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. T he energies of the conformations of FE, its methyl ether, cis-2-fluoro cyclohexanol (4) and its methyl ether (5) were investigated by molecul ar mechanics (MMPMI) calculations, FE and its methyl ether were invest igated by ab initio calculations (MP2/6-31++G*//MP2/6-31++G**). The r esults were all consistent with a dominance (> 90%) of the gauche rota mer 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 G g' the most important one. However, from the conformations of the meth yl ethers 1-fluoro-2-methoxyethane and 3 it was concluded that an intr amolecular hydrogen bond was not important for this dominance. Other i nteractions, e.g. the repulsive forces between the lone pair electrons of the oxygen atom and the fluorine atom, were found to be more impor tant than a hydrogen bond for the conformational composition around th e C-O bond. The rotamer distribution around the CH2CH2 bond was found to be the result of the gauche effect.