Calculational study of fluoroammonium and related cations and dications.

Structures as well as (15)N and (19)F NMR chemical shifts of a series of fluoroammonium ions were studied by ab initio/GIAO-SCF, GIAO-MP2 and GIAO-CCSD(T) methods. Calculated (15)N and (19)F NMR chemical shifts correlate well with the experimental data. The relative stabilities as well as the charge of the central nitrogen atom of fluoro-substituted tetrahedral ammonium ions were found to increase linearly with the increasing number of fluorine substituents due to their strong electron-withdrawing inductive effect. Similarly the magnitude of (15)N NMR chemical shifts also increase linearly with the increasing number of fluorine substituents in accord with the strong deshielding effect of fluorine. Structures as well as (15)N and (19)F NMR chemical shifts of yet experimentally unknown fluoroammonium dications were also computed.