This Thesis consists of six Chapters, and covers ketene reactions with the nitroxyl radical 2,2,6,6-tetramethylpiperidinyloxyl (Tempo, TO·) and the reactivity of the adducts formed. The objective of this study has been the elucidation of the chemistry of these adducts, which is a subject of broad interest because of the importance of the thermal dissociation of nitroxyl radicals in living free radical polymerization. As a result of observations made during the course of this work the studies of the reactivity of esters of 2,2,6,6-tetramethyl-N-hydroxylpiperidine and of radical cyclization during the acyloin reaction of unsaturated esters were also undertaken.Chapter Four reports the thermolysis of N-tetramethylpiperidinyl triphenylacetate where the rate and product studies indicate the reaction proceeds by a concerted homolytic formation of triphenylmethyl and tetramethylpiperidinyl radicals.Chapter One presents a brief background to nitroxyl radicals and especially Tempo with emphasis on its wide applications.A different approach to 5-hexenyl radical cyclization is examined in Chapter Three through the acyloin condensation. The cyclization of 5-hexenyl radical was achieved via acyloin intermediate when the double bond was activated with a phenyl substituent.Chapter Five examines Tempo-esters which are found to react upon thermolysis in the presence of the solvents such as chloroform or toluene that are capable of hydrogen atom donation by induced decomposition processes forming carboxylic acids, tetramethylpiperidinyl radicals, and solvent derived radicals. The large solvent isotope effects k(PhCH3)/ k(PhCD3) and k(CHCl3)/ k(CDCl3), the observed products, and the significant rate acceleration caused by better H-atom donors such as 2,6-di-tert-buty1-4-methylphenol (BHT) and 2,2,6,6-N-tetramethylpiperidinol (TOH) provide evidence for induced decomposition mechanism.An ionic mechanism was observed in solvolysis of N-tetramethylpiperdinyl para-nitrobenzoate forming 2,2-dimethylpyrrolidine by rearrangement of an incipient 2,2,6,6-tetramethylpiperidinyl derived nitrenium ion (Chapter Six).In Chapter Two the thermal reactivity of adducts formed by the addition of two Tempo molecules to 4-pentenylketenes was carried out. The alpha-enolate radicals formed from the ketenes underwent successful 5-exo cyclization in t-butanol at 130--135°C.