Добірка наукової літератури з теми "Pyramidalization angle"

By using the pyramidalization angle as a localized geometric descriptor for oxygen reduction reaction (ORR) activity of carbon nanotubes (CNTs), we show the ORR activity of these systems can be readily predicted with mere structural optimization of CNTs.

AbstractNumerous highly curved fragments of C60 and unique subunits of C70 were synthesized under mild conditions using metal-catalyzed protocols. According to X-ray crystallographic analyses, highly curved fragments of C60 have a maximum π-orbital axis vector (POAV) pyramidalization angle of up to 12.9 °, whereas distinctive fragments of C70, analogous to the tube portion of the rugby-shaped buckyball, are less curved. Among the eight buckybowls studied herein, five form polar crystals. Depending on the molecular geometry, the inversion dynamics of buckybowls involves either a planar or an S-shaped (non-planar) transition structure.

The formulation that the title compound, C18H18N2O4S2, adopts is a zwitterionic core with the charge separated to the sulfilimine S and N atoms and is supported by the two different S—N bond distances about the sulfinimine N atom [1.594 (2) and 1.631 (2) Å, respectively] that are typical for such bonds. The notably unusual bond is S—N(oxazolidinone) [1.692 (2) Å] that is longer than a typical S—N bond [1.603 (18) Å,Mogulanalysis; Macraeet al.(2008).J. Appl. Cryst.41, 466–470]. The bond-angle sum about sulfilimine sulfur (308.35°) reflects the trigonal–pyramidal geometry of this atom. Two of the angles are less than 100°. Despite the pyramidalization of this sulfur, there are no significant intermolecular interactions, beyond usual van der Waals contacts, in the crystal packing.

Fullerenes that violate the isolated pentagon rule are too reactive and were obtained only as endoor exohedral derivatives. Density functional theory using the B3LYP hybrid density functional was applied to investigate the electronic and structural properties of the ten smallest tetrahedral (Td or T point group) fullerenes containing four directly fused pentagon-triples. The influence of nitrogen doping and exohedral hydrogenation of the four reactive sites was also analyzed. Nucleus independent chemical shifts values computed using B3LYP/6-31G(d) are used as global and local aromaticity probe. The global strain energy is evaluated in terms of the pyramidalization (POAV) angle. The results show that the stability increases with the elimination of the energetically unfavorable strain.

The asymmetric unit of the title salt, C5H8N3+·Cl−, comprises one half of the 2,6-diaminopyridinium cation (the other half being completed by the application of mirror symmetry) and one Cl−counter-anion, also located on the mirror plane. The amino N atom shows a significant pyramidalization, with a dihedral angle of 30.4 (14)° between the least-squares planes of the amino group and the non-H atoms of the 2,6-diaminopyridinium moiety. In the crystal, the cationic molecules and Cl−counter-anions are arranged in sheets parallel to (001) consisting of alternating polar and non-polar parts associated with the the Cl−anions, pyridinium and amino moieties, and the pyridine rings, respectively. N—H...Cl interactions within the polar part, as well as slipped π–π interactions in the non-polar part, help to establish the three-dimensional network.

Construction of periodic fulleroids (including covering polygons other than the classical pentagons and hexagons) is achieved by several coupling procedures. A constitutive typing enumeration for topologically periodic fulleroids is given. π-electronic periodicity of several series of tubulenes is rationalized in terms of some "rules of thumb". The strain energy of these nonplanar molecules was evaluated from the pyramidalization angles of the sp2 carbon atoms by the POAV1 procedure. Semiempirical PM3 calculations support the presented spectral data.

Cette thèse est le fruit de 3 années de travail reposant sur le sujet intitulé : "Chimie Structurale et Electronique: Rôle des Symétries et de la Courbure".L’originalité de la thématique abordée dans ce travail se trouve dans la pluridisciplinarité du sujet qui fait appel à la fois aux chimistes théoriciens et aux mathématiciens. Une importante partie des travaux se base sur la compréhension de la chimie théorique et de son utilisation par modélisation.Un des objectif alloué à ce travail, est la compréhension des systèmes moléculaires par des outils géométriques principalement initiés par Robert C. Haddon dès 1997. Nous avons tout d’abord pro- posé une clarification et une généralisation de ces outils basées sur des matériaux carbonés comme les fullerènes dont l’étude des caractéristiques topologiques est largement exploitée dans ce manuscrit. L’ensemble des points théoriques et des outils développés (l’angle de pyramidalisation, la courbure sphérique, le défaut angulaire, et l’hybridation) ont été largement illustrés avec des cartographies par l’utilisation d’outils de programmation et de logiciels qui ont permis l’étude de la déformation, de la courbure et l’étude des propriétés chimiques et physiques des systèmes.L’utilisation des outils issus de ce travail devrait permettre de pouvoir faciliter la modélisation de molécules sans limitation de tailles et pour des systèmes dont la modélisation par des calculs ab-initio ou DFT reste inaccessible.Nous avons également cherché à montrer le lien pouvant exister entre la géométrie des systèmes et l’information orbitalaire. Nous nous sommes intéressés à titre d’exemples à de nombreux systèmes pour la plupart carbonés et potentiellement aromatiques.Enfin, nous avons proposés l’étude des critères d’aromaticité suivant les théories énoncées entre autre par Hückel. Par cette étude, nous nous sommes penchés sur des systèmes linéaires moins connus i.e. les [n]-cumulènes qui présentent en particulier la curiosité de posséder des orbitales hélicoïdales. Nous avons établis les critères d’apparition de ce type d’hélices en fonction de la symétrie moléculaire.Le but in fine de ce travail, était de réussir à faire le lien entre des caractéristiques topologiques et la réactivité chimique de ces molécules et matériaux
This thesis is the result of 3 years of work based on the subject: "Structural and Electronic Chemistry: Role of Symmetries and Curvature".The originality of the topic consists in the multidisciplinary nature of the subject which involves both chemists theoreticians and mathematicians. An important part of the work is based on the under- standing of theoretical chemistry and its use by modeling.One of the objectives attributed to this work, is the understanding of molecular systems by geomet- rical tools mainly initiated by Robert C. Haddon in 1997. We first propose a clarification and a generalization of these tools based on carbon materials such as fullerenes whose study of topological characteristics is largely exploited in this manuscript.All the theoretical points and tools developed (the pyramidalization angle, the spherical curvature, the angular defect, and the hybridization) are widely illustrated with cartographies by the use of programming tools and softwares which provide the study of the deformation, the curvature and the investigation of the chemical and physical properties of the systems.The use of the tools resulting from this work will facilitate the simulation of molecules without size limitation and for systems whose modelisation by ab-initio or DFT calculations remains inaccessible. We also tried to show the relation which could exist between the geometry of the systems and the orbital information. We were interested in many systems as examples most of them are carbon-based and potentially aromatic.Consequently, we propose the study of the criteria of aromaticity according to the theories stated among others by Hückel. By this study, we focus on less known linear systems: the [n]-cumulenes which present the curiosity of helical orbitals. We established the criteria for the existence of this type of helices according to the molecular symmetry.The aim in fine was to establish the link between the topological characteristics and the chemical reactivity of these molecules and materials