The photosolvolysis of a series of hydroxy-substituted benzyl alcohols (ArCH₂OH) has been studied. Photomethanolysis of these alcohols showed exceptionally higher efficiencies for methyl ether formation (in 1:1 H₂O-MeOH) than the corresponding methoxybenzyl alcohols. UV-Vis absorption spectra of photogenerated transients were recorded in aqueous solution and had similar appearance to the carbocations that are observable from the methoxybenzyl alcohols, but with much longer lifetimes. These transients were also observable in neat organic solution for the ortho isomers. The yields of all these transients increased with increasing water content. The highest yields were observed in basic aqueous solution when pH > pKₐ(S₀) (of the phenol moiety). In addition, photolysis of the appropriate coumaranones gave the same transient absorption as that from the corresponding o-hydroxybenzyl alcohols. Since photolysis of coumaranones are known to give o-quinone methide, (o-QM) intermediates (via loss of CO), the transients observed for the o-hydroxybenzyl alcohols are assigned to o-QMs. The transients observed for the m and p-isomers are assigned to the corresponding m and p-QMs. The quantum efficiencies for QMs generation from hydroxybenzyl alcohols are in the order as o > m >> p, in agreement with Zimmerman's orthoctivation theory. The mechanism proposed at pH < pKₐ(S₀) involves adiabatic deprotonation of the ArOH moiety in the first excited singlet state (S₁) followed by heterolytic cleavage of the C-O bond of the hydroxymethyl group. In basic media, direct excitation of the phenolate ion results in the loss of hydroxide ion to generate QMs. Subsequent nucleophilic trapping of these QMs by solvent results in the observed solvolysis product. o-QMs were also generated in neat organic solution. The proposed mechanism involves adiabatic deprotonation of phenol moiety facilitated by either intermolecular or intramolecular hydrogen bonding with a benzylic OH group. This Thesis has demonstrated that a simple and general method is available for the photogeneration of all the QM isomers. Notably, the method is applicable to m-QMs, which have previously required more elaborate methods for their generation. A polymerization reaction of m-QMs has been discovered in basic media during investigations of their chemistry. / Graduate

Hydrozirconation and subsequent phosphination have been developed into a versatile synthetic methodology leading to formation of phosphorus-carbon bonds. A family of phosphinoalkylsilane ligand precursors SiHMen(CH₂CH₂CH₂PPh₂)₃₋n (ChelH, I: n = 2; biPSiH, II: n = 1; triPSiH, III: n = 0) previously prepared via a photo-chemical route were synthesized in this way and the phosphination step has been shown to be dependent on steric factors. Similar methods have been used to obtain a group of new ligand precursors, the poly(silaalkyl)phosphines PPhn(CH₂CH₂CH₂PR₂)₃₋n (12: n = 1; 13: n = 0), which have been isolated and fully characterized. Analogues PPhn(o-C₆H₄SiMe₂H)₃₋n (21 : n = 1; 22: n = 0) containing more rigid benzylic backbones have been prepared from the corresponding (o-tolyl)phosphines via polylithiation and shown to exhibit temperature dependent NMR behavior. Poly(silaalkyl)phosphine coordination chemistry has been explored, yielding an unprecedented trans-bis(silyl) Pt(II) complex Pt[PhP(o-C₆H₄CH₂SiMe₂)₂]PPh₃ (25 ) which was isolated and characterized by using spectroscopic methods. The chemistry of [bis(diphenylphosphinopropyl)silyl] hydrido dicarbonyl ruthenium(II), RuH (biPSi)(CO)₂ (26), has been investigated in detail. The two diastereomers, syn and anti, were observed to exchange slowly with the two CO groups also scrambling at a comparable rate. A kinetic study of these two intramolecular isomerization processes suggests the involvement of dissociation and re-association of the chelate (biPSi) phosphines. Oxygen atom insertion into the Ru-Si bond of 26 occurs both in a hydrolysis process and direct oxidation by dioxygen. A labeling experiment suggests the former may involve a molecular dihydrogen intermediate, while the latter leads to insertion of oxygen atoms into both Ru-Si and Si-C bonds. Chlorination of 26 and subsequent thermal loss of a CO group afforded a novel l6e five coordinate Ru(II) species RuCl(biPSi)(CO) (42). Reaction of 42 with NaBH₄ or LiAlH₄ gave a mononuclear borohydride complex Ru(biPSi)(CO)(μ-η²-H₂BH₂) (43) or a rare hydrido anionic complex [fac-Ru(H)₂biPSi)(CO)]⁻ (44), both of which are extremely sensitive and have been identified in situ by using solution NMR spectroscopy. The silyl group in 26 was found to exert a stronger trans effect than hydride. / Graduate

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The object of the present work was the investigation of two separate topics, the investigation of the radical-radical termination step in the photochemical oxidation of acetaldehyde and the investigation of the photolysis of crotonaldehyde, both in the gas phase and at room temperature. A third topic, the photolysis of 3-butene-1-al, was investigated in the course of the work, in order to provide evidence in favour of the mechanism proposed for the photolysis of crotonaldehyde. In the first part of the work, mixtures of acetaldehyde and isotopically enriched oxygen containing argon as a reference gas were irradiated at 25°C with light at a wavelength of 3130 [formula omitted] and the reaction products were analyzed by gas chromatography and mass spectrometry. The major products were found to be peracetic acid and diacetyl peroxide. By following the rate of formation of these products, as well as the concentrations of the three possible kinds of oxygen in the reaction mixture, it was possible to verify McDowell and Farmer's mechanism for the photooxidation of acetaldehyde and establish a satisfactory mechanism for the chain terminating step of the reaction. In the second part of the work, crotonaldehyde was irradiated at 30°C with light at a wavelength of 2450-4000 [formula omitted], and the products analyzed by gas chromatography and infra-red spectroscopy. The only product in experiments of short duration was found to be 3-butene-1-al, thus establishing isomerization as the primary process of the reaction. In later stages CO, propylene and 1,5-hexadiene were formed. The following experimental laws were found to hold for the rate of formation of these products: d(3-butene-1-al)/dt = ႴIabs , Ⴔ = 0.095 ± 0.005 d(1, 5-hexadiene)/dt ∼ (Iabs².t)/(crotonaldehyde ) d(propylene )/dt ∼ (Iabs².t)/(crotonaldehyde)1.3-1.5 No detailed law was established for the rate of formation of CO, but whenever measured it was found to follow closely the propylene formation. These experimental laws were interpreted by means of a mechanism, in which crotonaldehyde participates in so far as it isomerizes to 3-butene-1-al. The latter was assumed to yield the three other products of the reaction through a mixed radical-molecular photochemical dissociation. Evidence was provided in favour of the proposed mechanism by studying the photolysis of 3-butene-1-al at 30°C and a wavelength of 2450-4000 [formula omitted]. The products of the reaction were found to be propylene, 1,5-hexadiene and CO, with their rates of formation obeying the following laws: d(1,5-hexadiene)/dt = Ⴔhexad. Iabs , Ⴔhexad = 0.135 ± 0.0318 d(propylene)/dt = Ⴔprop‧Iabs , Ⴔprop = 0.79 ± 0.05 CO formation was found to be approximately equal to propylene formation. These experimental laws were interpreted by means of a mixed radical-molecular photochemical dissociation of 3-butene-1-al, thus justifying the mechanism proposed for the photolysis of crotonaldehyde. / Science, Faculty of / Chemistry, Department of / Graduate

The photolysis of nitrate esters in solution or in thin solid films occurred readily in the 2650 to 3340 A spectral region. In the presence of diphenylamine, phloroglucinol or hydroquinone, the photoreaction yielded colored products that gave a measure of the extent of the reaction. The most effective wavelength for formation of yellow products from diphenylamine was at 2890 A. Irradiation of ethanol or benzene solutions 0.02 M in diphenylamine and l,4;3,6-dianhydro-D-glucitol-2,5-dinitrate (isosorbide dinitrate), followed by chromatographic separation, gave six organic compounds, two of which were isolated in pure form by adsorption chromatography and identified as 2- and 4-nitrodiphenylamine. Two other colored products were tentatively identified as N-nitroso- and p-nitrosodiphenyl-amine; no trace of the unreacted nitrate ester could be detected. Photolysis of isosorbide dinitrate alone in ethanol solution caused a weight loss of 17.7% in 21 hours and the formation of an unidentified hydrophilic, colorless sirup. A similar product was obtained on irradiation of an anhydrous benzene solution of the dinitrate. Possible mechanisms of the photolysis are discussed. / Science, Faculty of / Chemistry, Department of / Graduate

Previous research on the photolysis of ketene has shown that the kinetics of photodissociation processes were not fully understood and that more accurate data were needed to evaluate the mechanism of the rate of dissociation of the electronically and vibrationally excited molecules. There was some evidence that the primary quantum yields at shorter wavelengths extrapolated to a value greater than unity at zero pressure, if this were not within experimental error, it would provide evidence for a process of multistage deactivation of the excited ketene molecules. In the kinetic studies of the dissociation of excited molecules, intersystem crossing to the triplet state had been included to account for phosphorescence. Theoretical consideration from this had led to predictions of the effect of dissociation from the triplet state on the quantum yields of carbon monoxide on the photodissociation of ketene. Experimental verification was now needed to determine the effect, if any, derived from triplet dissociation. Previous attempts have been made to apply the unimolecular theory of dissociation to the photodissociation of excited molecules, but the data available yielded physically impossible results. Hence, only reasonable theoretical values of the parameters involved are given. This research attempted to obtain more accurate data on the quantum yields of ketene at 3130 Å, 3340 Å and 3650 Å at various temperatures. From the results it is now possible to differentiate within the limits of the experiment, between the various theories of the dissociation process. It is established that triplet dissociation is either not a real effect or is small enough to be undetectable under the experimental conditions. It is possible to discount a theory of a cascade collisional deactivation process involving more than three collisions of the excited molecules, but differentiation is not made between one, two and three collisions under experimental conditions. The unimolecular theory of dissociation is applied to the results of the photodissociation process and values determined for the parameters involved. Reasonable agreement with the theoretical predictions is obtained. / Science, Faculty of / Chemistry, Department of / Graduate

The object of this work was the investigation of the photochemical oxidation of formaldehyde in the gaseous phase at 110°C. Reaction mixtures, where the O2: CH₂O ratio was approximately 1:10, were irradiated with ultra violet light at a wavelength of 3130A⁰ and the reaction products analyzed. The major products were found to be CO, H₂ and HCOOH. CO₂ was a minor product. No peroxides were found and the reaction was oxygen independent at low O₂:CH₂O ratios. The formation of the major products was found to be directly proportional to the initial formaldehyde pressure and to the intensity of the absorbed light. A satisfactory mechanism is proposed to explain the formation of the reaction products, and the following kinetic equations were derived: [formula omitted] / Science, Faculty of / Chemistry, Department of / Graduate

The production of vibrationally excited oxygen, O*₂, following the isothermal flash photolysis of C10₂, C1₂O and of the C10 free radical has shown to be due to the reactions of oxygen atom with C10₂ and C10 (1, 2). In both reactions, the energy, distribution in the products is markedly non-equilibrated with a large fraction of the energy liberated in the form of vibrational excitation of the oxygen molecule. The highest level of O*₂ produced corresponds to the exothermicity of the reactions. The rate constants for the production of O*₂ in levels v'’ = 6 ➛ v’’ = 13 are approximately equal. The relaxation of 0*₂ by C10₂, C10 and by C1 and 0 atoms has been studied and the exceptional efficiency of the atoms demonstrated. The rate constant for the bimolecular reaction of C10 radicals (10) was measured using C10₂, C1₂/0₂, C1₂0, C1₂0/C1₂ as sources of the radicals. The constancy of the value of 2.7 ± 0.3 x 10⁷ 1 mole⁻¹ sec⁻¹ obtained from all systems contrasts with the literature values of 6.2 x 10⁷ 1 mole⁻¹ sec⁻¹, 4.8 x 10⁷ 1 mole⁻¹ sec⁻¹ and 2.4 x 10⁷ 1 mole⁻¹ sec⁻¹, obtained from the first three systems. The chlorine and bromine photosensitised decomposition of C10₂ and C1₂0 have been studied and the extinction coefficient of C10 and BrO free radicals measured. Mechanisms have been proposed for all systems and all relevant rate constants have been measured. The results are listed below. [formulas omitted] / Science, Faculty of / Chemistry, Department of / Graduate

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