| This thesis was concerned primarily with determining the factors affecting the site of cation attachment and the dissociation of ions in a Quadrupole Ion Trap Mass Spectrometer (QIT). Steric effects are well-known in solution, but are often overlooked in gas-phase chemistry. Use of a novel, adjustable, probe cation allowed for quantitative evaluation of steric inhibition of cation attachment for a series of pyridines. In addition, functional group interactions were found to have a large effect on the gas-phase chemistry of three positional isomers: ortho-, meta-, and para-aminobenzoic acids. Not only did ortho-aminobenzoic acid prove to be ca. 7 kcal/mole more basic than the other isomers, it also formed the greatest abundance of the addition-elimination product from reaction with methoxymethylene cation. Collisionally-activated dissociation (CAD), when combined with such chemically-selective reagent ions such as methosymethylene ion, permitted isomer distinction, not only of these three aromatic positional isomers, but also of diacid and diester regioisomers such as dimethyl maleate and dimethyl fumarate. This combination of techniques also allowed for determination of the site of cation attachment in nicotinoid compounds. The site of ionization is an essential piece of information required for structure elucidation. Gas-phase methylation with trimethyl oxonium showed preference for alkylation on the pyridine nitrogen (N), while methylation reactions in solution (using methyl iodide) showed dominant pyrrolidine nitrogen (N... |
