GAS-PHASE PROTONATION OF ARYLALKYLAMINES - A METASTABLE ION STUDY

The unimolecular metastable decompositions of protonated arylalkylamin es of general formula (RRC6H3CHR3)-R-1-C-2(CH2)(n)(NRR5)-R-4 where R-1 = H or OH; R-2 = H, F, NO2, OH Or OCH3; R-3 = H Or OH; R-4 and R-5 = H and/or CH3; and n = 1-3, generated by chemical ionization with water and ammonia as ionizing reagents, have been examined via the analysis of the mass-analysed ion kinetic energy spectra of the protonated mol ecules. The mechanisms proposed have been probed by chemical ionizatio n of the deuterated analogues of the amines with D2O and ND3, The resu lts show that protonation occurs preferentially on the amino group lea ding to abundant ions due to ammonia (or amine) loss, although ions re sulting from transfer of the proton from the amino group to the aromat ic ring, to the hydroxy group para to the aliphatic chain and to the b enzylic OH, are also observed, Experimental evidence for H/D exchange between the deuteronated amino group and the aromatic ring is presente d, and discussed in terms of the internal energy content of the deuter ated ions and structural features of the amines, such as aliphatic cha in length and the presence of a second hydroxy group on the aromatic r ing. (C) 1998 John Wiley & Sons, Ltd.