IPSO reaction studies of aromatic systems
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The first section of this thesis is concerned with exploring the mechanism of reaction with nitrogen dioxide of a series of unsymmetrically substituted phenols and their derived 4-nitrocyclohexa-2,5-dienones. The effect the substituents have on the regioselectivity of NO₂ reaction on the phenols is examined by analysis of the types of products and in the case of 2,3,4,6-tetramethylphenol (32) it was possible to undertake 15N-labelling studies to unambiguously ascertain the mode of reaction of NO₂. It is shown that the regiochemistry is dependent on the electron withdrawing or electron donating nature of the 3-substituent in the series of phenols studied, specifically 4-chloro-2,3,6-trimethylphenol (31) 2,3,4,6-tetramethylphenol (32) and 3-chloro-2,4,6- trimethylphenol (33). The second section of this thesis is concerned with examining the reactions of 1,4,5,8-tetramethylnaphthalene (21), 1 ,8-dimethylnaphthalene (37), 1-methylnaphthalene (59) and as described in Appendix I the reaction of benzene with tetranitromethane in the presence of light as an activating source to generate the charge transfer complex. The photoaddition of tetranitromethane to aromatics has been shown to give nitro/trinitromethyl, nitrito/trinitromethyl, and hydroxy/trinitromethyl adducts. Also observed were some nitro or hydroxyl cycloadducts in which a nitro group formally associated with a trinitromethyl group is involved in a thermal 1,3-dipolar addition across an alkene system. Tetranitromethane in the presence of an aromatic system and light (≥435 nm) fragments to a trinitromethanide ion (O₂N)₃C-, •NO₂ while the aromatic transfers an electron in the charge transfer process to generate a radical cation. The radical cations are then attacked initially by the very reactive trinitromethanide ion and secondly by •NO₂. This gives rise to the formation of a variety of adducts. The nature of the radical cation is crucial in determining the position of attack of the trinitromethanide ion. In conclusion this work has shown that the relative atomic charges of the aromatic radical cations are important in making an assessment of the likely site(s) of the trinitromethanide attack on that radical cation, but that steric interactions with ipso, peri and vicinal substituents to the reaction site may dictate the overall course of the reaction. Throughout the thesis extensive use is made in product structure determination of single crystal X-ray analysis and in all 23 crystal structures are presented.