Why 1,2‑quinone derivatives are more stable than their 2,3‑analogues?

In this work, we have studied the relative stability of 1,2- and 2,3-quinones. While 1,2-quinones have a closed-shell singlet ground state, the ground state for the studied 2,3-isomers is open-shell singlet, except for 2,3-naphthaquinone that has a closed-shell singlet ground state. In all cases, 1,2-quinones are more stable than their 2,3-counterparts. We analyzed the reasons for the higher stability of the 1,2-isomers through energy decomposition analysis in the framework of Kohn–Sham molecular orbital theory. The results showed that we have to trace the origin of 1,2-quinones’ enhanced stability to the more efficient bonding in the π-electron system due to more favorable overlap between the SOMOπ of the ·C4n−2H2n–CH·· and ··CH–CO–CO· fragments in the 1,2-arrangement. Furthermore, whereas 1,2-quinones present a constant trend with their elongation for all analyzed properties (geometric, energetic, and electronic), 2,3-quinone derivatives present a substantial breaking in monotonicity.European Union in the framework of European Social Fund through the Warsaw University of Technology Development Programme. O.A. S., H. S. and T.M. K

Perimeter ring currents in benzenoids from Pauling bond orders

It is shown that the ring currents in perimeter hexagonal rings of Kekulean benzenoids, as estimated within the Randić conjugated-circuit model, can be calculated directly without tedious pairwise comparison of Kekulé structures or Kekulé counting for cycle-deleted subgraphs. Required are only the Pauling bond orders of perimeter bonds and the number of Kekulé structures of the benzenoid, both readily available from the adjacency matrix of the carbon skeleton. This approach provides easy calculation of complete current maps for benzenoids in which every face has at least one bond on the perimeter (as in the example of cata-condensed benzenoids), and allows qualitative evaluation of the main ring-current contributions to 1H chemical shifts in general benzenoids. A combined Randić- Pauling model for correlation of ring current and bond length through bond order is derived and shown to be consistent with resilience of current under bond alternation

The topology of fullerenes

Fullerenes are carbon molecules that form polyhedral cages. Their bond structures are exactly the planar cubic graphs that have only pentagon and hexagon faces. Strikingly, a number of chemical properties of a fullerene can be derived from its graph structure. A rich mathematics of cubic planar graphs and fullerene graphs has grown since they were studied by Goldberg, Coxeter, and others in the early 20th century, and many mathematical properties of fullerenes have found simple and beautiful solutions. Yet many interesting chemical and mathematical problems in the field remain open. In this paper, we present a general overview of recent topological and graph theoretical developments in fullerene research over the past two decades, describing both solved and open problems. WIREs Comput Mol Sci 2015, 5:96–145. doi: 10.1002/wcms.1207 Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website

Currents in Carbon and Heterocyclic Networks

Current density maps are calculated within the ipsocentric approach for a variety of systems, to determine the nature of their aromatic magnetic response, and to probe the underlying principles governing ring current aromaticity. The first chapter briefly discusses the history of the term aromaticity, from the discovery of benzene, to ring current theory, the modern quantum mechanical ipsocentric approach, and the simple but powerful selection rules that are derived from it. Examples of systems displaying aromatic, antiaromatic and localised, non aromatic responses are provided in Chapter 2 to demonstrate the utility of the method, and the in depth analysis of aromaticity that it permits. Chapter 3 explores the possibility of designing tailored ring current responses on finite nanographene flakes via functionalisation by examining a variety of nanographene/nanographane hybrids derived from coronene and ovalene. This idea is extended in Chapter 4, by consideration of substitution of C6 cycles for borazine like B3N3 cycles, creating benzenoid/borazinoid hybrids. Chapter 5 investigates how BN heteroannulenes can be successfully aromatised by alteration of electronic charge. The approaches for altering current response introduced in Chapters 3 to 5 are unified in Chapter 6 in a case study of pyrene and structures derived from it by variation of charge, substitution, and functionalisation. Chapter 7 further examines how changing the electronic environment by substitution of carbon centres for heteroatoms alters ring current patterns, using linear polyacenes as the example systems. Chapter 8 moves away from the methods of controlling ring current by chemical manipulation and considers the effects of geometric change on aromaticity of the homotropenylium cation and the extended family of N homoannulenes. A brief discussion of the possibilities of designing aromatic systems using extended non standard ring architectures concludes the thesis

Volatile Messenger of Death - Grapevine Fatty Acid Hydroperoxide Lyase Acts in Cell-Death Related Immunity

Grapevine is a widespread and valuable agricultural crop, but easily infected by plant pathogens. Oxylipins are fatty acid-derived compounds acting as important signal molecules in plant responses to biotic and abiotic stresses

Electronic tailoring of graphene nanostructures via on-surface synthesis

121 p.Esta tesis presenta un estudio exhaustivo de las propiedades electrónicas de diversas clases de nanocintas de grafeno (GNRs) producidas mediante métodos de síntesis en superficie de oro. El estudio de estas cintas ha sido realizado mediante Microscopía y Espectroscopía de Efecto Túnel a bajas temperaturas (LT-STM/STS) y en condiciones de ultra alto vacío. Otros resultados adicionales fueron obtenidos mediante cálculos ab initio de Teoría del Funcional de la Densidad (DFT), en el grupo del Prof. DanielSánchez-Portal. Los nuevos precursores moleculares usados en esta tesis fueron sintetizados por el grupo del Prof. Diego Peña y el grupo de Yamaguchi-Sensei.Para conseguir un alto grado de control en la estructura de los GNRs, crecemos nuestras cintas usando precursores moleculares específicamente diseñados para actuar como bloques básicos de construcción. Las nanocintas resultantes, con una estructura precisa a la escala atómica, se obtienen mediante la activación de reacciones catalizadas por la superficie, típicamente oro. Este método de síntesis en superficie ha producido sistemas modelo que facilitaron el estudio de las propiedades electrónicas de las nanocintas de grafeno armchair de ancho 7 (7-AGNRs), dos especies de 7-AGNR modificados químicamente y nanocintas híbridas crecidas mediante la combinación de secciones prístinas y secciones modificadas con boro.CICnanoGUN

Development and Mechanistic Study of Photoredox Systems

Herein is described the development of a novel methodology utilizing photoredox catalysis along with a corresponding mechanistic analysis of this method. Additionally, the results of a mechanistic study of a separate methodology are also reported, revealing important details about the design and stability of photoredox dyes. The development of a photoredox-mediated Newman-Kwart rearrangement is first described. This work was conducted jointly with Dr. Andrew Perkowski. The Newman-Kwart Rearrangement is a reliable methodology for the synthesis of aryl thiols. However the extreme thermal energy required for the reaction presents a challenge for heavily modified substrates. The development of a more mild set of reaction conditions represents an advancement in this field and allows for the facile synthesis of previously difficult to access substrates. Following the development of the methodology, an investigation into the factors affecting reactivity was achieved. Through a combination of spectroscopic and kinetic analyses the photoredox Newman-Kwart rearrangement was found to strongly couple reactivity with substrate electronics. Furthermore, the reactive intermediate was characterized as a thione cation-radical which is best described as a thiyl-radical. Using thermochemical data, a predictive model for successful rearrangement was developed and displays excellent agreement with experimental results. Finally, the elucidation of key reaction dynamics for an arene C-H functionalization reaction mediated by photoredox catalysis is described. Importantly, both the reaction mechanism as well as important factors governing catalyst efficiency were discovered. The understanding of this reaction manifold could allow for the development of other methodologies that access additional important structural motifs. More broadly, the results concerning acridinium stability and efficiency could be used to improve reactivity in a number of photoredox systems, not just those related to oxidative arene functionalizations.Doctor of Philosoph