THE CONFORMATION OF 2-FLUOROETHANOL - IS INTRAMOLECULAR HYDROGEN-BONDING IMPORTANT

The conformations of 2-fluoroethanol (FE) and trans-4-tert-butyl-cis-2-fluorocyclohexanol (1) have been investigated by FT-1 R and H-1 NM R spectroscopy and the methyl ether of 1 (3) by C-13 NMR spectroscopy. The energies of the conformations of FE, its methyl ether, cis-2-fluorocyclohexanol (4) and its methyl ether (5) were investigated by molecular mechanics (MMPMI) calculations, FE and its methyl ether were investigated by ab initio calculations (MP2/6-31++G**//MP2/6-31++G**). The results were all consistent with a dominance (> 90%) of the gauche rotamer around the CH2CH2 fragment in FE. Furthermore, the gauche rotamer around the CH2OH bond of FE with the hydroxyl proton pointing towards the fluorine atom was also a major component making the conformation Gg' the most important one. However, from the conformations of the methyl ethers 1-fluoro-2-methoxyethane and 3 it was concluded that an intramolecular hydrogen bond was not important for this dominance. Other interactions, e.g. the repulsive forces between the lone pair electrons of the oxygen atom and the fluorine atom, were found to be more important than a hydrogen bond for the conformational composition around the C-O bond. The rotamer distribution around the CH2CH2 bond was found to be the result of the gauche effect.