Chemistry in nanodroplets: Studies of protonation sites of substituted anilines in water clusters using FT-ICR

Water clusters of protonated substituted anilines generated by an electrosp ray ion source have been investigated using a-Fourier Transform ion cyclotr on resonance mass spectrometer; It is observed that evaporation kinetics an d cluster distributions are highly dependent on sites of protonation in the substituted anilines.-Based on the examination of the water cluster distri butions of protonated aniline derivatives, the site of protonation is postu lated to be the amine group for aniline, p-anisidine, p-thiomethylaniline; p-ethylaniline, and m-ethylaniline. The water cluster distributions of thes e compounds display magic number clusters ([M + nH(2)O](+)) for n = 20, 21; 50, and 52. However there is no indication of clusters with special stabil ity for m-anisidine and m-thiomethylaniline, suggesting that these compound s protonate on the ring. DFT calculations have been performed to obtain pro ton affinities for the different sites of protonation in the substituted an ilines and are in good agreement with experimental observation.