Standard enthalpies of formation of rubidium and ammonium acetates, and the barrier opposing ammonium ion rotation

Abstract

The correlation between the quantity 1/n{Δ_fH^⊖_m[(NH₄)_nX, s]–Δ_fH^⊖_m[Rb_nX, s]} and the rotational barrier in the ammonium salt has been strengthened by establishing the data point for the acetates. This point lies in a hitherto empty barrier-height region between 25 and 44 kJ mol^–1. It was obtained by determining Δ_fH^⊖_m(CH₃CO₂Rb, s) in a solution calorimeter. The value –722.6 ± 1 kJ mol^–1 agrees very closely with a previously published prediction.