1JCH correlates with alcohol hydrogen bond strength

Area of Science:

• Spectroscopy and Quantum Chemistry
• Organic Chemistry
• Supramolecular Chemistry

Background:

• Hydrogen bonding is crucial in molecular interactions.
• Alcohols act as hydrogen bond donors.
• Quantifying hydrogen bond strength is essential for understanding chemical processes.

Purpose of the Study:

• To investigate the relationship between hydrogen bond strength and spectroscopic parameters in alcohol complexes.
• To explore the utility of 1JCH coupling constants as a probe for hydrogen bond dynamics.
• To elucidate the electronic effects governing hydrogen bond interactions in hexafluoroisopropanol complexes.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy, specifically measuring one-bond 13C-1H spin-spin coupling constants (1JCH).
• Synthesis and characterization of various hexafluoroisopropanol (HFIP)-amine complexes.
• Computational analysis of electronic structures and orbital overlaps.

Main Results:

• A strong negative correlation was observed between 1JCH and hydrogen bond enthalpy in HFIP-amine complexes.
• The slope of this correlation was determined to be approximately -0.2 Hz/(kJ mol(-1)).
• A decrease in 1JCH was linked to increased orbital overlap between the hydrogen bonding sigma orbital and vicinal C-H antibonding sigma orbitals.

Conclusions:

• 1JCH is a sensitive NMR parameter reflecting hydrogen bond strength in alcohols.
• The observed correlation provides a quantitative measure for hydrogen bond interactions.
• Electronic effects, specifically orbital overlap, are key determinants of the observed spectroscopic changes.