Hydrogen bonding between ethynyl aromates and triethylamine: IR spectroscopic and computational study

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Ethynylpyridines (EPs) and ethynylbenzene (EB) are versatile molecules capable of forming hydrogen-bonded complexes.
• The structure and stability of these complexes are influenced by hydrogen-bonding interactions and the surrounding environment.

Purpose of the Study:

• To characterize hydrogen-bonded complexes formed between 2- and 3-ethynylpyridine (EP) and ethynylbenzene (EB) with triethylamine (TEA).
• To investigate the influence of TEA concentration and conformer symmetry on complex stability and spectral properties in tetrachloroethene solution.

Main Methods:

• Infrared (IR) spectroscopy was used to detect and analyze hydrogen-bonded complexes.
• Quantum chemical calculations (B3LYP-D3) were employed to determine complex structures, stabilities, and predict spectral shifts.
• TEA concentration-dependent spectral analysis was performed to study complex formation.

Main Results:

• Experimental evidence confirmed the formation of CH⋯N hydrogen bonds in EPs and EB complexes with TEA, indicated by red-shifted IR signals.
• Complex stability was found to be higher for linear CH⋯N hydrogen bonds and for complexes involving the C_s symmetrical TEA conformer.
• Observed spectral shifts differed from previous gas-phase studies, and association constants were estimated at approximately 0.1 mol⁻¹dm³ at 26°C.

Conclusions:

• The study elucidates the nature of CH⋯N hydrogen bonding in EPs and EB-TEA complexes, highlighting the importance of molecular geometry and conformer effects.
• Computational and experimental data provide insights into the stability and spectral characteristics of these non-covalent interactions in solution.