Conformational stabilities and structural parameters of (CH3)(n)CH(3-n) CFO molecules

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Conformational analysis of acyl fluorides is crucial for understanding molecular behavior.
• Previous studies have utilized various spectroscopic techniques to investigate molecular structures.

Purpose of the Study:

• To investigate the conformational preferences of propionyl fluoride and 2-methylpropionyl fluoride using variable temperature infrared spectroscopy.
• To determine the enthalpy differences between conformers and calculate potential energy functions for conformational interchange.
• To compare experimental data with ab initio computational predictions for structural parameters and stability.

Main Methods:

• Variable temperature infrared spectroscopy (-60 to -100 °C) in liquid xenon.
• Ab initio calculations using various basis sets (MP2/6-31G* to MP2/6-311+G**).
• Analysis of infrared spectra, including torsional fundamentals and hot bands.

Main Results:

• Enthalpy difference for propionyl fluoride: 329 ± 33 cm⁻¹ (trans more stable).
• Enthalpy difference for 2-methylpropionyl fluoride: 297 ± 30 cm⁻¹ (gauche more stable).
• Calculated potential functions governing conformational interchange.
• Reassignment of fundamental frequencies based on experimental and computational data.

Conclusions:

• The study provides quantitative data on the conformational stability of propionyl and 2-methylpropionyl fluorides.
• Ab initio calculations support experimental findings and aid in spectral assignments.
• The methodology is applicable to other acyl fluoride compounds.