Observation and electronic properties of reactive intermediates from measurement and electronic structure calculations

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Date
2018
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University of Alabama Libraries
Abstract

Electronic structure calculations were performed to understand the properties of reactive intermediates generated from experiment. Aluminum, manganese and iron nitrate anions were generated in the gas-phase via electrospray ionization (ESI) and were observed to decompose into metal oxides under collision induced dissociation (CID). Aluminum-oxygen bonds were formed after each consecutive loss of NO2•, which possess significant radical character localized to the oxygen ligands. These oxygen radicals facilitate the decomposition of Al(NO3)4- by abstracting neutral oxygen atoms and then undergoing loss of O2. Neutral oxygen atom abstraction was also observed in the decomposition of Mn(NO3)3-, however loss of NO• occurs immediately after, resulting in the rearrangement of a nitrate ligand to provide two oxygen substituents. Both MnO(NO3)2- and MnO2(NO3)- were observed to decompose under CID into the permanganate anion, MnO4-, which occurs through a pair of spin forbidden surface crossings. Fe(NO3)4- can also decompose into a tetroxide, FeO4-, however this occurs through 4 consecutive losses of NO2•, and no nitrate ligand rearrangement was observed. Oxidation of the metal center continues until MnO4- and FeO4- exist in the +VII oxidation state. Density functional theory (DFT) was used to optimize the structures for the ions and neutrals generated by ESI, and coupled cluster methods were used to calculate accurate electronic energies. DFT studies were also performed to interpret the emission spectrum of the 4-methyl-3-azabenzyl radical which was generated in a corona excited supersonic expansion source to understand how substituting a nitrogen atom into the benzene ring can change the electronic properties of aromatic radicals. Although it is possible for an electron in the nitrogen lone pair to be promoted via a charge transfer excitation, the observed emission spectrum of the 4-methyl-3-azabenzyl occurs from an unpaired electron relaxing from an antibonding orbital in the π system to a p orbital localized on the CH2 substituent. Several vibrational energies were measured and the calculated energies agree with experiment.

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Electronic Thesis or Dissertation
Keywords
Chemistry
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