed the C-H⋯O interaction strength is approximately 25% of the O-H⋯O hydrogen bond strength.
• * SAPT-DFT/CBS calculations indicated a similar nature between C-H⋯O and O-H⋯O hydrogen bonding.

Conclusions:

• * The C-H⋯O hydrogen bond is significantly weaker than the O-H⋯O hydrogen bond in the studied system.
• * This quantitative assessment provides a benchmark for understanding the contribution of C-H⋯O interactions.
• * The findings contribute to a deeper understanding of non-covalent interactions in molecular systems.