Intramolecular London Dispersion Interactions Do Not Cancel in Solution.

Area of Science:

• Supramolecular Chemistry
• Physical Organic Chemistry
• Computational Chemistry

Background:

• Cyclooctatetraene derivatives serve as molecular machines.
• Solvent effects significantly influence molecular conformations and interactions.
• Understanding noncovalent interactions is crucial for molecular design.

Purpose of the Study:

• To quantify the impact of 16 solvents on the folded-unfolded equilibrium of a di-tert-butyl-substituted cyclooctatetraene.
• To elucidate the nature and strength of intramolecular interactions driving isomer stability.
• To investigate the role of dispersion forces in noncovalent bonding.

Main Methods:

• Temperature-dependent nuclear magnetic resonance (NMR) spectroscopy to measure isomer equilibrium.
• Energy Decomposition Analysis (EDA) using density functional theory (DFT) and ab initio methods.
• Computational modeling to analyze noncovalent interactions.

Main Results:

• The folded 1,6-isomer, with proximate tert-butyl groups, is enthalpically favored over the unfolded 1,4-isomer.
• London dispersion interactions were identified as the predominant force stabilizing the folded isomer.
• Solvent polarity and type did not alter the fundamental energetic preference for the folded state.

Conclusions:

• Di-tert-butyl-substituted cyclooctatetraene acts as a molecular balance sensitive to noncovalent interactions.
• Dispersion forces play a dominant role in the intramolecular stabilization of the folded isomer.
• The observed equilibrium is robust across a range of solvents, highlighting the strength of these specific noncovalent interactions.