An NMR study of the conformational equilibrium of 5‐fluoro‐1,3‐dioxan in solution. Dependence on solvent

The 1 H and 19 F NMR parameters of 5‐fluoro‐1,3‐dioxan ( 1 ) dissolved in a number of solvent systems are interpreted on the basis of fast inversion between two chair conformations. In cyclohexane solution the two chair conformations are almost equally populated, whereas in more polar solvents, such as chloroform, the conformation having the fluorine substituent in an axial position is strongly preferred. Addition of acetic acid to a solution of 1 in cyclohexane increases the preference of the fluorine substituent for the axial orientation. Possible reasons for these observations are discussed.