Polarization effects on the electronic structures of organic reactive intermediates
Abstract
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.
Degree
Ph.D.
Advisors
Wenthold, Purdue University.
Subject Area
Chemistry|Organic chemistry
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