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Title: Stereochemical and trapping studies of biradicals
Author: Edmunds, Andrew John Francis
ISNI:       0000 0001 3438 3597
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1986
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The work in this thesis can be divided into two parts. 1) Stereochemical studies Irradiation of cis-anti-5,6-[2H]2-2,3-diazablcyclo[2.2.2]oct-2-ene (dg-DBO) leads to bicyclo[2.2.0]hexane (BCH) in which the deuterium is predominantly exo, i.e. double inversion of configuration, and hexa-1,5-diene (HD) with equal amounts of cis and trans deuterium. In addition, direct photolysis affords small amounts of cyclohexene formed via a stereoselective 1,3-shift. The proportions of EE-, EZ-, and ZZ-d2-HD’s were not accessible by direct spectroscopic methods but could be obtained by a chemical method combined with mass spectrometry. Stereoselective substitution at the 1,6-positions, in which Z-deuterium was lost and E- deuterium retained, translated stereochemical information into deuterium content. The results of the analysis showed that the EZ-isotopomer was formed predominantly, but significant amounts of EE- and ZZ-isotopomers were also present. The results are compared to the pyrolysis stereochemistry of stereoselectively labelled d2-BCH and the known stereochemistry for the deazetation of DBO. A mechanism is proposed that accounts for all the observations. 2) Trapping studies While triplet biradicals have been intercepted by a wide range of biradical traps only one case of singlet biradicals, 2-alkylidenecyclopentane-l,3- diyls, are sufficiently long-lived to undergo intermolecular reactions. Related singlet biradicals have been proposed as intermediates in the photochemical rearrangement of a cyclic triene, 6-methylene-3,3- dimethylcyclohexa-1, 4-diene. When the triene was irradiated in the presence of olefins, 1:1 triene:olefin adducts could be isolated. Their structure was established by X-ray diffraction, spectroscopy, and independent synthesis. The mechanism of their formation is discussed.
Supervisor: Not available Sponsor: Science and Engineering Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry