Gas-phase reactions of nucleophiles with α,β-unsaturated nitriles

Abstract

Gas-phase reactions of nucleophiles with a number of α,β-unsaturated nitriles were studied in a high-pressure negative ion chemical ionization (NICI) source. Both weak and strong nucleophiles react with these molecules giving rise to adduct ions. Under NICI conditions using Cl − and Br − ions the spectra show predominantly M −· and [M + Cl] − or [M + Br] − ions formed by hydrogen bonding. In the hydroxy compounds, [M − H] − is predominant instead of M −·. With stronger nucleophiles, such as MeO − and CH 2CN −, deprotonation competes with adduct formation and electron attachment. The adduct ions observed are [M + MeO] −, [M + O − H] −, [M + CH 2CN] − and [M + CN − H] −. These ions are absent in the saturated nitriles suggesting that unlike the weak nucleophiles, Cl − and Br −, stronger nucleophiles, such as MeO − and CH 2CN −, form adduct ions by covalent bonding with the α,β-unsaturated system. A ring substitution by CN − is suggested for the formation of [M + CN − H] − ions. Deuterium- and 13C-labelled nitriles were also used in this study.