Weak hydrogen bond topology in 1,1-difluoroethane dimer: A rotational study

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Supramolecular Chemistry

Background:

• Understanding non-covalent interactions is crucial for molecular assembly.
• Weak hydrogen bonds, like C-H⋯F-C, play a significant role in stabilizing molecular complexes.
• 1,1-difluoroethane is a relevant molecule for studying such interactions due to its fluorine atoms.

Purpose of the Study:

• To investigate the structure and stability of the 1,1-difluoroethane dimer.
• To identify and characterize different isomers of the dimer.
• To determine the relative stability and population of these isomers.

Main Methods:

• Pulsed-jet Fourier transform microwave spectroscopy was employed.
• Rotational spectra of the dimer and its 13C isotopologues were measured.
• Relative intensity measurements of spectral transitions were used to estimate isomer populations.

Main Results:

• Two stable isomers of the 1,1-difluoroethane dimer were detected.
• Both isomers are stabilized by three C-H⋯F-C weak hydrogen bonds.
• The most stable isomer has a population ratio of approximately 6:1 compared to the second isomer.
• Structural determination was achieved for the global minimum isomer using isotopologue data.

Conclusions:

• The experimental results indicate a larger energy difference between the two isomers than predicted by ab initio calculations.
• The findings provide valuable insights into the nature and strength of weak hydrogen bonds in molecular dimers.
• This study contributes to the understanding of non-covalent interactions in fluorinated organic molecules.