Polarization effects on the electronic structures of organic reactive intermediates

This dissertation focuses on the study of gas-phase organic reactive (often radical) intermediates using flowing-afterglow mass spectrometry, and mainly includes the study of pyridynes (diradicals having the formula C 5H3N) and aromatic nitrenes. The gas-phase enthalpy of formation of 2,3-, 2,4-, and 3,4-pyridyne were determined using a thermochemical cycle and by measuring the proton affinity and chloride bond dissociation energy of deprotonated 2- and 3-chloropyridine. These results agree well with theoretical calculations and are compared to benzynes and their aromatic precursors (pyridine and benzene). It was found that polarizing effects stabilize 2,4-pyridyne compared to m-benzyne and destabilize 2,3-pyridyne compared to o-benzyne.;Using ion-molecule reactions and measured rate constants, the electronic structure of a series of phenylnitrenes (triplet diradical, Ph-N) with anionic substituents as well as deprotonated benzaldehyde imines (singlet, PhCHN) with neutral substituents were characterized. Introducing strong anionic pi-donors (CH2- and O-) to phenylnitrene stabilizes the closed-shell singlet by more than 30 kcal/mol, such that it becomes the ground electronic state (or degenerate with the triplet) which then resembles a deprotonated imine. Conversely, addition of a strong pi-withdrawing group (-NO2) to deprotonated benzaldehyde imine induces the opposite effect, stabilizing the triplet, nitrene-like state, to the point where it is the ground state. These complementary approaches show that the nitrene/imine character is based upon the spin-state of the ion and can be "tuned" by using appropriate substitution of strong pi-donating/withdrawing groups. Also included is preliminary research on the hydride donation chemistry of benzaldimides and the formation of dithioformic acid in the reaction of benzaldimides and CS2.