A DFT study on the origin of the fluorine gauche effect in substituted fluoroethanes

DFT derived conformational energy profiles of a series of 2-substituted fluoroethanes (F-CH2CH2-X) have been explored relative to 1,2-difluoroethane, a compound which exhibits a gauche preference. Steric, electrostatic and NBO interactions were explored. In the event the gauche preference for 1,2-difluoroethane is largely hyperconjugative in origin, whereas the conformational preference for the remaining structures is most reasonably explained as a balance between hyperconjugative, steric and electrostatic effects.