Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
THE MECHANISM OF RING OPENING AND RING FORMATION REACTIONS OF GAS-PHASE RADICAL CATIONS (MASS SPECTROMETRY, CYCLOBUTENES, PERICYCLIC REACTIONS)
Abstract
In this thesis, we report the mechanism of ring opening and ring closure reactions of gas phase ions of compositions C(,10)H(,12)('+), C(,10)H(,10)('+), C(,10)H(,8)('+), C(,9)H(,7)('+), C(,5)H(,8)('+), and C(,4)H(,6)O('+). The research was conducted by using tandem mass spectrometry and Fourier transform mass spectrometry utilizing collisionally activated dissociation, collisional ionization, unimolecular dissociation, ion-molecule reaction, thermochemical and isotopic labelling techniques. The extent of isomerization of various gas-phase ions was investigated by forming the ions with different energy distributions which was accomplished by employing electron and charge exchange ionization. The results obtained have revealed that one of the consequences of ionization of a molecule is to enhance the rate of pericyclic reactions compared to the corresponding reactions of closed-shell compounds. This is exemplified by the energy advantage gained in the rates of the electrocyclic reactions of phenyl- and methyl-substituted cyclobutene radical cations and cycloaddition of ketene('+) and ethylene. The effects of substitution on the activation energy of ring opening of cyclobutene radical cation were found to be parallel to those of the corresponding neutral molecules. Substitution at the allylic carbon of the cyclobutene radical cation enhances the rate of the ring opening, whereas substitution at the double bond stabilizes it. The ketene radical cation has been shown to react with ethylene. The mechanism is {1+2} cycloaddition across the carbon-carbon double bond forming the cyclobutanone radical cation. The ions derived from acyclic olefins with the double bond out of conjugation with a phenyl group and from strained ring molecules are shown to rearrange to thermodynamically more stable structures. For example, the various C(,10)H(,10)('+) ions rearrange to 3-methylindene ion. Likewise, rearrangements of 1-phenyl-2-butene('+) to 1-methylindan('+) and of benzylcyclopropane('+), 1-phenylcyclobutane('+) and 4-phenyl-1-butene('+) to tetralin('+) occur with ease.
Subject Area
Organic chemistry
Recommended Citation
DASS, CHHABIL, "THE MECHANISM OF RING OPENING AND RING FORMATION REACTIONS OF GAS-PHASE RADICAL CATIONS (MASS SPECTROMETRY, CYCLOBUTENES, PERICYCLIC REACTIONS)" (1984). ETD collection for University of Nebraska-Lincoln. AAI8423775.
https://digitalcommons.unl.edu/dissertations/AAI8423775