Molecular orientation around the fluoride ion dissolved in methanol and formamide

Abstract

The ¹⁹F nuclear magnetic relaxation times of solutions of RbF in CH₃OH and in the isotope-labelled methanols CH₃OD and CD₃OH have been measured as a function of the salt concentration. Evaluation by standard methods involving the expression for the intermolecular rates yields the F^––CH₃ and F^––OH distances. The same procedure for F^– in the formamides HCONH₂, DCONH₂, HCOND₂ and CDOND₂ yields the F^––H and F^––H₂N distances. Knowledge of the geometry of the molecule then allows the determination of the orientation relative to F^–. In methanol we find an H-bonding orientation and in formamide a compromise between H-bonding and dipole alignment.