Conformational analysis and vibrational assignments of 2,2,3,3-tetrafluoro-1-propanol CHF2CF2CH2OH as three-rotors system

Analysis of vibrational spectra of 3-halo-1-propanols CH(2)XCH(2)CH(2)OH (X is Cl and Br)

The conformational stability and the three rotor internal rotations in 3-chloro- and 3-bromo-1-propanols were investigated by DFT-B3LYP/6-311+G and ab initio MP2/6-311+G, MP3/6-311+G and MP4(SDTQ)//MP3/6-311+G levels of theory. On the calculated potential energy surface twelve distinct minima were located all of which were not predicted to have imaginary frequencies at the B3LYP level of theory. The calculated lowest energy minimum in the potential curves of both molecules was predicted to correspond to the Gauche-gauche-trans (Ggt) conformer in excellent agreement with earlier microwave and electron diffraction results. The equilibrium constants for the conformational interconversion of the two 3-halo-1-propanols were calculated at the B3LYP/6-311+G level of calculation and found to correspond to an equilibrium mixture of about 32% Ggt, 18% Ggg1, 13% Tgt, 8% Tgg and 8% Gtt conformations for 3-chloro-1-propanol and 34% Ggt, 15% Tgt, 13% Ggg1, 9% Tgg and 7% Gtt conformations for 3-bromo-1-propanol at 298.15K. The nature of the high energy conformations was verified by carrying out solvent experiments using formamide ( epsilon=109.5) and MP3 and MP4//MP3 calculations. The vibrational frequencies of each molecule in its three most stable forms were computed at the B3LYP level and complete vibrational assignments were made based on normal coordinate calculations and comparison with experimental data of the molecules.

Solvent dependence of conformational stability and analysis of vibrational spectra of 2,2,3,3,3-pentafluoro-1-propanol

The conformational stability of 2,2,3,3,3-pentafluoro-1-propanol was investigated by the DFT-B3LYP/6-311+G** and the ab initio MP2/6-311+G** calculations. The calculated potential energy curves of 2,2,3,3,3-pentafluoro-1-propanol at both levels of theory were consistent with three distinct minima that correspond to Trans-gauche-gauche (Tgg), trans-trans-gauche (Ttg) and trans-gauche-gauche(-) (Tgg1) conformers in the order of decreasing relative stability. The equilibrium constants for the conformational interconversion of 2,2,3,3,3-pentafluoro-1-propanol were calculated and found to correspond to an equilibrium mixture of about 46% Tgg, 43% Ttg and 11% Tgg1 conformations at 298.15K. The calculated (%Ttg/%Tgg) ratio of 0.93 is consistent with the 0.85 ratio of the observed intensities of the 772 and 794 cm(-1) lines in the Raman spectrum of the liquid. The nature of the high energy Ttg conformation was verified by solvent experiments using formamide (epsilon = 109.5) and acetonitrile (epsilon = 37). The vibrational frequencies of the molecule in its 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.

Three rotor potential energy scans, conformational equilibrium constants and vibrational analysis of 3-fluoro-1-propanol CH(2)FCH(2)CH(2)OH

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 298.15K. 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.