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The Kinetics of the reactions involving alkyl and silyl hydrides were studied by the flash photolysis / resonance fluorescence technique. The reactions of alkyl radicals (R = C₂H₅, i-C₃H₇, t-C₄H₉) with HBr have been studied at room temperature and the rate constants obtained (units are in cm³ s^-1 ) are: k₃.₃ = (7.01 ± 0.15) x 10^-12, k₃.₂ = (1.25 ± 0.06) x 10^-11, k₃.₁ = (2.67 ± 0.13) x 10^-11 These results, combined with previously determined reverse rate constants and other kinetic information, yield bond dissociation enthalpies (units in kJ mol^-1) at 298 K : primary C-H in C₂H₅-H (423.6 ± 2), secondary C-H in i-C₃H₇-H (409.9 ± 2), tertiary C-H in t-C₄H₉-H (405.1 ± 2). These rate constants and bond energies are in good agreement with previous results.

<p> This thesis presents a study of the roles of ligands on silicon in two parts.</p> <p> In Part A, the relationship between the β-effect - the ability of a silyl group to stabilize a carbocation β to silicon, and the electron-withdrawing ability of the ligands on silicon was examined. The bromination of a series of (E)-β-silylstyrenes was chosen as a way to quantify the β-stabilization. The degree of syn-addition of bromine to (E)-β-silylstyrene was used as a measure of the stabilizing ability of the silyl group.</p> <p> The bromination of a series of four (E)-β-silylstyrenes was investigated [ligands on silicon: (SiMe3O)3; (CH3COO)3; (CCl3COO)3; (CF3COO)3]. It was found that the degree of syn-addition decreases as the silyl group electronegativity increases. Combined with the results previously obtained in our lab, two linear relationships between the degree of syn-addition and the silyl group electronegativity were observed in two groups of (E)-β-silylstyrenes [Group A, ligands on silicon: Me3-nXn, n = 1-3, X= Cl, F and (MeO)3; (Me3SiO)3 and Group B, (CH3COO)3; (CCl3COO)3; (CF3COO)3; (p-MeOPhO)3; (PhO)3; (p-ClPhO)3]. The degree of syn-addition was found to be more sensitive towards the group electronegativity for compounds in Group B. It was also found that, as the group electronegativity increases, the α-SiCH 1H and 29Si NMR chemical shifts of compounds in Group A decrease. In contrast, the α-SiCH 1H and 29Si NMR chemical shifts of compounds in Group B tend to increase.</p> <p> In Part B, a series of hydrosilanes were studied and their reactivities in iodination were found to be in the order: CH3SiH(OEt)2 > PMHS > CH3SiHCl2.</p> <p> The behavior of these organosilicon compounds is discussed in terms of the structural features of the silyl groups - the ligands on silicon.</p> / Thesis / Master of Science (MSc)

Six bis(silyl)acetylenes with the following varied silicon substituents were prepared: I (Me, Me); II (H, H); III (Cl, H); IV (Cl, Cl); V (OMe, H); VI (OMe, OMe). While I and II may be prepared by the reaction of dilithio- or bis(bromomagnesium)-acetylide with appropriate chlorosilane, similar reactions designed to give III - VI give oligomers, YMe_2Si(C≡C-SiMe_2)_nY, VII, Y = Cl, OMe, as the major products indicating that the acetylenic functionality on silicon activates the chlorosilane toward nucleophilic substitution. Compounds III and IV were prepared by free radical chlorination of II. Methanolysis of III and IV gave quantitative yields of V and VI, respectively. In the presence of mineral acid, VI readily cyclized to give high yields of the cyclic siloxane octamethyl-4,9-dioxa-3,5,8,10-tetrasila-cyclodeca-1,6-diyne, VIII, and the analogous triyne, IX. It was determined that V and VI could be prepared directly from II in high yield by methanolysis with palladium catalyst. Vaska's complex also accomplished the conversion. I attempted to prepare bis(ethoxydimethylsilyl)acetylene by using of Wilkinson 's catalyst for hydrosilylation with acetaldehyde. The principal product of this reaction was 1-(dimethylsilyl)-3,5,5-trimethyl-4-oxa-3-silacyclopent-1-ene, XI.