Gauche preference of β-fluoroalkyl ammonium salts.

The strong gauche preference along with the F-C-C-N(+) fragment in 3-fluoropiperidinium cation and analogues, in the gas phase, is dictated by electrostatic interactions, which can be both hydrogen bond F···H(N(+)) and F/N(+) attraction. In aqueous solution, where most biochemical processes take place, electrostatic effects are strongly attenuated and hyperconjugation is calculated to be at least competitive with Lewis-type interactions.