Hydrogen bonding in substituted formic acid dimers

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Hydrogen bonding is crucial in molecular interactions.
• Formic acid derivatives are fundamental organic compounds.
• Understanding substituent effects on molecular stability is important.

Purpose of the Study:

• To investigate the stability and hydrogen bonding characteristics of formic acid derivatives.
• To determine the most stable dimer among XCOOH (X = H, F, Cl, CH3).
• To analyze the nature of hydrogen bonds using topological and charge transfer methods.

Main Methods:

• Density Functional Theory (B3LYP) and MP2 methods were employed.
• Geometry optimization was performed using the 6-311++G(2d,2p) basis set.
• Dimerization energies were extrapolated to the infinite basis set limit using aug-cc-pVXZ (X = D, T) basis sets.
• Topological analysis was conducted using Bader's Atoms in Molecules (AIM) theory.
• Natural Bond Orbital (NBO) analysis was used to study charge transfer.

Main Results:

• The fluorine-substituted formic acid dimer exhibited the highest stability.
• A strong correlation was observed between electron density, its Laplacian at bond critical points, and hydrogen bond length.
• Most dimers displayed conventional hydrogen bonding.
• Some dimers showed improper blue-shifting hydrogen bonds.

Conclusions:

• Fluorine substitution significantly enhances the stability of formic acid dimers.
• AIM and NBO analyses provide valuable insights into hydrogen bond strength and characteristics.
• The study identified both conventional and unusual (blue-shifting) hydrogen bonding patterns in these systems.