Unravelling [3+2] Cycloaddition Reactions through the Molecular Electron Density Theory

Después de la primera clasificación de las reacciones 32CA en reacciones de tipo zw y pr, establecidas en el año 2014, la estructura y reactividad de los TACs más importantes utilizados en las reacciones 32CA ha sido completamente caracterizado en base a la MEDT propuesta recientemente. Entre la gran cantidad de trabajo desarrollado a lo largo de la presente tesis doctoral, se han seleccionado y discutido ocho publicaciones representativas, que permitieron caracterizar dos nuevos tipos de reactividad y consolidar la reactividad original de tipo zw. Así, dependiendo de las cuatro estructuras electrónicas diferentes de los TACs, es decir, pseudodiradical, pseudoradical, carbenoide y zwitteriónica, las reacciones 32CA se han clasificado en reacciones de tipo pdr, pmr, cb y zw. Mientras que las reacciones 32CA de tipo pdr son las más rápidas, las reacciones de tipo zw son las más lentas. Las diferentes estructuras electrónicas en el estado fundamental de los reactivos explican esta tendencia de reactividad y revelan que la reactividad de los TACs carbenoides es diferente. Además, ningún TAC puede considerarse una estructura 1,2-zwitteriónica, tal y como se propone para los “1,3-dipolos”. El carácter polar de la reacción, medido por el valor de la GEDT calculado en la estructura del TS, afecta a los cuatro tipos de reactividad, de tal forma que cuanto más fuertes sean las interacciones nucleofílicas / electrofílicas que tienen lugar en el TS, más rápida es la reacción, e incluso puede cambiar el mecanismo molecular de acuerdo con las funciones de Parr definidas dentro de la CDFT. Esta racionalización basada en la MEDT de las reacciones 32CA esclarece las propuestas mecanísticas de Huisgen y Firestone establecidas en los años 60. Independientemente del tipo de reactividad y el carácter polar de la reacción, el análisis topológico de la ELF a lo largo de las reacciones 32CA que tienen lugar en un solo paso sugiere que los cambios de enlace no son “concertados” sino secuenciales, descartando así la clasificación de estas reacciones como “pericíclicas”. En la presente tesis doctoral, la teoría clásica de las reacciones 32CA, establecida en los años 60 del siglo pasado y que aún prevalece en la actualidad, es revisitada y reinterpretada en base a la MEDT. Se establece un nuevo y sólido modelo de reactividad para las reacciones 32CA, enfatizando que la visión actual de la química orgánica necesita replantearse en base al análisis de la densidad electrónica.After the first classification of [3+2] cycloaddition (32CA) reactions into zw-type and pr-type reactions, established in 2014, the structure and reactivity of the most important three-atom-components (TACs) used in 32CA reactions has been completely characterised within the recently proposed Molecular Electron Density Theory (MEDT). Among the huge amount of work developed along the present Ph.D thesis, eight representative publications have been selected and discussed herein, which allowed characterising two new reactivity types as well as consolidating the original zw-type reactivity. Thus, depending on the four different electronic structures of TACs, i.e. pseudodiradical, pseudoradical, carbenoid and zwitterionic, 32CA reactions have been classified into pdr-, pmr-, cb- and zw-type reactions. While pdr-type 32CA reactions are the fastest, zw-type reactions are the slowest. The different electronic structures at the ground state of the reagents account for this reactivity trend and reveal that the reactivity of carbenoid TACs is different. In addition, no TAC can be considered a 1,2-zwitterionic structure as proposed for “1,3-dipoles”. The polar character of the reaction, measured by the global electron density transfer value computed at the transition state structure (TS), affects the four reactivity types in such a manner that the stronger the nucleophilic/electrophilic interactions taking place at the TS, the faster the reaction, and may even change the molecular mechanism according to the Parr functions defined within Conceptual DFT. This MEDT rationalisation of 32CA reactions unravels classical Huisgen’s and Firestone’s mechanistic proposals established in the 60’s. Regardless of the reactivity type and polar character of the reaction, topological analysis of the electron localisation function along one-step 32CA reactions suggests that the bonding changes are not “concerted”, but sequential, thus ruling out the classification of these reactions as “pericyclic”. In the present thesis, the classical theory of 32CA reactions, established in the 60’s of the past century and still prevailing today, is revisited and reinterpreted based on MEDT. A solid new reactivity model for 32CA reactions is established, emphasising that the way that organic chemists conceive organic chemistry demands a contemporary revision aimed towards the analysis of electron density

Investigation of Absolute Photoionization Cross Sections of Cyclic Ketones, Low Temperature Combustion of Propargylamine by Synchrotron Photoionization Mass Spectrometry, and Computational Study of Hypersalts

The presented research was carried out at the University of San Francisco. Measurements of absolute photoionization cross sections of both cyclopentanone and cyclohexanone, as well as the Cl-initiated oxidation of propargylamine were completed through the use of a multiplexed photoionization mass spectrometer (MPMIS) located at the Lawrence Berkeley National Laboratory Advanced Light Source (ALS). Furthermore, the design of novel LiF containing hypersalts, constructed from superhalogens and superalkalis, were explored due to their enhanced ionization energies and electron affinities. All determined calculations were completed using the CBS-QB3 composite model with the Gaussian09 program

Redox-active ligand uranium complexes for approaches to multi-electron chemistry

While transition metal complexes are known to participate in multi-electron redox chemistry to facilitate important organometallic transformations, actinides, due to their low redox potentials, have a propensity to perform single electron chemistry. Because of its highly reducing nature, the ability to control the electronics of low-valent uranium is highly sought after as this may lead to unprecedented reactivity. Our lab has specifically been interested in mediating multi-electron transformations at uranium by employing redox-active ligands. Redox-active ligands can be used to facilitate multi-electron processes such as oxidative addition and reductive elimination at single metal centers. Using primarily 2,6-((Mes)N=CMe)2C5H3N) ( MesPDIMe) as a redox-active ligand, highly reduced uranium species bearing bulky cyclopentadienyl-based ancillary ligands, CpxU (MesPDIMe)(L) (x = P (1-(7,7-dimethylbenzyl)), * (1,2,3,4,5-pentamethyl); L = THF, HMPA), have been synthesized. These species have the ability to perform one, two, and four electron reduction of a variety of substrates. For examples, uranium mediated pinacol coupling of carbonylated substrates as well as oxidative addition toward two (X2, PhE-EPh, PhE-X) and four electron (Ar-N=N-Ar’, oxygen-atom transfer reagents) organic oxidants have been studied. with both radical and concerted addition pathways operable. Synthesis of a trans-dioxo species, Cp*UO2(MesPDIMe), has allowed for the study of the activation of the robust U=O double bonds—providing key insights into the necessary components for U=O bond scission. The lessons learned from the reductive silylation of this complex redox-active ligand species has allowed for application of these principles to simple UO 22+ systems

Computational mechanistic photochemistry: The central role of conical intersections

In this thesis, I review my own contributions in the field of computational photochemistry. This manuscript is written as an introduction to this field of research. It is not intended to be a textbook, as more emphasis has been made on illustrations rather than on methodologies and technical guidelines. In this way, I hope that it will be accessible to a large audience, from undergraduate students to more experienced scientists who would be interested in learning about this fascinating and relatively young field of research

The Halogen Bond

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design

Coumarins: their versatile use in photoredox catalysis and biological applications.

Coumarin dyes have proven to posses unique photophysical properties thanks to the high quantum yield, and stability and an absorption and emission which cover the most part of the visible spectrum. In particular, a peculiar characteristic of this class of fluorophores is the large Stokes shift. Thanks to these exceptional photophysical properties, coumarin dyes are widespread used in different applications including fluorescent bio-label, emitting materials in OLED and dyes in solar cells as example. To the best of our knowledge their systematic use in photoredox catalysis has not been explore yet. This research aimed at the design, the synthesis, the photophysical characterization of new LSS coumarin dyes and their use in different fields such as photoredox catalysis, photopolymerization and biological applications (bioconiugation and fluorescent microscopy)

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photo-activatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review

Molecular Photochemistry

There have been various comprehensive and stand-alone text books on the introduction to Molecular Photochemistry which provide crystal clear concepts on fundamental issues. This book entitled "Molecular Photochemistry - Various Aspects" presents various advanced topics that inherently utilizes those core concepts/techniques to various advanced fields of photochemistry and are generally not available. The purpose of publication of this book is actually an effort to bring many such important topics clubbed together. The goal of this book is to familiarize both research scholars and post graduate students with recent advancement in various fields related to Photochemistry. The book is broadly divided in five parts: the photochemistry I) in solution, II) of metal oxides, III) in biology, IV) the computational aspects and V) applications. Each part provides unique aspect of photochemistry. These exciting chapters clearly indicate that the future of photochemistry like in any other burgeoning field is more exciting than the past

Novel photocatalytic organic synthesis : cyclization and N-alkylation of nitroaromatic compounds

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