The [2,3]-sigmatropic rearrangement is a pericyclic reaction of great synthetic utility to organic chemists. Within the scope of this reaction exist some cases in which the product corresponding to a [1,2] rearrangement is formed, despite the fact this is a forbidden process. Generally this is explained by a radical dissociation-recombination pathway; however, studies into the failure of transition state theory and the necessity to incorporate dynamic effects into mechanistic theory lead us to believe such products may arise from these phenomena. In particular, the possibility that many of these products result from an “unsymmetrical bifurcating surface” in the potential energy landscape is intriguing. To investigate this possibility, the Sommelet-Hauser rearrangement of N-allyl-N,N-dimethylglycine methyl ester was explored. The combined use of experimental and theoretically predicted kinetic isotope effects (KIEs) has been previously shown to deliver great mechanistic insight into reactions. The combination of these techniques, however, has found little employ in studying [2,3] rearrangements. This combination was used to study this reaction, using the Singleton method for determining small heavy-atom isotope effects. Resulting experimental KIEs suggest the reaction proceeds by an asynchronous, concerted, early transition state, and is relatively exothermic. This agrees with previous studies and Hammond’s postulate. Predicted theoretical KIEs are in good agreement with experimental KIEs, and the associated transition structure confirms the results suggested by experiment. Interestingly, as calculations proceed from gas phase to solvent models, the activation barrier of the reaction increases, while its exothermicity decreases. The energy difference determined between the lowest and second lowest energy transition structures decreases to 0.81 kcal/mol in the PCM model, so we cannot exclude the contribution of this transition structure to the reaction. However, qualitative results from the associated KIEs and energetics are consistent with the lowest energy transition structure. This reaction does not seem to afford the [1,2] product, and most likely dynamic effects are insignificant in determining product distribution. However, the study has validated, with respect to this body of reactions, both the use of the Singleton method for KIE determination and the combination of these experimental and theoretical techniques.

A primeira parte deste trabalho relata o estudo conformacional e das interações eletrônicas das α-dietoxifosforilacetofenonas-para-substituídas Y-Φ-C(O)CH2P(O)(OEt)2 (I), sendo Y= MeO, Me, H, Cl, Br, CN e NO2. Este estudo foi realizado através das espectroscopias no infravermelho, Ressonância Magnética Nuclear de 13C e 31P, apoiados por cálculos ab-initio 6-31G**. A existência de uma única banda simétrica da carbonila, tanto na transição fundamental como no 1° harmônico, conjuntamente com a constatação da ocorrência de uma única conformação de baixa energia através dos cálculos ab-initio, sugerem fortemente a existência na série estudada de um único confôrmero gauche. Os deslocamentos de frequência da carbonila do confôrmero gauche da série (I) mostraram-se negativos e aumentam significativamente em valor absoluto indo-se em para de grupos doadores a aceptores de elétrons. Contrariamente, a frequência de estiramento do grupo fosforila vPO diminui progressivamente no mesmo sentido. Este comportamento foi atribuído à ocorrência simultânea no confôrmero gauche da série (I) tanto da interação eletrostática como da transferência de carga entre o oxigênio do grupo fosforila (carregado negativamente) e o carbono carbonílico (carregado positivamente). Os estudos de Ressonância Magnética Nuclear de 13C mostraram uma constância nos deslocamentos químicos do carbono carbonílico na série (I), bem como uma expressiva blindagem do carbono carbonílico desses compostos em relação às acetofenonas correspondentes de referência. Já os deslocamentos químicos de 31P mostraram-se praticamente constantes ao longo da série estudada. Os dados de Ressonância Magnética Nuclear de 13C foram interpretados como sendo devido à ação simultânea tanto do efeito I do grupo dietoxifosforila como da transferência de carga do oxigênio do grupo fosforila ao carbono carbonílico que se encontram na relação espacial γ gauche. Os espectros no ultravioleta dos compostos da série (I) apresentam uma quase invariabilidade da energia da transição no → π* CO em relação às acetofenonas de referência correspondentes, com exceção dos compostos contendo em para substituintes fortemente atraentes de elétrons, onde ocorre uma discreta hipsocromia da transição no → π* CO. Este comportamento foi interpretado como sendo decorrente tanto da interação hiperconjugativa entre os orbitais π* CO e σ* C-P como também da interação de transferência de carga nO(PO) → π* CO, que é mais pronunciada quando o grupo fenacila dos compostos (I) contém grupos fortemente atraente de elétrons na posição para. A segunda parte da presente Dissertação relata o estudo das reações das α-halogenoacetofenonas-para-substituídas Y-Φ-C(O)CH2Hal com trietilfosfito em benzeno anidro à temperatura de refluxo de benzeno. Nessas condições observou-se a formação das α-dietoxifosforilacetofenonas-para-substituídas Y-Φ-C(O)CH2P(O)(OEt)2 (I) e dos enolfosfatos correspondentes CH2=C[Φ-Y][P(O)(OEt)2] (II), havendo mudança na proporção dos isômeros obtidos à medida que se varia tanto o substituinte na posição para do anel benzênico como a natureza do halogênio na posição α. O substituintes doadores de elétrons levam a formação preferencial dos cetofosfonatos (reação de Michael-Arbuzov) enquanto que substituintes aceptores de elétrons levam a formação preferencial de enolfosfatos (produto da reação de Perkow). Estes dados sugerem que a adição nucleofílica à carbonila com a formação dos enolfosfatos depende da afinidade eletrônica do orbital π* CO que estabiliza em maior ou menor extensão o estado de transição (III) que é o provável passo determinante da reação de Perkow. Assim sendo, no caso do para-nitro derivado que contém o LUMO (principalmente π* CO) de mais baixa energia ocorre a formação preferencial de enolfosfato, enquanto que o para-metoxi derivado onde o LUMO é desestabilizado ocorre formação preferencial do cetofosfonato. As proporções isoméricas de cetofosfonato e enolfosfato obtidos encontram-se linearmente correlacionadas com o σP de Hammet. O presente estudo evidenciou o efeito da natureza do grupo de partida (halogênio α à carbonila) na formação de enolfosfatos e cetofosfonatos nas reações estudadas, i.e constatou-se que quanto melhor for o grupo de partida para um mesmo substituinte na posição i>para das α-haloacetofenonas, maior é a proporção de enolfosfato formado em detrimento do cetofosfonato. O conjunto de dados acima descritos está de pleno acordo com a proposta mecanística de que o estado de transição (III) é o passo determinante da formação dos enolfosfatos na reação de α-haloacetofenonas-para-substituídas com trietilfosfito e praticamente exclui a possibilidade de outras propostas mecanísticas descritas na literatura. / The first part of this work reports the conformational and electronic interaction studies of some α-diethoxyphosphoryl-para-substituted acetophenones Y-Φ-C(O)CH2P(O)(OEt)2 (I), where Y= MeO, Me, H, Cl, Br, CN and NO2. This study was performed by means of infrared, 13C and 31P Nuclear Magnetic Resonance spectroscopies supported by 6-31G** ab-initio computations. The single symmetrical IR carbonyl band observed both in the fundamental and in the first overtone regions along with the existence of a unique low energy conformation obtained by ab-initio calculations, strongly suggest that a single gauche conformer should be present in the whole series (I). The carbonyl frequency shifts for the gauche rotamers of the title compounds are negative and their absolute values increase progressively on going in para position from electron-donating to electron-accepting substituents. Contrarily, the phosphoryl stretching frequencies (vPO) decrease progressively in the same direction. These trends have been ascribed to the simultaneous occurrence of the attractive electrostatic and charge transfer interactions, which take place between the negatively charged phosphoryl oxygen and the positively charged carbonyl carbon atoms in the gauche rotamer of the title compounds. The 13C NMR data showed that the carbonyl carbono chemical shifts are practically constant along the whole series (I) and that these values are significantly upfield shifted with respect to those of the corresponding parent acetophenones. This behavior has been attributed to the simultaneous occurrence of the I effect of the α-diethoxyphosphoryl group along with the charge transfer which occur between the P=O and the C=O groups which are in the γ-gauche geometry. Furthemore, the 31P chemical shifts are almost constant along the series (I). The ultraviolet spectra of the α-diethoxyphosphorylacetophenones (I) present almost the same π* CO transition energies with respect to the same transition in the corresponding acetophenones, excepting the case of the title compounds which bear at the para position strong electron-attracting groups (nitro and cyano) for which a discrete hypsochromic effect of the π* CO transition has been observed. This behavior was ascribed on the grounds of the simultaneous occurrence of the hyperconjugative interaction (IIa) and their corresponding mono- (IIb) and di- (IIc) oxygenated derivatives Y-PhC(O)CH[SOnMe][P(O)(OEt2)] [II, n=0 (a), n=1 (b)] and n=2 (c)]; c) α-bromo, α- ethylsulfonyl-para-substituted acetophenones Y-PhC(O)[Br][SO2Et] III. This study was performed by means of Infrared, Nuclear Magnetic Resonance, Ultraviolet spectroscopies, ab initio computations and X-ray diffraction analysis. For the α-ethylsulfinylacetophenones (Ia) the cis conformer predominates over the gauche one while in the case of the α-ethylsulfonylacetophenones (Ib) the gauche conformer is the more stable relative to the quasi-cis one. The α-methylthio-α-diethoxyphosphoryl acetophenones (IIa) present only a single stable conformer which bears the (SMe) group in a syn-clinal (gauche) geometry and the [P(O)(OEt2)] group in the quasi-periplanar (quasi-cis) geometry with respect to the carbonyl group. The α-methylsulfinyl-α-diethoxyphosphoryl acetophenones (IIb) display two stable conformations corresponding each one to a different diastereomer. The most stable conformer CSSS presents the methylsulfinyl group [MeS(O)] in a quasi-periplanar (quasi-cis) geometry and the diethoxyphosphoryl group [P(O)(OEt2)] in a anti-clinal (gauche) geometry relative to the carbonyl group. The second less stable conformer corresponds to the CRSS diastereomer and displays both the [MeS(O)] and the [P(O)(OEt2)] groups in a syn-clinal (gauche) geometry. The α-methylsulfonyl-α-diethoxyphosphoryl acetophenones (IIc) presents only a single stable conformer bearing both the [MeSO2] and [P(O)(OEt)2] groups in a sin-clinal geometry with respect to the carbonyl group. The α-bromo-α-ethylsulfonylacetophenones III present a single stable conformation bearing the the [SO2Et] group in a syn-periplanar (quasi-cis) geometry and the [Br] atom in a syn-clinal (gauche) geometry relative to the carbonyl group.

A presente Dissertação relata a síntese e o estudo conformacional das α-fenilseleno-α-dietóxifosforilacetofenonas para-substituídas p-X-Φ-C(O)CH[SeΦ][P(O)(OEt2] (X=OMe 1, Me 2, H 3, F 4, Cl 5, Br 6 e NO2 7) através da banda de estiramento da carbonila no infravermelho, em solventes de polaridade crescente apoiado por cálculos ab initio HF/6-3IG**. A comparação entre a freqüência e a intensidade relativa dos componentes do dubleto, para os derivados 6 e 7, e do singleto para os derivados 1-5, no solvente apolar tetracloreto de carbono, e dos componentes do dubleto, nos solventes de polaridade crescente (clorofórmio, diclorometano e acetonitrila), para os derivados 1-7, com os dados do cálculo ab initio de 3 (composto de referência), indicou que ambas as conformações estáveis (g1 e g2) apresentam a ligação C-Se na geometria anti-clinal (gauche) em relação à carbonila (C=O), enquanto que a ligação C-P assume uma geometria sin-periplanar (cis) em relação à carbonila. A análise dos contatos interatômicos de átomos relevante em comparação com a soma de seus raios de van der Waals, indicou que ambas as conformações g1 e g2 são fortemente estabilizadas pelo sinergismo das interações orbitalares e eletrostáticas π*(CO) / nSe e Oδ-[CO].....Pδ+[PO]. Analogamente, as interações mais fracas Oδ-[OR]..... Cδ+[CO], 0-Hδ+[SeΦ]....Oδ-[PO] e 0-Hδ+[ΦC(O)]....Oδ-[CO] estabilizam as conformações g1 e g2, aproximadamente na mesma extensão. No entanto, somente a conformação g1 é estabilizada pela interação eletrostática (ligação de hidrogênio) Hδ+[α-CH].....Oδ-[OR], enquanto que sómente a conformação g2 é desestabilizada pelo Efeito de Campo Repulsivo entre os dipolos Cδ+=.Oδ- e Pδ+-ORδ- Assim sendo, pode-se concluir que no dubleto de VCO no IV, o componente de maior freqüência e de menor intensidade corresponde à conformação menos estável g2 (do cálculo) enquanto que o componente de menor freqüência e mais intenso corresponde à conformação mais estável g1 (do cálculo). Estes dados estão de pleno acordo com os deslocamentos de freqüência mais negativos da carbonila (ΔVCO) do confôrmero mais estável g1 em relação ao menos estável g2. / This thesis reports the synthesis and the conformational study of some para-substituted α-phenylseleno-α-diethoxyphosphoryl-acetophenones p-X-Φ-C(O)CH[SeΦ][P(O)(OEt)2] (X=OMe 1, Me 2, H 3, F 4, Cl 5, Br 6 e NO2 7) through the analysis of the carbonyl stretching IR band, in solvents of increasing polarity, supported by ab initio HF/631G** computations of 3 (parent compound). The comparison between the frequency and the relative intensity of the doublet components for derivatives 6 and 7, and of the singlet for derivatives 1-5, in non polar solvent, carbon tetrachloride, and of the doublet components, in solvents of increasing polarity (chloroform, dichloromethane and acetonitrile), for derivatives 1-7, with the ab initio data for 3, has indicated that both stable conformations (g1 and g2 ) display the C-Se bond in an anti-clynal (gauche) geometry with respect to the carbonyl (C=O) bond, while the C-P bond assumes a syn-periplanar (cis) geometry relative to the carbonyl group. The analysis of the interatomic contacts between some relevant atoms in comparison with the sum of their van der Waals radii has shown that both g1 and g2 conformations are strongly stabilized almost to the same extension by the synergism of the π*(CO) / nSe and Oδ-[CO] .....Pδ+[PO] orbital and electrostatic interactions. Similarly, the weaker Oδ-[OR] ..... Cδ+[CO], o-Hδ+[SeΦ] ....Oδ-[PO] and o-Hδ+[ΦC(O)] ....Oδ-[CO] interactions stabilise the referred conformations almost to the same extent. However, conformer g1 only is stabilised by the electrostatic interaction (hydrogen bond) ) Hδ+[α-CH] ....Oδ-[OR], while the conformer g2 is the only one which is significantly destabilised through the Repulsive Field Effect which takes place between the Cδ+=Oδ- and Pδ+-ORδ- dipoles. Therefore it may be concluded that the less intense higher vco frequency doublet component should correspond to the less stable g2 conformation, while the more intense lower VCO frequency doublet component should be related to the more stable g1 conformation. Further support for these trends are given by the larger negative carbonyl frequency shifts (ΔVCO) for the g1 conformer relative to the g2 one, for the whole series.

Les complexes de métaux de transition, et plus particulièrement de ruthéniumII, ont connu un essor formidable depuis le milieu des années 1950 avec la découverte du complexe [Ru(bpy)3]2+. Depuis lors, de nombreuses recherches et découvertes ont permis de mettre au point un schéma photophysique prototypique pour les complexes de ruthéniumII comportant des ligands polypyridiniques. En variant la nature des ligands complexés à ce centre métallique, il a été possible de faire varier les propriétés photophysiques, photochimiques et électrochimiques des complexes résultants. Toutes ces modifications ont permis de mettre au point des complexes de ruthéniumII qui possèdent des applications dans des domaines variés. Ils sont par exemple utilisés dans le domaine de la photo-conversion d’énergie solaire ou dans le domaine de la photo-catalyse, permettant notamment de scinder l’eau en oxygène, ou de produire du dihydrogène au départ de protons. Ces complexes de ruthéniumII sont également utilisés dans le domaine biologique où ils peuvent interagir avec l’ADN via de nombreux processus. Les recherches au laboratoire de chimie organique et photochimie de l’Université libre de Bruxelles ont été concentrées sur le développement de ligands polyazaaromatiques qui possèdent un caractère π-accepteur prononcé. L’utilisation de tels ligands permet d’accéder à des complexes de ruthéniumII dont le caractère photo-oxydant est davantage prononcé que celui de leurs analogues de type [Ru(bpy)3]2+. Ce caractère photo-oxydant permet, dans le cadre d’applications biologique, d’induire la formation d’un photo-adduit résultant d’un transfert d’électron entre la guanine, base la plus réductrice de l’ADN, et le complexe de ruthéniumII. <p>Les ligands π-accepteurs permettent également de diriger et de localiser le transfert d’électron à l’état excité. Lorsque le complexe absorbe un rayonnement lumineux de bonne énergie, un électron peut être transféré du centre de ruthéniumII vers un des ligands ancillaires. Ce transfert d’électron aura lieu vers le ligand qui est le plus avide en électrons. Ce phénomène trouve des applications directes en photo-conversion d’énergie solaire. En effet, afin de convertir de l’énergie solaire, il est important d’absorber le rayonnement lumineux, mais également de pouvoir transférer cette énergie en un lieu donné. L’utilisation de ligands avides en électrons permet donc de diriger cette énergie en un lieu précis. <p>Dans le cadre de cette thèse de doctorat, nous nous sommes focalisés sur la synthèse de nouveaux ligands polyazaaromatiques qui devraient conférer des propriétés inédites aux complexes résultants. La première partie de cette thèse de doctorat a donc consisté à synthétiser des ligands polyazaaromatiques possédant un plan aromatique étendu. Nous avons mis au point une voie de synthèse pour obtenir des ligands tels que la 1,4,5,8-tétraazaphénanthrène-9,10-dione, précurseur du ligand 1,4,5,8-tétraazaphénanthrèno[9,10-b]1,4,5,8,9,12-hexaazatriphénylène (TAPHAT). Au cours de la synthèse de la 1,4,5,8-tétraazaphénanthrène-9,10-dione, nous avons également pu mettre au point une nouvelle méthode d’oxydation de noyaux de type quinoxaline à l’aide de dérivé d’iode hypervalent. Une fois la synthèse du ligand TAPHAT et des différents précurseurs effectuée, nous avons pu procéder à la synthèse des complexes de ruthéniumII. Le ligand TAPHAT, étant fortement insoluble et possédant quatre sites de chélation, nous avons décidé de procéder à la synthèse de complexes précurseurs pour préparer des complexes porteurs de ce ligand. Nous avons dès lors tenté d’obtenir les complexes précurseurs [Ru(TAP)2(diNH2TAP)]2+ et [Ru(TAP)2(tapdione)]2+. La synthèse de ces précurseurs a présenté de nombreux problèmes de chélation, donnant lieu cependant à des complexes très intéressants. Face à ces problèmes, nous nous sommes donc uniquement focalisés sur la synthèse du [Ru(TAP)2(diNH2TAP)]2+. Ce complexe précurseur a ensuite permis d’accéder à des complexes tels que le [Ru(TAP)2(HATPHE)]2+. Les complexes à base du ligand 9,10-diamino-1,4,5,8-tétraazaphénanthrène, à savoir le [Ru(TAP)2(diNH2TAP)]2+ et le [Ru(phen)2(diNH2TAP)]2+ ont ensuite été utilisés pour accéder aux complexes mono- et binucléaires symétriques du TAPHAT. Nous avons ensuite étudié les complexes à base du ligand PHEHAT ainsi que ceux à base du ligand TAPHAT et comparé leurs propriétés photophysiques, photochimiques et électrochimiques. <p>En plus de ces complexes à base de ligands PHEHAT et TAPHAT, nous avons également eu l’occasion de synthétiser des ligands analogues au ligand DPPZ. Nous avons synthétisé deux ligands plus étendus que le DPPZ, à savoir le DPQQX, dont la synthèse avait déjà été rapportée dans la littérature, et le PDPPZ. Bien que les complexes à base du ligand PDPPZ n’aient pas pu être purifiés au cours de cette thèse, nous avons tout de même pu obtenir les complexes [Ru(TAP)2(DPQQX)]2+ et [Ru(phen)2(DPQQX)]2+. Les études photophysiques, photochimique et électrochimiques ont permis de mettre en évidence de nombreuses propriétés intéressantes. De plus, des études poussées en résonance magnétique nucléaire 1H ainsi qu’en dichroïsme circulaire ont permis de montrer un processus d’auto-assemblage en solution. <p>Finalement, en plus de la synthèse de ligands polyazaaromatiques et de leurs complexes de ruthéniumII, nous avons également exploité la technique d’absorption transitoire dans le cadre d’une collaboration avec le laboratoire de résonance magnétique nucléaire. Cet axe de recherche s’est articulé autour de l’utilisation de deux complexes de ruthéniumII à savoir le [Ru(TAP)3]2+ et le [Ru(TAP)2(HAT)]2+. Ces complexes sont capables, sous illumination, de réaliser un transfert d’électron avec un réducteur. Ces processus de transfert d’électron photo-induit entre des réducteurs tels que la GMP, la N-acétyl-tyrosine, l’hydroquinone et les deux complexes de ruthéniumII ont été étudiés par les membres du laboratoire de résonance magnétique nucléaire à l’aide d’une technique dite Photo-Chemically Induced Dynamic Nuclear Polarization (Photo-CIDNP). Notre contribution a été d’investiguer les paramètres de quenching entre ces complexes et les différents réducteurs à l’aide de techniques classiques telles que la détermination de constantes de quenching via des analyses de type Stern-Volmer ainsi qu’à l’aide de techniques plus pointues telles que la photolyse éclair laser. <p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Mass spectrometry of negative ions is a convenient method for generating, isolating, and analyzing reactive intermediates that would otherwise be too short lived to detect. This ion approach is especially useful for studying the chemical properties of radicals. In this work, a negative charge-carrying group was attached to lignin model compounds and combined with collision-induced dissociation (CID) to generate and characterize radical species involved in the primary pyrolysis of lignin. The charge-tag served to increase the sensitivity of the model compounds using electrospray ionization mass spectrometry (ESI-MS) and promoted charge-remote fragmentations (CRF) upon being collisionally activated. The resulting product ions were comparable to the primary pyrolysis products of lignin; thus, CID-CRF proved to be an effective way of identifying the mechanisms by which lignin decomposes in the gas phase. <br><div><br></div><div>Additionally, this dissertation includes a review of nitrene anions. Nitrene anions are another class of reactive intermediates protected by an electron that provide a means for studying the corresponding neutral molecules via electron photodetachment spectroscopy and photoelectron spectroscopy. The added electron makes it possible for protected nitrene anions to be manipulated by external electric and magnetic fields of a mass spectrometer. Nitrene anions also display their own unique reactivities as reagents, which have been investigated using ion/molecule reactions. Mass spectrometry of negative ions has thereby provided information on the electronic states, reactivities, and thermochemical properties of nitrene intermediates.</div>

Positively charged aromatic carbon-centered σ-type mono-and biradicals have been studied previously in the gas phase. However, very little is known about the properties of related polyradicals. In this dissertation, the reactions of series of quinolinium-and acridinium-based bi-, tri-, and tetraradicals were studied with cyclohexane and allyl iodide in the gas phase by using tandem mass spectrometry. I atom abstraction and allyl group abstraction were observed as dominant reactions for all the studied radicals upon reactions with allyl iodide. Sequential H atom abstractions were observed as the major reactions for the studied bi-and tetraradicals upon reactions with cyclohexane. Surprisingly, triradicals appeared to undergo addition followed by elimination of a H atom as one of the major reactions upon interactions with cyclohexane. Vertical electron affinity and spin-spin coupling between radical sites were found to control the radical reactivities.<div><br></div><div>The radical site(s) which react first with cyclohexane were experimentally determined. For the studied biradicals, the first reacting radical sites were found to be the ones that are predicted to be more reactive based on the reactivities of related monoradicals. For the studied triradicals, the first reacting radical sites are the ones that are least strongly coupled to the other radical sites. For tetraradicals, the first two sites reacting with cyclohexane are more weakly coupled than the other two radical sites.<br></div><div><br></div><div>The mechanisms for the reactions of the triradicals with cyclohexane were proposed based on tandem mass spectrometry experiments and supported by quantum chemical calculations. Briefly, the least strongly coupled radical site of a triradical reacts with cyclohexane first by abstracting a H atom. The more reactive radical site insome of the produced biradicals will then abstract a H atom from the cyclohexyl radical within the product collision complex to generate a monoradical and cyclohexene. Some of these monoradicals undergo addition to cyclohexene within this product complex,followed by elimination of a H atom. When allowed to react with allyl iodide, all of the monoradicals and most of the biradicals demonstrated predominant I atom abstraction. The quinolinium-based meta-and para-benzynes exhibited allyl group abstraction as the major reaction. The triradicals with a meta-benzyne moiety in the pyridinium ring demonstrated dominant allyl group abstraction, which is likely to occur at the pyridinium moiety. The reaction efficienciesof these triradicals toward allyl iodide are correlated with their calculated vertical electron affinities. The other triradicals showed I atom abstraction as the major reaction. These triradicals react with allyl iodide through different mechanisms compared to those mainly abstract an allyl group. Therefore, their reactivities are not directly related to their calculated vertical electron affinities.<br></div><div><br></div><div>In the tetraradicals, spin-spin coupling between all the radical sites affects their reactivities. The coupling of the radicals in a benzyne moiety is weakened by the couplings of radical sites between two benzyne moieties. This interaction results in higher reaction efficiencies for the tetraradicals than the related benzynes. Particularly, the 2,4,7,8-tetradehydroquinolinium cation was found to have much higher reactivity than the related meta-benzyne, the 2,4-didehydroquinolinium cation. This was rationalized based on the low distortion energy of the meta-benzyne moiety in the tetraradical.<br></div><div><br></div><div>Spin-spin coupling between the radical sites in bi-, tri-, and tetraradicals significantly affect their reactivity. To better understand the relation between the effects of spin-spin coupling and the spatial distance between two radical sites, a series of acridinium-based mono-and biradicals were studied in the gas phase. The acridinium-based monoradicals are less reactive than the related quinolinium-based monoradicals, which is possibly because of the steric hindrance of the additional benzene ring. Unlike quinolinium-based biradicals, which are less reactive than the related monoradicals, acridinium-based biradicals showed higher reactivities than the monoradicals with similar vertical electron affinities. In order to better illustrate the coupling strength in the studied biradicals, the natural logarithm of their total reaction efficiencies toward cyclohexane was plotted as a function of their calculated vertical electron affinities. The plots indicate that the coupling of quinolinium-based biradicals hinders the radical reactivity, while for acridinium-based biradicals, the coupling is negligibly weak and the biradicals react as two individual monoradicals.<br></div>

This thesis describes our physical organic and mechanistic investigations into N Heterocyclic Carbene (NHC) mediated organocatalytic transformations, through a collaboration with the research group of Dr AnnMarie O'Donoghue and PhD student Richard Massey at Durham University. Initial research focused upon the determination of kinetic acidities and associated pKₐ values for a range of triazolium salts using C(3) H/D exchange, monitored by ¹H NMR spectroscopy. Estimates for pKₐ values in the range 16.6 17.4 were obtained, which are some ~2 and ~3 5 pK units lower than analogous imidazolium and thiazolium species respectively, with modest N substituent (0.3 pK units) effects observed. At lower pD values, an altered pD dependence indicates a dicationic triazolium species is formed (through N(1) protonation) with an estimated pKₐᴺ¹ of -0.2-0.5 and C(3) H pKₐ values at least 2 units lower than their monocationic analogues. This methodology was subsequently extended to mesoionic NHCs, where pKa values of 23.0 27.1 for a range of triazolium and 30.2 31.0 for a range of imidazolium salts were estimated. A detailed study of the NHC catalysed intramolecular Stetter reaction was also undertaken using ¹H NMR spectroscopy. A range of 3 (hydroxybenzyl)azolium salts (adducts), formed from the addition of NHC to aldehyde were isolated, enabling the generation of reaction profiles and the determination of rate constants. The reaction proceeds via rapid and reversible adduct generation, followed by rate limiting Breslow intermediate formation, with electron withdrawing N aryl substituents increasing the rate of product formation. Consistent with rate limiting deprotonation, deuterium exchange studies of O methylated adduct analogues found electron withdrawing N-aryl units gave faster exchange. Examination of the equilibrium constants for adduct formation revealed that both in the case of NHCs bearing 2,6 disubstituted N aryl units and aldehydes bearing a 2 ether substituent, the equilibrium position is significantly shifted towards adduct. Finally, studies at sub-stoichiometric NHC concentrations, monitored by HPLC, imply the reaction is first order with respect to NHC precursor, but zero order in aldehyde, again indicative of rate limiting deprotonation.

<p> Mass spectrometry (MS) has become one of the most powerful and versatile tools for chemical analysis due to its ultra-high sensitivity, high throughput, ease of automation, and the large amount of information obtained. Nowadays, MS is extensively used in many tasks, such as identification and quantitation of drug metabolites, analysis of the products of biomass pyrolysis, and study of reactive intermediates, to name a few. However, these mass spectrometric analyses are not without challenges. For example, the requirement for quantifying trace amounts of substances in a complex mixture constantly pushes the detection limit of mass spectrometers, and the increased sample complexity demands higher and higher mass resolution. Therefore, MS is constantly evolving to address more difficult analytical challenges. A variety of MS techniques have been developed over the years, including soft ionization methods that facilitate mass spectrometric analysis of macromolecules, such as proteins and antibodies that enables the development of new therapeutic agents, benchtop high-resolution mass spectrometers, such as the orbitraps that can be used to analyze some of the most complex mixtures, and portable mass spectrometers which can be used in the home and garden and even in cancer surgery. Besides its applications in chemical analysis, MS can serve as a unique tool for the fundamental study of gas-phase ion/molecule reactions, these gas-phase reactions can be used to better understand the reactivities of many reactive intermediates and to obtain structural information for unknown analytes.</p><p></p><p> This thesis is aimed at addressing challenges involved in mass spectrometric analyses of isomeric drug metabolites (Chapter 4), quantitation of drug metabolites by using tandem mass spectrometry coupled with liquid chromatography (LC-MS/MS) (Chapter 5), delineating cellulose depolymerization mechanisms upon fast pyrolysis by using pyrolysis-tandem mass spectrometry (py-MS/MS) (Chapter 6), and studying the reactivities of vinyl cation intermediates (Chapter 7). An overview of the dissertation research is given in Chapter 1, the instrumentation and principles of linear quadrupole ion trap (LQIT) mass spectrometer are discussed in Chapter 2, and the organic synthesis performed for several studies is detailed in Chapter 3.</p>

O sistema peroxioxalato possui diversas aplicações analíticas, principalmente devido aos altos rendimentos de emissão obtidos e relativa simplicidade. Aqui se estudou a alta eficiência desse sistema em diversas frentes, comparando-o a sistemas semelhantes, relacionando-o com um sistema intramolecular eficiente, procurando a estrutura do seu intermediário de alta energia e investigando as etapas de produção desse, tentando-se obter informações experimentais e teóricas sobre essa reação. A cinética do sistema peroxioxalato foi estudada utilizando-se como ativador o naftaleno, um composto aromático relativamente simples, que permite a aplicação de cálculos teóricos precisos ao sistema. Esses estudos teóricos dos complexos de transferência de carga entre naftaleno e o 1,2-dioxetano, a 1,2-dioxetanona e a 1,2-dioxetanodiona mostraram que a acessibilidade dos estados excitados está diretamente relacionada às propriedades eletrônicas do peróxido envolvido. Estudando-se os ânions radicais desses peróxidos se observou que o aumento no número de carbonilas do peróxido faz dele um melhor aceptor de elétron e que, especificamente para a 1,2-dioxetanona, a transferência de elétron é capaz de promover um caminho de decomposição sem barreiras energéticas. Estudos cinéticos da reação peroxioxalato utilizando DBU como catalisador básico forte não nucleofílico indicaram a viabilidade da reação nessas condições, embora com velocidades altas. Entretanto, não foi possível obter resultados cinéticos usando fenolatos como ativadores. Experimentos de adição retardada de ativador também foram efetuados usando um solvente que poderia facilitar a detecção do intermediário de alta energia, observando-se um acúmulo desse intermediário nas cinéticas de emissão. Porém, não foi possível detectar esse intermediário por espectrometria de massas. Por último, verificou-se que as etapas iniciais do sistema são exotérmicas, exceto a formação do anel de quatro membros. Estudando-se esse passo detalhadamente obteve-se para uma das etapas um valor de &#961; de Hammett semelhante ao observado experimentalmente, indicativo de que essa deve ser a etapa determinante de velocidade e de que o intermediário de alta energia deve ser a 1,2-dioxetanodiona. / The peroxyoxalate system has several analytical applications, mainly due to its high emission yields and relative simplicity. Here this system high efficiency was studied in several fronts, comparing it with similar systems, connecting it with an intramolecular efficient system, searching for the structure of its high-energy intermediate and investigating the steps in its production, trying to obtain experimental and theoretical information about this reaction. The peroxyoxalate system kinetics was studied using naphthalene as activator, an aromatic compound relatively simple, that allows the application of accurate theoretical calculations to this system. These theoretical study of charge transfer complexes between naphthalene and 1,2-dioxetane, 1,2-dioxetanone, and 1,2- dioxetanedione have shown that the availability of excited states is directly related to the electronic properties of the involved peroxide. Studying the radical anion of these peroxides it was observed that an increase in the number of peroxide carbonyls makes it a better electron acceptor and that, specifically for 1,2-dioxetanone, the electron transfer can provide a barrierless decomposition path. Kinetic studies of the peroxyoxalate system using DBU as a nonnucleophilic strong base catalyst indicated the reaction feasibility in these conditions, despite its high rate. However, it was not possible to obtain kinetic results using phenolates as activators. Experiments of delayed addition of activator were made as well using a solvent that could facilitate the detection of the high-energy intermediate, observing accumulation of this intermediate in emission kinetics. Yet, it was not possible to detect this intermediate by mass spectroscopy. At last, it was verified that the initial steps of the system are exothermic, with exception of the four-membered ring formation. Studying this step in more detail, it was obtained for a step a Hammett &#961; value similar to the one observed experimentally, indicating that this step should be the rate limiting step and that the high-energy intermediate should be the 1,2-dioxetanedione.

O sistema peroxioxalato possui diversas aplicações analíticas, principalmente devido aos altos rendimentos de emissão obtidos e relativa simplicidade. Aqui se estudou a alta eficiência desse sistema em diversas frentes, comparando-o a sistemas semelhantes, relacionando-o com um sistema intramolecular eficiente, procurando a estrutura do seu intermediário de alta energia e investigando as etapas de produção desse, tentando-se obter informações experimentais e teóricas sobre essa reação. A cinética do sistema peroxioxalato foi estudada utilizando-se como ativador o naftaleno, um composto aromático relativamente simples, que permite a aplicação de cálculos teóricos precisos ao sistema. Esses estudos teóricos dos complexos de transferência de carga entre naftaleno e o 1,2-dioxetano, a 1,2-dioxetanona e a 1,2-dioxetanodiona mostraram que a acessibilidade dos estados excitados está diretamente relacionada às propriedades eletrônicas do peróxido envolvido. Estudando-se os ânions radicais desses peróxidos se observou que o aumento no número de carbonilas do peróxido faz dele um melhor aceptor de elétron e que, especificamente para a 1,2-dioxetanona, a transferência de elétron é capaz de promover um caminho de decomposição sem barreiras energéticas. Estudos cinéticos da reação peroxioxalato utilizando DBU como catalisador básico forte não nucleofílico indicaram a viabilidade da reação nessas condições, embora com velocidades altas. Entretanto, não foi possível obter resultados cinéticos usando fenolatos como ativadores. Experimentos de adição retardada de ativador também foram efetuados usando um solvente que poderia facilitar a detecção do intermediário de alta energia, observando-se um acúmulo desse intermediário nas cinéticas de emissão. Porém, não foi possível detectar esse intermediário por espectrometria de massas. Por último, verificou-se que as etapas iniciais do sistema são exotérmicas, exceto a formação do anel de quatro membros. Estudando-se esse passo detalhadamente obteve-se para uma das etapas um valor de &#961; de Hammett semelhante ao observado experimentalmente, indicativo de que essa deve ser a etapa determinante de velocidade e de que o intermediário de alta energia deve ser a 1,2-dioxetanodiona. / The peroxyoxalate system has several analytical applications, mainly due to its high emission yields and relative simplicity. Here this system high efficiency was studied in several fronts, comparing it with similar systems, connecting it with an intramolecular efficient system, searching for the structure of its high-energy intermediate and investigating the steps in its production, trying to obtain experimental and theoretical information about this reaction. The peroxyoxalate system kinetics was studied using naphthalene as activator, an aromatic compound relatively simple, that allows the application of accurate theoretical calculations to this system. These theoretical study of charge transfer complexes between naphthalene and 1,2-dioxetane, 1,2-dioxetanone, and 1,2- dioxetanedione have shown that the availability of excited states is directly related to the electronic properties of the involved peroxide. Studying the radical anion of these peroxides it was observed that an increase in the number of peroxide carbonyls makes it a better electron acceptor and that, specifically for 1,2-dioxetanone, the electron transfer can provide a barrierless decomposition path. Kinetic studies of the peroxyoxalate system using DBU as a nonnucleophilic strong base catalyst indicated the reaction feasibility in these conditions, despite its high rate. However, it was not possible to obtain kinetic results using phenolates as activators. Experiments of delayed addition of activator were made as well using a solvent that could facilitate the detection of the high-energy intermediate, observing accumulation of this intermediate in emission kinetics. Yet, it was not possible to detect this intermediate by mass spectroscopy. At last, it was verified that the initial steps of the system are exothermic, with exception of the four-membered ring formation. Studying this step in more detail, it was obtained for a step a Hammett &#961; value similar to the one observed experimentally, indicating that this step should be the rate limiting step and that the high-energy intermediate should be the 1,2-dioxetanedione.