Nucleophilic identity substitution reactions. The reaction between ammonia and protonated amines

Abstract

The gas phase reactions between NH₃ and the protonated amines MeNH₃⁺, EtNH₃⁺, PrⁱNH₃⁺, and Bu^tNH₃⁺ have been studied by high level ab initio methods. Mass spectrometric experiments yielded no significant reaction products; this result being consistent with the calculated reaction barriers. The potential energy profiles for both nucleophilic substitution (S_N2) and elimination (E2) pathways have been investigated. Both back side Walden inversion (S_NB) and front side (S_NF) nucleophilic reaction profiles have been generated. The S_NB reaction barriers are found to be higher for the more alkyl substituted reaction centres. Reaction barrier trends have been analysed and compared with the results of a similar study of the H₂O–ROH₂⁺ system (R = Me, Et, Prⁱ, and Bu^t).