Three rotor potential energy scans, conformational equilibrium constants and vibrational analysis of 3-fluoro-1-propanol CH₂FCH₂CH₂OH

The conformational stability and the three rotor internal rotations in 3-fluoro-1-propanol were investigated by the DFT-B3LYP/6-311 + G** and the ab initio MP2/6-311 + G** levels of theory. The calculated potential energy curves of the molecule at both levels of theory were consistent with complex conformational equilibria of about 12 minima, all of which were predicted to have real frequencies at both the B3LYP and the MP2 levels. The lowest energy minimum in the potential curves of 3-fluoro-1-propanol was predicted to correspond to the Gauche-gauche-trans (Ggt) conformer in excellent agreement with microwave and electron diffraction results. The equilibrium constants for the conformational interconversion of the molecule were calculated and found to correspond to an equilibrium mixture of about 33% Ggt, 14% Ggg1 and 13% Gg1g and about 43% Ggt, 12% Ggg1 and 10% Gg1g distribution by the B3LYP/6-311 + G** and the MP2/6-311 + G** calculations, respectively, at 298.15 K. The vibrational frequencies of each molecule in its three stable forms were computed at B3LYP level and complete vibrational assignments were made based on normal coordinate calculations and comparison with experimental data of the molecule.