Thermolysis of CoRu(CO)7(m -PPh2) (1) in refluxing 1,2-dichloroethane in the presence of the diphosphine ligands 2,3-bis(diphenylphosphino)maleic anhydride (bma) and 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) furnishes the new mixed-metal complexes CoRu(CO)4(μ -P-P)(μ -PPh2) [where P-P = bma (3); bpcd (6)], along with trace amounts of the known complex CoRu(CO)6(PPh3)(μ -PPh2) (4). The requisite pentacarbonyl intermediates CoRu(CO)5(μ -P-P)(μ -PPh2) [where P-P = bma (2); bpcd (5)] have been prepared by separate routes and studied for their conversion to CoRu(CO)4(μ -P-P)(μ -PPh2). The complexes 2/3 and 5/6 have been isolated and fully characterized in solution by IR and NMR spectroscopy. The kinetics for the conversion of 2→3 and of 5→6 were measured by IR spectroscopy in chlorobenzene solvent. On the basis of the first-order rate constants, CO inhibition, and the activation parameters, a mechanism involving dissociative CO loss as the rate-limiting step is proposed. The solid-state structure of CoRu(CO)4(μ -bma)(μ -PPh2) (3) reveals that the two PPh2 groups are bound to the ruthenium center while the maleic anhydride π bond is coordinated to the cobalt atom. Thermolysis of the cluster Ru3(CO)12 with the bis(phosphine)hydrazine ligand (MeO)2PN(Me)N(Me)P(OMe)2 (dmpdmh) in toluene at 75°C furnishes the known clusters Ru4(CO)12[μ -N(Me)N(Me)] (9) and Ru3(CO)11[P(OMe)3] (10), in addition to the new cluster Ru3(CO)10(dmpdmh) (8) and the phosphite-tethered cluster Ru3(CO)9[μ -P(OMe)3] (11). The simple substitution product Ru3(CO)10(dmpdmh), a logical intermediate to clusters 9-11, was synthesized by treating Ru3(CO)12 and dmpdmh with Me3NO in CH2Cl2 at room temperature, and independent thermolysis reactions using cluster 8 were shown to yield clusters 9-11. The tetrahedrane cluster FeCo2(CO)9(μ3-S) reacts with the redox-active ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) to give the disubstituted cluster FeCo2(CO)7(bpcd)(μ3-S) as the sole product. This diphosphine-substituted cluster contains a cobalt-bound, chelating bpcd ligand. The solid-state structure has been unequivocally established by X-ray diffraction analysis. Cyclic voltammetric studies on FeCo2(CO)7(bpcd)(μ3-S) reveal the presence of two quasireversible redox responses assigned to the 0/1- and 1-/2- redox couples. The orbital composition of these redox couples has been examined by carrying out extended Hückel MO calculations on the model complex FeCo2(CO)7(H4-bpcd)(μ3-S), with the results being compared to related cluster compounds.

<p> A series of 2-substituted Δ^3-1,3,4-oxadiazolines (i) were synthesized by oxidation of the corresponding hydrazones with lead-tetraacetate in alcohol, eq A. (See Diagram A in Thesis)</p> <p> These oxadiazolines, upon thermolysis, generated carbonyl ylide intermediates (ii). These ylides are known to undergo fragmentation into carbenes and carbonyl compounds, eq B. (See Diagram B in Thesis)</p> <p> A new series of products were found from the thermolysis of these types of oxadiazolines, ester azines iv and v. A possible mechanism for the formation of these ester azines involves carbene attack on the oxadiazoline to give an azomethine imine intermediate (iii) which can subsequently rearrange to give the azines and carbonyl compounds, eq C. (See Diagram C in Thesis)</p> <p> This mechanism is supported by the observation that the overall yields of ester azines rise with increasing initial concentration of oxadiazoline whereas the yield of propene, a rearrangement product of dimethyl carbene, falls with increasing initial concentration of oxadiazoline.</p> <p> The ester azines (R=CH3, CH2CH3 and CH(CH3)2) were found to be uniconfigurational and the E-configuration was assigned to ester azine iv and the E,E-configuration was assigned to ester azine v. Ester azines (R=C(CH3)3) were found to exist as configurational isomers. Equilibration studies were carried out on these ester azines and the thermodynamic parameters ΔG°, ΔH° and ΔS° were found for equilibration shown in eq D. (See Diagram D in Thesis)</p> <p> Changing the R' substituent of i to OCH2CCl3 or OCH2CF3 did not stop fragmentation of the derived ylide. Ester azines were found from the thermolysis of these oxadiazolines also. They were found to be uniconfigurational and were assigned the E-configuration.</p> / Thesis / Master of Science (MSc)

<p> 1,1-Diarylindenes rearrange when heated or irradiated to give 1,2- and 2,3-diarylindenes. Three 1,1-diarylindenes were synthesized and used in an attempt to probe the transition states for phenyl migration in both the ground and excited state. The three indenes synthesized were: 1-(p-bromophenyl)-1-phenylindene, 1-(p-cyanophenyl)-1-phenylindene and 1-(p-methoxyphenyl)-1-phenylindene.</p> <p> On direct irradiation, the migratory aptitudes were -C6H4CN-p, 98%; -C6H4OCH3-p, 95%; and -C6H4Br-p, 86%. On heating (258°C) the following aptitudes were found: -C6H4CN-p, 82%; -C6H4OCH3-p, 48%; and -C6H4Br-p, 53%. The products were synthesized independently, and the product ratios obtained upon reaction were measured from the n.m.r. of mixtures, and by v.p.c. A charge transfer mechanism was put forward to explain the preference for migration of the substituted group in the excited state. Such charge transfer contributions are known to increase the rates of quenching in donor-acceptor pairs. A radical-type transition state was postulated as being present in the ground state migration. The rate constant for excited state rearrangement was calculated to be 4.9 x 10^9 sec^-1 .</p> / Thesis / Doctor of Philosophy (PhD)

Objetivou-se com este estudo compreender as dinâmicas das temperaturas corporais em fêmeas da raça Nelore, e relacionar os aspectos fisiológicos da termorregulação com as respostas celulares pela expressão de proteínas de choque térmico. O projeto foi desenvolvido no Laboratório de Biometeorologia e Etologia, da Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, Pirassununga-SP. Foram utilizadas 20 vacas Nelore pluríparas, cíclicas, mantidas em sistema de pastejo. O período experimental precedeu a estação de monta de 2013 e terminou na inseminação artificial. Para classificar os animais quanto ao gerenciamento de calor foi monitorada a temperatura vaginal durante seis dias por meio de 16 data loggers (n=16). Com o intuito de melhor compreender o gerenciamento de calor, outras respostas fisiológicas, nomeadamente temperatura retal, caudal, ocular, frequência respiratória e taxa de sudação foram colhidas durante os quatro dias finais do monitoramento da temperatura vaginal. Para expressão gênica relativa colheram-se amostras de sangue (n=20). Foram realizados choques térmicos in vitro a 38ºC, 40ºC e 42ºC por duas horas. Após tratamento térmico obteve-se o pellet de leucócitos para posterior extração do RNA pelo método TRIzol. Foram escolhidas 10 vacas com os melhores resultados de concentração de RNA, 5 pertencentes ao grupo de vacas eficientes quanto ao gerenciamento de calor, e 5 não eficientes (n=10). A RT-PCR foi realizada com o kit SuperScript III. A reação polimerase em cadeia em tempo real (qPCR) ocorreu no aparelho StepOnePlus® Applied Biosystem utilizando como marcador fluorescente o SYBR® Green para os genes alvo validados HSPA1A, HSPD1, HSP90AA1, HIF1A e endógenos ACTB, RPL15 e PPIA. Os dados foram analisados por ANOVA, regressão e correlação do SAS 9.2. As vacas foram classificadas em eficientes e não eficientes por meio de coeficientes angulares, advindos da regressão das temperaturas vaginais durante períodos de ganho e perda de calor. As vacas eficientes apresentaram menores temperaturas retais 37,65ºC (P<0,01) e maior taxa de sudação 528,73 g. m-². h-¹ (P<0,06). A nível celular, o aumento programado in vitro da temperatura não aumentou quantidade de transcritos, promovendo manutenção à 38ºC e 40ºC e declínio à 42ºC. A ordem decrescente da abundância de transcritos foi HSPA1A, HSPD1 e HSP90AA1. Pode-se concluir que vacas Nelore com diferentes gerenciamentos de calor apresentam respostas termorregulatórias diferentes. A HSPA1A apresentou a maior abundância de transcritos sendo considerada como marcador molecular para termotolerância, por ser a mais sensível à temperatura e bem conservada. Não foi observado diferença nas expressões gênicas relativas das proteínas de choque térmico entre os animais classificados quanto ao gerenciamento de calor. / The aim of this study was to understand the dynamics of body temperatures in Nellore females, and relate the physiological aspects of thermoregulation with cellular responses by the expression of heat shock proteins. The project was developed in Biometeorology and Ethology Laboratory, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga-SP. Were used 20 Nellore pluriparous cows, cyclical, kept in grazing system. The experimental period preceded the 2013\' breeding season and ended up in artificial insemination. To classify animals in relation to heat management the vaginal temperature was monitored for six days through 16 data loggers (n=16). In order to better understand the heat management, other physiological responses, including rectal, tail and eye temperatures, respiratory rate and sweating rate were taken during the final four days of vaginal temperature monitoring. For gene expression was harvested blood samples (n=20). in vitro heat shocks were performed at 38ºC, 40ºC and 42ºC during two hours. After the heat treatment was obtained the leukocyte pellet for later RNA extraction by TRIzol method. Ten cows were chosen with the best RNA concentration results, five belonging to the group of cows efficient on heat management and five inefficient (n = 10). RT-PCR was performed with SuperScript III kit. The real-time polymerase chain reaction (qPCR) occurred in StepOnePlus® Applied Biosystems instrument using the SYBR® Green as fluorescent marker to the target validated genes HSPA1A, HSPD1, HSP90AA1, HIF1A and the endogenous ACTB, RPL15 and PPIA. Data were analyzed using ANOVA, regression and correlation SAS 9.2. The cows were classified as efficient and inefficient through angular coefficients, derived from regression of vaginal temperatures for the gain and heat loss periods. Efficient cows had lower rectal temperature 37.65ºC (P<0.01), higher sweating rate 528.73 g. m ². h-¹ (P<0.06). At cellular level, the increase of in vitro programmed temperature has not increased the transcripts amount, promoting the maintenance at 38ºC and 40ºC and decline at 42ºC. The decreasing order of transcripts amount was HSPA1A, HSPD1 and HSP90AA1. It can be concluded that Nellore cows with different heat managements has different thermoregulatory responses. The HSPA1A showed the highest transcripts abundance being considered as a molecular marker for thermotolerance, for being more sensitive to temperature and better conserved. There was no difference in gene expression for heat shock proteins between animals classified by heat management.

Membrane materials for gas separations span a wide range including polymers, metals, ceramics and composites. Our aim is to create economical hydrothermally stable membranes that can provide high H₂-CO₂ separation at a temperature of 300 degree Celsius, for application in the water-gas shift reactor process. The present work describes the development of novel silica and silica-titania membranes from the controlled oxidative thermolysis of polydimethylsiloxane. The scope of this thesis is fabrication of membranes, material characterization and preliminary gas permeation tests (35-80 degree Celsius) on PDMS derived silica membrane films. The developed membranes can withstand up to 350 degree C in air. High permeabilties of small gas penetrants like He, H₂ and CO₂ have been observed and fairly high separation factors of O₂/N₂=3, H₂/N₂= 14 and H₂/CH₄=11 have been obtained. As the temperature of operation increases, the permeability of hydrogen increases and the separation factor of H₂ from CO₂ increases. The silica membranes exhibit gas separation factors higher than the respective Knudsen values. Additionally, design and construction of a new high temperature gas permeation testing system is described, which will cater to gas permeation tests at temperatures up to 300 degree Celsius for future work. The thesis also includes a detailed plan for future studies on this topic of research.

Objetivou-se com este estudo compreender as dinâmicas das temperaturas corporais em fêmeas da raça Nelore, e relacionar os aspectos fisiológicos da termorregulação com as respostas celulares pela expressão de proteínas de choque térmico. O projeto foi desenvolvido no Laboratório de Biometeorologia e Etologia, da Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, Pirassununga-SP. Foram utilizadas 20 vacas Nelore pluríparas, cíclicas, mantidas em sistema de pastejo. O período experimental precedeu a estação de monta de 2013 e terminou na inseminação artificial. Para classificar os animais quanto ao gerenciamento de calor foi monitorada a temperatura vaginal durante seis dias por meio de 16 data loggers (n=16). Com o intuito de melhor compreender o gerenciamento de calor, outras respostas fisiológicas, nomeadamente temperatura retal, caudal, ocular, frequência respiratória e taxa de sudação foram colhidas durante os quatro dias finais do monitoramento da temperatura vaginal. Para expressão gênica relativa colheram-se amostras de sangue (n=20). Foram realizados choques térmicos in vitro a 38ºC, 40ºC e 42ºC por duas horas. Após tratamento térmico obteve-se o pellet de leucócitos para posterior extração do RNA pelo método TRIzol. Foram escolhidas 10 vacas com os melhores resultados de concentração de RNA, 5 pertencentes ao grupo de vacas eficientes quanto ao gerenciamento de calor, e 5 não eficientes (n=10). A RT-PCR foi realizada com o kit SuperScript III. A reação polimerase em cadeia em tempo real (qPCR) ocorreu no aparelho StepOnePlus® Applied Biosystem utilizando como marcador fluorescente o SYBR® Green para os genes alvo validados HSPA1A, HSPD1, HSP90AA1, HIF1A e endógenos ACTB, RPL15 e PPIA. Os dados foram analisados por ANOVA, regressão e correlação do SAS 9.2. As vacas foram classificadas em eficientes e não eficientes por meio de coeficientes angulares, advindos da regressão das temperaturas vaginais durante períodos de ganho e perda de calor. As vacas eficientes apresentaram menores temperaturas retais 37,65ºC (P<0,01) e maior taxa de sudação 528,73 g. m-². h-¹ (P<0,06). A nível celular, o aumento programado in vitro da temperatura não aumentou quantidade de transcritos, promovendo manutenção à 38ºC e 40ºC e declínio à 42ºC. A ordem decrescente da abundância de transcritos foi HSPA1A, HSPD1 e HSP90AA1. Pode-se concluir que vacas Nelore com diferentes gerenciamentos de calor apresentam respostas termorregulatórias diferentes. A HSPA1A apresentou a maior abundância de transcritos sendo considerada como marcador molecular para termotolerância, por ser a mais sensível à temperatura e bem conservada. Não foi observado diferença nas expressões gênicas relativas das proteínas de choque térmico entre os animais classificados quanto ao gerenciamento de calor. / The aim of this study was to understand the dynamics of body temperatures in Nellore females, and relate the physiological aspects of thermoregulation with cellular responses by the expression of heat shock proteins. The project was developed in Biometeorology and Ethology Laboratory, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga-SP. Were used 20 Nellore pluriparous cows, cyclical, kept in grazing system. The experimental period preceded the 2013\' breeding season and ended up in artificial insemination. To classify animals in relation to heat management the vaginal temperature was monitored for six days through 16 data loggers (n=16). In order to better understand the heat management, other physiological responses, including rectal, tail and eye temperatures, respiratory rate and sweating rate were taken during the final four days of vaginal temperature monitoring. For gene expression was harvested blood samples (n=20). in vitro heat shocks were performed at 38ºC, 40ºC and 42ºC during two hours. After the heat treatment was obtained the leukocyte pellet for later RNA extraction by TRIzol method. Ten cows were chosen with the best RNA concentration results, five belonging to the group of cows efficient on heat management and five inefficient (n = 10). RT-PCR was performed with SuperScript III kit. The real-time polymerase chain reaction (qPCR) occurred in StepOnePlus® Applied Biosystems instrument using the SYBR® Green as fluorescent marker to the target validated genes HSPA1A, HSPD1, HSP90AA1, HIF1A and the endogenous ACTB, RPL15 and PPIA. Data were analyzed using ANOVA, regression and correlation SAS 9.2. The cows were classified as efficient and inefficient through angular coefficients, derived from regression of vaginal temperatures for the gain and heat loss periods. Efficient cows had lower rectal temperature 37.65ºC (P<0.01), higher sweating rate 528.73 g. m ². h-¹ (P<0.06). At cellular level, the increase of in vitro programmed temperature has not increased the transcripts amount, promoting the maintenance at 38ºC and 40ºC and decline at 42ºC. The decreasing order of transcripts amount was HSPA1A, HSPD1 and HSP90AA1. It can be concluded that Nellore cows with different heat managements has different thermoregulatory responses. The HSPA1A showed the highest transcripts abundance being considered as a molecular marker for thermotolerance, for being more sensitive to temperature and better conserved. There was no difference in gene expression for heat shock proteins between animals classified by heat management.

Indiana University-Purdue University Indianapolis (IUPUI) / In the area of forensic chemistry, improved or new analysis methods are continually being investigated. One common and powerful technique used in forensic chemistry is wall-coated open-tubular column (WCOT) gas chromatography with electron ionization single quadrupole mass spectrometry (GC-MS). Improvements to and effectiveness of alternatives to this instrumental platform were explored in an array of parallel inquiries. The areas studied included the column for the chromatographic separation, the universal detection method employed, and the fragmentation method used to enhance molecular identification. Superfine-micropacked capillary (SFµPC) columns may provide an alternative to commercial packed GC columns and WCOT GC columns that combines the benefits of the larger sample capacity of packed columns and the benefits of the excellent separation capabilities and mass spectrometry (MS) flow rate compatibility of WCOT columns. SFµPC columns suffer from high inlet pressure requirements and prior reported work has required specialized instrumentation for their use. Fabrication of and chromatography with SFµPC GC columns was successfully achieved with typical GC-MS instrumentation and within the flow rate limit of a MS. Additionally, the use of higher viscosity carrier gasses was demonstrated to reduce the required inlet pressure for SFµPC GC columns. Recently, a new vacuum ultraviolet spectrometer (VUV) universal detector has been commercialized for GC. The ability of VUV detectors to acquire absorbance spectra from 125 nm to 430 nm poses a potential alternative to MS. As such, GC-VUV provides an exciting potential alternative approach to achieving excellent quantitative and qualitative analysis across a wide range of analytes. The performance of VUV and MS detectors for forensic analysis in terms of quantitative and qualitative analysis was compared. Analysis of alkylbenzenes in ignitable liquids was explored, which can be important evidence from suspected arson fires and are difficult to differentiate with MS. The VUV detector was found to have superior specificity and comparable sensitivity to the MS detector in scan mode. Addition of thermolysis (Th) as an orthogonal fragmentation pathway provides the opportunity to increase the differences between MS fragmentation patterns. Fragmentation has been widely established to aid in identification of molecules with MS by providing characteristic fragments at characteristic relative abundances. However, molecules with very similar structures do not result in sizable spectral differences in all cases with typical MS fragmentation techniques. A series of Th units were fabricated and integrated into GC-Th-MS instruments. Th-MS was conducted with the thermally labile nitrate esters across a range of instrumentation and thermal conditions.

In der vorliegenden Arbeit wird die Konzeptionierung und die Realisierung eines teilkontinuierlichen Thermolyseverfahrens zur rohstofflichen Verwertung von Polyethylen- und Polypropylenabfällen beschrieben. Die Ausführung in der zweistufigen Rührkesselkaskade gewährleistete dabei die Trennung der Prozessschritte Schmelzen sowie Cracken der Einsatzmaterialien, woraus ein Thermolyseöl hervorging, welches weitestgehend frei von den Verunreinigungen aus den Abfällen war. Das Thermolyseöl wies eine Zusammensetzung aus Benzin- und Dieselkomponenten auf und erfüllte einige entscheidende Kraftstoffkriterien. Zur Senkung der qualitätsmindernden Olefingehalte wurden in einem weiteren Teil dieser Arbeit Untersuchungen zur heterogen-katalysierten Hydrierung der Siedeschnitte im Schüttgutreaktor und im Rührautoklav durchgeführt. Dabei konnten die Olefingehalte durch den Einsatz eines Palladium-Platin-Trägerkatalysators sowie durch einen Nickel-Gerüstkatalysator maßgeblich gesenkt werden. Als unerwünschtes Nebenprodukt des Thermolyseprozesses resultierte ein geringer Anteil Koks, welcher in der Schmelze akkumulierte und sich teilweise an der Reaktorwand ablagerte. Die entstandenen Mengen wiesen eine Abhängigkeit von der Prozesstemperatur und -dauer auf und mussten aus dem Prozess geschleust werden. Als weitere Nebenprodukte traten ein leichtflüchtiges Spaltgas sowie ein Sumpfrückstand auf. Darüber hinaus wurde gezeigt, dass die aufzuwendende Energie für den Thermolyseprozess durch die Energiegehalte der Nebenprodukte gedeckt werden kann. Neben dem Einsatz als Kraftstoff empfahl sich das Thermolyseöl aufgrund seiner physikalischen und chemischen Eigenschaften gerade im Hinblick auf einen nachhaltigen Umgang mit Ressourcen als beachtenswerter Ersatz für fossiles Rohöl.

Les céramiques de type non-oxyde à base de silicium ont été très largement étudiées en raison deleurs incroyables propriétés thermostructurales généralement très supérieures à celles desmatériaux conventionnels. En particulier, les carbonitrures de bore et de silicium (SiBCN)proposent une grande fiabilité mécanique et sont stables jusqu’à des températures de l’ordre de2200 °C en raison de la faible mobilité atomique de leurs structures. Le développement de la voie« polymères précéramiques » s’est avéré primordial pour la réalisation de céramiques techniquesaux propriétés contrôlées. Au travers de la thermolyse des polymères, une large gamme decéramiques peut être obtenue à partir de précurseurs moléculaires en contrôlant à la fois lastructure de l’unité monomérique et le degré de polymérisation, mais aussi la procédure dethermolyse. La thermolyse directe des polymères est compatible avec plusieurs types detechniques de mise en forme et offre la possibilité de réaliser des structures et des objets deformes complexes. Le nanomoulage à partir d’un moule poreux et le co-assemblage d’unpolymère précéramique et d’un bloc copolymère sont deux voies largement empruntées pour laproduction de céramiques poreuses ordonnées. Ce manuscrit présente une étude sur l’élaborationde céramiques de type SiBCN mésoporeuses ordonnées selon la méthode du nanomoulage. Lamise en forme de ces poudres céramiques par frittage flash conduit alors à la fabrication demonolithes à porosité hiérarchisée. Une deuxième partie envisage également l’utilisation d’uncopolymère tribloc comme agent structurant pour la synthèse de matériaux mésoporeux ordonnésde type carbure de silicium. / SiC based non-oxide type ceramics have been largely studied due to high thermostructural properties.In particular, Silicoboron carbonitrides (SiBCN) display high mechanic reliability and stay stableuntil temperature such as 2200 °C due to a low atomic mobility in their structure. The developpementof the Polymer Derived Ceramics (PDCs) route played a major role in the production of technicalceramics with controlled properties. Through the thermolysis of preceramic polymers, a large rangeof ceramics can be obtained from molecular precursors while controlling at the same time themonomeric unit structure, the polymerization level but also the thermolysis process. Directthermolysis of polymers is compatible with many shaping techniques and offers the opportunity torealize complex shapes/structures. Nanocasting from a porous template and self-assembling of apreceramic polymer and multi-bloc copolymers are the main strategies leading to organized porousceramics. This document is about the fabrication of organized mesoporous SiBCN-type ceramics viananocasting. The shaping of such ceramic powders with the spark plasma sintering technique leads tomonoliths with hierarchical porosity. A second part considers the use of a commercial tri-blockcopolymer as structuring agent for the synthesis of SiC-type ordered materials.

Quantum chemical studies on lowcoordinated group 14-16 compounds have been performed. This thesis focuses particularly on silenes influenced by reverse Siδ-=Cδ+ bond polarization. Hypercoordinated carbon compounds are also studied. The geometries from calculations with several common computationally inexpensive methods have been tested against high level CCSD/cc-pVTZ geometries for a series of substituted silenes. Hybrid HF/DFT methods performed best among the inexpensive methods tested for silenes. Heavy alkenes strongly influenced by reverse polarization are found to have less exothermic dimerization energies for both head-to-head and head-to-tail dimerizations, and to have higher activation energies for water addition than naturally polarized heavy alkenes. We also investigated solvated lithium, magnesium and potassium silenolates and found that lithium and magnesium ions coordinate preferably to O, giving their SiC bond some double bond character. Reverse polarized 2-siloxy-, 2-thiosiloxy-, and 2-(N-sila-N-methyl)-silenes could according to calculations be formed thermolytically from the corresponding tetrasilanes as transient species. It was, however, found that silenes highly influenced by π-conjugative reverse polarization have low barriers for the back-reaction, and thus these silenes are more difficult to form as stable species than naturally polarized silenes. It is also found that conjugated 1-siladienes, formed by electrocyclic ring-opening of 1-silacyclobut-2-enes, which are highly influenced by π-conjugative reverse polarization, have higher barriers for electrocyclization back to starting material than naturally polarized 1-siladienes. It is found that CHe54+, CHe64+, CNe54+, and CNe64+ are the closest carbon analogs of SiH5-, SiH62-, SiF5- and SiF62-, respectively. However, due to their exothermic dissociation reaction, these very high-lying local minima will be impossible to reach experimentally.