Density Functional Theory (DFT) is an effective tool for studying diverse metal systems. Presented herein are studies of a variety of metal systems, which can be applied to accomplish transformations that are currently difficult/impossible to achieve. The specific topics studied utilizing DFT include: 1) C–H bond activation via an Earth-abundant transition metal complex, 2) C–H bond deprotonation via an alkali metal superbase, 3) and amination/aziridination reactions utilizing a CuI reagent. Using DFT, the transformation to methanol (CH3OH) from methane (CH4) was examined. The transition metal systems studied for this transformation included a model FeII complex. This first-row transition metal is an economical, Earth-abundant metal. The ligand set for this transformation includes a carbonyl ligand in one set of complexes as well as a phosphite ligand in another. The 3d Fe metal shows the ability to convert alkyls/aryls to their oxidized counterpart in an energetically favorable manner. Also, “superbasic” alkali metal amides were investigated to perform C—H bond cleavage. Toluene was the substrate of interest with Cs chosen to be the metal of interest because of the highly electropositive nature of this alkali metal. These highly electrophilic Cs metal systems allow for very favorable C—H bond scission with a toluene substrate. Finally, the amination and aziridination of C–H and C=C bonds, respectively, by a CuI reagent was studied. The mechanism was investigated using DFT calculations. Presently, these mechanisms involving the use of coinage metals are debated. Our DFT simulations shed some insight into how these transformations occur and ultimately how they can be manipulated.

Thermal reactions and flash photolysis are used to study the olefin bond-migration promoted by tungsten carbonyls. Substitution of piperidine (pip) by 2- allylphenyldiphenylphosphine (adpp) in the cis-(pip)(η^1- adpp)W(CO)-4 complex was investigated, and no olefin bond-migration was observed. This suggests that a vacant coordinated site adjacent to the coordinated olefin is an essential requirement for olefin bond rearrangement. The rates of olefin attack on the photogenerated coordinatively unsaturated species, cis-[(CB)(η^1-ol- P)W(CO)-4] (CB = chlorobenzene, p-ol = Ph-2P(CH-2)-3CH=CH-2; n = 1-4) were measured. Kinetics data obtained both in pure CB and in CB/cyclohexane mixtures support a dissociative mechanism in which the W-CB bond is broken in the transition state. In contrast to results observed in studies of other related systems, no olefin bond-migration is noted. This observation is attributed to P-W coordination at all stages of the reaction, which precludes formation of a reactive intermediate containing a vacant coordination site adjacent to a P-ol bond.

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Made available in DSpace on 2014-12-17T15:42:00Z (GMT). No. of bitstreams: 1 JulioCOS_DISSERT.pdf: 1559177 bytes, checksum: 5d76456c4b64130c51ab0adec9c84e15 (MD5) Previous issue date: 2010-08-16 / This research aims at identifying the learning problems in newly undergraduate students at university, interpreting the nature and causes of these problems, offering subsidies to overcome these difficulties and enabling a meaningful learning through which students give meaning to their learning. As an object for this work was chosen the theme Chemical Bonds - where were studied the forces between atoms to form molecules, compound ions and ionic crystalline structures - and is characterized as one of the most important subjects of Chemistry. In research, it was used a questionnaire with five open questions, answered by 147 students from the early periods of degrees in Chemistry at Universidade Federal do f Rio Grande do Norte. The answers revealed uncertainty on the part of students, both conceptual and representation, with superficial justifications, always using the octet rule to describe models of chemical bonds. Results suggest that these students had inadequate training in high school and that the examinations for entrance into the ranks were made according to flexible criteria less demanding in terms of knowledge. These observations have led to the conclusion that for future changes, it is necessary for high schools and in the early periods in universities favoring the adoption of pedagogical approaches in context and applying strategies to overcome the teaching of superficial memorization on Chemical Bonds, which probably have applied to the teaching of other subjects of chemistry / Este trabalho teve o objetivo de identificar problemas de aprendizagem em alunos de gradua??o rec?m ingressante na universidade, interpretar a natureza e as causas desses problemas, oferecendo subs?dios para supera??o de tais dificuldades e possibilitando uma aprendizagem significava atrav?s da qual o aluno atribua sentido em seu aprendizado. Para o desenvolvimento desse trabalho foi escolhido o tema Liga??es Qu?micas - onde se estudam as for?as que agem entre os ?tomos para formar mol?culas, ?ons compostos ou estruturas cristalinas i?nicas -, que se caracteriza como um dos mais importantes assuntos da Qu?mica. Para isso, utilizou-se um question?rio com cinco perguntas abertas, respondidas por 147 estudantes dos per?odos iniciais das gradua??es em Qu?mica da Universidade Federal do Rio Grande do Norte. As respostas obtidas revelaram inseguran?a dos estudantes, tanto em termos conceituais quanto de representa??o, com justificativas superficiais, recorrendo sempre ? regra do octeto para descrever modelos de liga??es qu?micas. Os resultados sugerem que esses estudantes tiveram uma forma??o inadequada, no ensino m?dio e que os exames para ingresso nas gradua??es se fizeram segundo crit?rios pouco exigentes em termos de conhecimentos. As observa??es feitas levam ? conclus?o de que, para mudan?as futuras, ? necess?rio que escolas de ensino m?dio e dos per?odos iniciais nas universidades privilegiem a ado??o de m?todos pedag?gicos contextualizados, aplicando estrat?gias para superar o ensino memor?stico e superficial sobre Liga??es Qu?micas, o que, provavelmente, se aplica ao ensino de outros temas da Qu?mica

Advances in computing capabilities have facilitated the application of quantum mechanical methods to increasingly larger and more complex chemical systems, including weakly interacting and biologically relevant species. One such ab initio-based composite methodology, the correlation consistent composite approach (ccCA), has been shown to be reliable for the prediction of enthalpies of formation and reaction energies of main group species in the gas phase to within 1 kcal mol-1, on average, of well-established experiment, without dependence on experimental parameterization or empirical corrections. In this collection of work, ccCA has been utilized to determine the proton affinities of deoxyribonucleosides within an ONIOM framework (ONIOM-ccCA) and to predict accurate enthalpies of formation for organophosphorus compounds. Despite the complexity of these systems, ccCA is shown to result in enthalpies of formation to within ~2 kcal mol-1 of experiment and predict reliable reaction energies for systems with little to no experimental data. New applications for the ccCA method have also been introduced, expanding the utility of ccCA to solvated systems and complexes with significant noncovalent interactions. By incorporating the SMD solvation model into the ccCA formulation, the Solv-ccCA method is able to predict the pKa values of nitrogen systems to within 0.7 pKa unit (less than 1.0 kcal mol-1), overall. A hydrogen bonding constant has also been developed for use with weakly interacting dimers and small cluster compounds, resulting in ccCA interaction energies for water clusters and dimers of the S66 set to within 1.0 kcal mol-1 of well-established theoretical values.

Indiana University-Purdue University Indianapolis (IUPUI) / Polyacetylenic natural products, compounds containing multiple carbon-carbon triple bonds, have been found in a large collection of organisms. Radiochemical tracer studies have indicated that these bioactive metabolites are synthesized from fatty acid precursors through a series of uncharacterized desaturation and acetylenation steps. To date, there are three main pathways believed to be involved in acetylenic natural product biosynthesis. However, it is apparent that the crepenynic acid pathway is the origin of a vast majority of the known plant and fungal acetylenic products. This investigation provides concrete evidence that the polyacetylenic natural products found in the fungus Fistulina hepatica and the medicinal plant species Echinacea purpurea are biosynthesized from crepenynic acid. Through heterologous expression in Yarrowia lipolytica, two acetylenases capable of producing crepenynic acid were identified from E. purpurea. Furthermore, heterologous expression of two diverged desaturases isolated from F. hepatica, uncovered a ∆12-acetylenase and the first multifunctional enzyme capable of ∆14-/∆16- desaturation and ∆14-acetylenation.

This study, the effects of computer simulations on the teaching and learning of Atomic Combinations was carried out in the Tshwane North District of Gauteng Province in South Africa. The study employed a non-randomized control-group pre-test and post-test quasi-experimental design involving two grade 11 Physical Science classes; one as an experimental (52) and the other as a control group (53). An Achievement Test consisting of 30 multiple-choice questions and a Structured Questionnaire designed for teacher and learner participants were the principal data collection tools used. The questionnaire was developed to answer research questions two and three that guided this study. The questionnaire tested how much learners and teachers were familiar with the use of computers and if there were any hindrances to computer usage. The achievement test instrument was administered as a pre-test and post-test to answer research question one. The experimental group received computer-assisted teaching and the control group was taught using traditional teaching method (lecture) on the same topics. The intervention took two and a half weeks for each of the schools involved in the study. Analyses of scores of the two groups in post-test were compared using Statistical Package for the Social Sciences (SPSS) independent t-test version 16.0. The results showed that t = 0.467, df = 103, p = 0.048 and the Sig. (2-tailed) value is 0.641. Since sig. (2-tailed) value is greater than 0.05, it can be concluded that there is no statistical significant difference between the experimental group and the control group. / Science and Technology Education / M. Sc. (Mathematics, Science & Technology Education)

This study, the effects of computer simulations on the teaching and learning of Atomic Combinations was carried out in the Tshwane North District of Gauteng Province in South Africa. The study employed a non-randomized control-group pre-test and post-test quasi-experimental design involving two grade 11 Physical Science classes; one as an experimental (52) and the other as a control group (53). An Achievement Test consisting of 30 multiple-choice questions and a Structured Questionnaire designed for teacher and learner participants were the principal data collection tools used. The questionnaire was developed to answer research questions two and three that guided this study. The questionnaire tested how much learners and teachers were familiar with the use of computers and if there were any hindrances to computer usage. The achievement test instrument was administered as a pre-test and post-test to answer research question one. The experimental group received computer-assisted teaching and the control group was taught using traditional teaching method (lecture) on the same topics. The intervention took two and a half weeks for each of the schools involved in the study. Analyses of scores of the two groups in post-test were compared using Statistical Package for the Social Sciences (SPSS) independent t-test version 16.0. The results showed that t = 0.467, df = 103, p = 0.048 and the Sig. (2-tailed) value is 0.641. Since sig. (2-tailed) value is greater than 0.05, it can be concluded that there is no statistical significant difference between the experimental group and the control group. / Science and Technology Education / M. Sc. (Mathematics, Science & Technology Education)