Aromaticity Pseudo Aromaticity Anti Aromaticity

Aromaticity and Antiaromaticity A comprehensive review of the science of aromaticity, as well as its evolution, from benzene to atomic clusters In Aromaticity and Antiaromaticity: Concepts and Applications, a team of accomplished chemists delivers a comprehensive exploration of the evolution and critical aspects of aromaticity. The book examines the new global criteria used to evaluate aromaticity, including the Nucleus Independent Chemical Shift (NICS) index and the electronic indices based on electronic properties. Additional discussions of inorganic aromatic compounds developed in this century, which give rise to new concepts like multifold aromaticity, are included. Three-dimensional aromaticity found in fullerenes and nanotubes, Möbius aromaticity present in some annulenes, and excited state aromaticity are explored as well. This volume explores the geometrical, electronic, magnetic, and thermodynamic characteristics of aromatic and antiaromatic compounds and their reactivity properties. It also provides: A thorough historical overview of aromaticity, as well as simple electronic and structural models Comprehensive explorations of organic and inorganic aromatic compounds, concepts of stability and reactivity, and geometric, energetic, magnetic, and electronic criteria of descriptors of aromaticity Practical discussions of heteroaromaticity, as well as Möbius aromaticity and excited state aromaticity In-depth examinations of sigma, pi, delta, and phi aromaticity Perfect for graduate students, researchers, and academics interested in aromaticity, organometallic chemistry, and computational chemistry, Aromaticity and Antiaromaticity: Concepts and Applications will also earn a place in the libraries of professionals and researchers working in organic, inorganic, and physical chemistry.

Designed to assist chemists in integrating the results of calculations on molecules and ions into their general body of chemical knowledge. Contains recent contributions from theoretical and computational chemistry to the development of the concept of aromaticity (antiaromaticity) and its expansion into new areas such as organometallic and cluster compounds and three-dimensional structures. Updates the modern status of aromaticity and covers basic principles and experimental applications.

Examines aromaticity through the historical and conceptual framework of simple molecular orbital theory. This approach is unique in that theoretical considerations are integrated with experimental observations. The criteria for aromatic, antiaromatic and nonaromatic compounds are discussed in with reference to benzene, cyclobutadiene and cyclooctatetraene. Also includes a chapter on the likely classes of aromatic compounds.

Metal clusters, an intermediate state between molecules and the extended solid, show peculiar bonding and reactivity patterns. Their significance is critical to many areas, including air pollution, interstellar matter, clay minerals, photography, catalysis, quantum dots, and virus crystals. In Aromaticity and Metal Clusters, dozens of international experts explore not only the basic aspects of aromaticity, but also the structures, properties, reactivity, stability, and other consequences of the aromaticity of a variety of metal clusters. Although the concept of aromaticity has been known for nearly two centuries, there is no way to measure it experimentally and no theoretical formula to calculate it. In order to gain insight into its exact nature, the authors of this volume examine various indirect characteristics such as geometrical, electronic, magnetic, thermodynamic, and reactivity considerations. The book begins by discussing the evolution of aromaticity from benzene to atomic clusters. Next, more specialized chapters focus on areas of significant interest. Topics discussed include: Computational studies on molecules with unusual aromaticity Electronic shells and magnetism in small metal clusters A density functional investigation on the structures, energetics, and properties of sodium clusters through electrostatic guidelines and molecular tailoring The correlation between electron delocalization and ring currents in all metallic aromatic compounds Phenomenological shell model and aromaticity in metal clusters Rationalizing the aromaticity indexes used to describe the aromatic behavior of metal clusters 5f orbital successive aromatic and antiaromatic zones in triangular uranium cluster chemistry This collection of diverse contributions, composed of the work of scientists worldwide, is destined to not only answer puzzling questions about the nature of aromaticity, but also to provoke further inquiry in the minds of researchers.

Aromaticity is a notion that appeared in the mid-nineteenth century to differentiate between unsaturated hydrocarbons and formally unsaturated benzene [1–3]. At the end of the nineteenth century it seemed that cyclicity was a necessary condition for differentiation between the two, but at the beginning of the twentieth century it turned out that the above assumption was not correct because cyclooctatetraene exhibited typical properties known for polyenes [4]. The essential property of b- zene-like compounds, often identified with aromatic compounds, was low react- ity. Hence thermodynamic stability was defined as resonance energy [5, 6] and was the first quantitative measure of aromaticity. Many theoretical approaches were proposed later to estimate this quantity, and now the criterion is often considered to be the most fundamental [7]. Almost at the same time, magnetic susceptibility was used to describe aromaticity [8, 9]. Consequently, many concepts based on mag- tism were developed, probably the most effective in assessment of aromaticity being nucleus independent chemical shift (NICS) [10] or Fowler’s maps of ring currents [11]. The criterion served Schleyer as a basis for a definition of aromat- ity: “Compounds which exhibit significantly exalted diamagnetic susceptibility are aromatic. Cyclic delocalisation may also result in bond length equalization, abn- mal chemical shifts and magnetic anisotropies, as well as chemical and physical properties which reflect energetic stabilisation”[12].

Advances in Quantum Chemistry, Volume 77, presents surveys of current topics in this rapidly developing field, one that has emerged at the cross section of the historically established areas of mathematics, physics, chemistry and biology. It features detailed reviews written by leading international researchers, with this release focusing on topics such as Per-Olov Löwdin's Impact on a 'Lost Son', Electron impact ionization cross sections for inner L- and M-subshells of atomic targets at relativistic energies, Aromaticity Revisited, Electron-atom and electron-molecule resonances, Precise Born-Oppenheimer potentials of the excited states of H_2 using explicitly correlated exponential functions, and more. Presents surveys of current topics in this rapidly-developing field that has emerged at the cross section of the historically established areas of mathematics, physics, chemistry and biology Features detailed reviews written by leading international researchers

Organophosphorus chemistry is an important discipline within organic chemistry. Phosphorus compounds, such as phosphines, trialkyl phosphites, phosphine oxides (chalcogenides), phosphonates, phosphinates and >P(O)H species, etc., may be important starting materials or intermediates in syntheses. Let us mention the Wittig reaction and the related transformations, the Arbuzov- and the Pudovik reactions, the Kabachnik–Fields condensation, the Hirao reaction, the Mitsunobu reaction, etc. Other reactions, e.g., homogeneous catalytic transformations or C-C coupling reactions involve P-ligands in transition metal (Pt, Pd, etc.) complex catalysts. The synthesis of chiral organophosphorus compounds means a continuous challenge. Methods have been elaborated for the resolution of tertiary phosphine oxides and for stereoselective organophosphorus transformations. P-heterocyclic compounds, including aromatic and bridged derivatives, P-functionalized macrocycles, dendrimers and low coordinated P-fragments, are also of interest. An important segment of organophosphorus chemistry is the pool of biologically-active compounds that are searched and used as drugs, or as plant-protecting agents. The natural analogue of P-compounds may also be mentioned. Many new phosphine oxides, phosphinates, phosphonates and phosphoric esters have been described, which may find application on a broad scale. Phase transfer catalysis, ionic liquids and detergents also have connections to phosphorus chemistry. Green chemical aspects of organophosphorus chemistry (e.g., microwave-assisted syntheses, solvent-free accomplishments, optimizations, and atom-efficient syntheses) represent a dynamically developing field. Last, but not least, theoretical approaches and computational chemistry are also a strong sub-discipline within organophosphorus chemistry.