Executive Summary of the Biodata of Dr. Eluvathingal D. Jemmis Education
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Introduction to Aromaticity
Introduction to Aromaticity Historical Timeline:1 Spotlight on Benzene:2 th • Early 19 century chemists derive benzene formula (C6H6) and molecular mass (78). • Carbon to hydrogen ratio of 1:1 suggests high reactivity and instability. • However, benzene is fairly inert and fails to undergo reactions that characterize normal alkenes. - Benzene remains inert at room temperature. - Benzene is more resistant to catalytic hydrogenation than other alkenes. Possible (but wrong) benzene structures:3 Dewar benzene Prismane Fulvene 2,4- Hexadiyne - Rearranges to benzene at - Rearranges to - Undergoes catalytic - Undergoes catalytic room temperature. Faraday’s benzene. hydrogenation easily. hydrogenation easily - Lots of ring strain. - Lots of ring strain. - Lots of ring strain. 1 Timeline is computer-generated, compiled with information from pg. 594 of Bruice, Organic Chemistry, 4th Edition, Ch. 15.2, and from Chemistry 14C Thinkbook by Dr. Steven Hardinger, Version 4, p. 26 2 Chemistry 14C Thinkbook, p. 26 3 Images of Dewar benzene, prismane, fulvene, and 2,4-Hexadiyne taken from Chemistry 14C Thinkbook, p. 26. Kekulé’s solution: - “snake bites its own tail” (4) Problems with Kekulé’s solution: • If Kekulé’s structure were to have two chloride substituents replacing two hydrogen atoms, there should be a pair of 1,2-dichlorobenzene isomers: one isomer with single bonds separating the Cl atoms, and another with double bonds separating the Cl atoms. • These isomers were never isolated or detected. • Rapid equilibrium proposed, where isomers interconvert so quickly that they cannot be isolated or detected. • Regardless, Kekulé’s structure has C=C’s and normal alkene reactions are still expected. - But the unusual stability of benzene still unexplained. -
On the Harmonic Oscillator Model of Electron Delocalization (HOMED) Index and Its Application to Heteroatomic Π-Electron Systems
Symmetry 2010, 2, 1485-1509; doi:10.3390/sym2031485 OPEN ACCESS symmetry ISSN 2073-8994 www.mdpi.com/journal/symmetry Article On the Harmonic Oscillator Model of Electron Delocalization (HOMED) Index and its Application to Heteroatomic π-Electron Systems Ewa D. Raczyñska 1, *, Małgorzata Hallman 1, Katarzyna Kolczyñska 2 and Tomasz M. Stêpniewski 2 1 Department of Chemistry, Warsaw University of Life Sciences (SGGW), ul. Nowoursynowska 159c, 02-776 Warszawa, Poland 2 Interdisciplinary Department of Biotechnology, Warsaw University of Life Sciences (SGGW), ul. Nowoursynowska 166, 02-776 Warszawa, Poland * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +48-22-59-37623; Fax: +49-22-59-37635. Received: 23 April 2010; in revised form: 19 May 2010 / Accepted: 7 July 2010 / Published: 12 July 2010 Abstract: The HOMA (Harmonic Oscillator Model of Aromaticity) index, reformulated in 1993, has been very often applied to describe π-electron delocalization for mono- and polycyclic π-electron systems. However, different measures of π-electron delocalization were employed for the CC, CX, and XY bonds, and this index seems to be inappropriate for compounds containing heteroatoms. In order to describe properly various resonance effects (σ-π hyperconjugation, n-π conjugation, π-π conjugation, and aromaticity) possible for heteroatomic π-electron systems, some modifications, based on the original HOMA idea, were proposed and tested for simple DFT structures containing C, N, and O atoms. An abbreviation HOMED was used for the modified index. Keywords: geometry-based index; π -electron delocalization; σ - π hyperconjugation; n-π conjugation; π-π conjugation; aromaticity; heteroatomic compounds; DFT 1. -
![And [Z–Hali]- Halogen Bonds: Electron Density Properties And](https://docslib.b-cdn.net/cover/6945/and-z-hali-halogen-bonds-electron-density-properties-and-166945.webp)
And [Z–Hali]- Halogen Bonds: Electron Density Properties And
molecules Article Strength of the [Z–I···Hal]− and [Z–Hal···I]− Halogen Bonds: Electron Density Properties and Halogen Bond Length as Estimators of Interaction Energy Maxim L. Kuznetsov 1,2 1 Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais, 1049-001 Lisbon, Portugal; [email protected]; Tel.: +351-218-419-236 2 Institute of Chemistry, Saint Petersburg State University, Universitetskaya Nab. 7/9, 199034 Saint Petersburg, Russia Abstract: Bond energy is the main characteristic of chemical bonds in general and of non-covalent interactions in particular. Simple methods of express estimates of the interaction energy, Eint, us- ing relationships between Eint and a property which is easily accessible from experiment is of great importance for the characterization of non-covalent interactions. In this work, practically important relationships between Eint and electron density, its Laplacian, curvature, potential, kinetic, and total energy densities at the bond critical point as well as bond length were derived for the structures of the [Z–I···Hal]− and [Z–Hal···I]− types bearing halogen bonds and involving iodine as interact- ing atom(s) (totally 412 structures). The mean absolute deviations for the correlations found were 2.06–4.76 kcal/mol. Keywords: bond critical point properties; interaction energy; bond energy; bond strength; den- sity functional theory; electron density; energy density; halogen bond; QTAIM Citation: Kuznetsov, M.L. Strength of the [Z–I···Hal]− and [Z–Hal···I]− Halogen Bonds: Electron Density Properties and Halogen Bond Length as Estimators of Interaction Energy. 1. Introduction Molecules 2021, 26, 2083. https:// The halogen bond is one of the most important types of non-covalent interactions doi.org/10.3390/molecules26072083 being second only to hydrogen bonds in its significance. -
Aromaticity Sem- Ii
AROMATICITY SEM- II In 1931, German chemist and physicist Sir Erich Hückel proposed a theory to help determine if a planar ring molecule would have aromatic properties .This is a very popular and useful rule to identify aromaticity in monocyclic conjugated compound. According to which a planar monocyclic conjugated system having ( 4n +2) delocalised (where, n = 0, 1, 2, .....) electrons are known as aromatic compound . For example: Benzene, Naphthalene, Furan, Pyrrole etc. Criteria for Aromaticity 1) The molecule is cyclic (a ring of atoms) 2) The molecule is planar (all atoms in the molecule lie in the same plane) 3) The molecule is fully conjugated (p orbitals at every atom in the ring) 4) The molecule has 4n+2 π electrons (n=0 or any positive integer Why 4n+2π Electrons? According to Hückel's Molecular Orbital Theory, a compound is particularly stable if all of its bonding molecular orbitals are filled with paired electrons. - This is true of aromatic compounds, meaning they are quite stable. - With aromatic compounds, 2 electrons fill the lowest energy molecular orbital, and 4 electrons fill each subsequent energy level (the number of subsequent energy levels is denoted by n), leaving all bonding orbitals filled and no anti-bonding orbitals occupied. This gives a total of 4n+2π electrons. - As for example: Benzene has 6π electrons. Its first 2π electrons fill the lowest energy orbital, and it has 4π electrons remaining. These 4 fill in the orbitals of the succeeding energy level. The criteria for Antiaromaticity are as follows: 1) The molecule must be cyclic and completely conjugated 2) The molecule must be planar. -
A New Way for Probing Bond Strength J
A New Way for Probing Bond Strength J. Klein, H. Khartabil, J.C. Boisson, J. Contreras-Garcia, Jean-Philip Piquemal, E. Henon To cite this version: J. Klein, H. Khartabil, J.C. Boisson, J. Contreras-Garcia, Jean-Philip Piquemal, et al.. A New Way for Probing Bond Strength. Journal of Physical Chemistry A, American Chemical Society, 2020, 124 (9), pp.1850-1860. 10.1021/acs.jpca.9b09845. hal-02377737 HAL Id: hal-02377737 https://hal.archives-ouvertes.fr/hal-02377737 Submitted on 27 Mar 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. A New Way for Probing Bond Strength Johanna Klein,y Hassan Khartabil,y Jean-Charles Boisson,z Julia Contreras-Garc´ıa,{ Jean-Philip Piquemal,{ and Eric H´enon∗,y yInstitut de Chimie Mol´eculaire de Reims UMR CNRS 7312, Universit´ede Reims Champagne-Ardenne, Moulin de la Housse 51687 Reims Cedex 02 BP39 (France) zCReSTIC EA 3804, Universit´ede Reims Champagne-Ardenne, Moulin de la Housse 51687 Reims Cedex 02 BP39 (France) {Sorbonne Universit´es,UPMC, Laboratoire de Chimie Th´eoriqueand UMR CNRS 7616, 4 Pl Jussieu, 75252 Paris Cedex 05(France) E-mail: [email protected] Phone: +33(3)26918497 1 Abstract The covalent chemical bond is intimately linked to electron sharing between atoms. -
Graphene Supported Rhodium Nanoparticles for Enhanced Electrocatalytic Hydrogen Evolution Reaction Ameerunisha Begum1*, Moumita Bose2 & Golam Moula2
www.nature.com/scientificreports OPEN Graphene Supported Rhodium Nanoparticles for Enhanced Electrocatalytic Hydrogen Evolution Reaction Ameerunisha Begum1*, Moumita Bose2 & Golam Moula2 Current research on catalysts for proton exchange membrane fuel cells (PEMFC) is based on obtaining higher catalytic activity than platinum particle catalysts on porous carbon. In search of a more sustainable catalyst other than platinum for the catalytic conversion of water to hydrogen gas, a series of nanoparticles of transition metals viz., Rh, Co, Fe, Pt and their composites with functionalized graphene such as RhNPs@f-graphene, CoNPs@f-graphene, PtNPs@f-graphene were synthesized and characterized by SEM and TEM techniques. The SEM analysis indicates that the texture of RhNPs@f- graphene resemble the dispersion of water droplets on lotus leaf. TEM analysis indicates that RhNPs of <10 nm diameter are dispersed on the surface of f-graphene. The air-stable NPs and nanocomposites were used as electrocatalyts for conversion of acidic water to hydrogen gas. The composite RhNPs@f- graphene catalyses hydrogen gas evolution from water containing p-toluene sulphonic acid (p-TsOH) at an onset reduction potential, Ep, −0.117 V which is less than that of PtNPs@f-graphene (Ep, −0.380 V) under identical experimental conditions whereas the onset potential of CoNPs@f-graphene was at Ep, −0.97 V and the FeNPs@f-graphene displayed onset potential at Ep, −1.58 V. The pure rhodium nanoparticles, RhNPs also electrocatalyse at Ep, −0.186 V compared with that of PtNPs at Ep, −0.36 V and that of CoNPs at Ep, −0.98 V. -
Aromaticity in Polyhydride Complexes of Ru, Ir, Os, and Pt† Cite This: DOI: 10.1039/C5cp04330a Elisa Jimenez-Izala and Anastassia N
PCCP View Article Online PAPER View Journal r-Aromaticity in polyhydride complexes of Ru, Ir, Os, and Pt† Cite this: DOI: 10.1039/c5cp04330a Elisa Jimenez-Izala and Anastassia N. Alexandrova*ab Transition-metal hydrides represent a unique class of compounds, which are essential for catalysis, organic i À i À synthesis, and hydrogen storage. In this work we study IrH5(PPh3)2,(RuH5(P Pr3)2) ,(OsH5(PPr3)2) ,and À OsH4(PPhMe2)3 polyhydride complexes, inspired by the recent discovery of the s-aromatic PtZnH5 cluster À anion. The distinctive feature of these molecules is that, like in the PtZnH5 cluster, the metal is five-fold Received 23rd July 2015, coordinated in-plane, and holds additional ligands attheaxialpositions.Thisworkshowsthattheunusual Accepted 17th September 2015 coordination in these compounds indeed can be explained by s-aromaticity in the pentagonal arrangement, DOI: 10.1039/c5cp04330a stabilized by the atomic orbitals on the metal. Based on this newly elucidated bonding principle, we additionally propose a new family of polyhydrides that display a uniquely high coordination. We also report the first www.rsc.org/pccp indications of how aromaticity may impact the reactivity of these molecules. 1 Introduction many catalytic cycles, where they have either been used as catalysts or invoked as key intermediates.15,16 Aromaticity in Aromaticity is a very important concept in the contemporary general is associated with high symmetry, stability, and specific chemistry: the particular electronic structure of aromatic reactivity. Therefore, the stability of transition-metal hydride systems, where electrons are delocalized, explains their large complexes might have an important repercussion in the kinetics energetic stabilization and low reactivity. -
Halogen Bonds in Biological Molecules
Halogen bonds in biological molecules Pascal Auffinger†‡, Franklin A. Hays§, Eric Westhof†, and P. Shing Ho‡§ †Institut de Biologie Mole´culaire et Cellulaire, Centre National de la Recherche Scientifique, Unite´Propre de Recherche 9002, Universite´Louis Pasteur, 15 Rue Rene´Descartes, F-67084 Strasbourg, France; and §Department of Biochemistry and Biophysics, Agriculture͞Life Sciences Building, Room 2011, Oregon State University, Corvallis, OR 97331-7305 Communicated by K. E. van Holde, Oregon State University, Corvallis, OR, October 13, 2004 (received for review August 17, 2004) Short oxygen–halogen interactions have been known in organic chemistry since the 1950s and recently have been exploited in the design of supramolecular assemblies. The present survey of protein and nucleic acid structures reveals similar halogen bonds as po- tentially stabilizing inter- and intramolecular interactions that can affect ligand binding and molecular folding. A halogen bond in biomolecules can be defined as a short COX⅐⅐⅐OOY interaction (COX is a carbon-bonded chlorine, bromine, or iodine, and OOY is a carbonyl, hydroxyl, charged carboxylate, or phosphate group), where the X⅐⅐⅐O distance is less than or equal to the sums of the respective van der Waals radii (3.27 Å for Cl⅐⅐⅐O, 3.37Å for Br⅐⅐⅐O, and 3.50 Å for I⅐⅐⅐O) and can conform to the geometry seen in small molecules, with the COX⅐⅐⅐O angle Ϸ165° (consistent with a strong Fig. 1. Schematic of short halogen (X) interactions to various oxygen- directional polarization of the halogen) and the X⅐⅐⅐OOY angle containing functional groups (where OOY can be a carbonyl, hydroxyl, or Ϸ120°. -
Reactions of Aromatic Compounds Just Like an Alkene, Benzene Has Clouds of Electrons Above and Below Its Sigma Bond Framework
Reactions of Aromatic Compounds Just like an alkene, benzene has clouds of electrons above and below its sigma bond framework. Although the electrons are in a stable aromatic system, they are still available for reaction with strong electrophiles. This generates a carbocation which is resonance stabilized (but not aromatic). This cation is called a sigma complex because the electrophile is joined to the benzene ring through a new sigma bond. The sigma complex (also called an arenium ion) is not aromatic since it contains an sp3 carbon (which disrupts the required loop of p orbitals). Ch17 Reactions of Aromatic Compounds (landscape).docx Page1 The loss of aromaticity required to form the sigma complex explains the highly endothermic nature of the first step. (That is why we require strong electrophiles for reaction). The sigma complex wishes to regain its aromaticity, and it may do so by either a reversal of the first step (i.e. regenerate the starting material) or by loss of the proton on the sp3 carbon (leading to a substitution product). When a reaction proceeds this way, it is electrophilic aromatic substitution. There are a wide variety of electrophiles that can be introduced into a benzene ring in this way, and so electrophilic aromatic substitution is a very important method for the synthesis of substituted aromatic compounds. Ch17 Reactions of Aromatic Compounds (landscape).docx Page2 Bromination of Benzene Bromination follows the same general mechanism for the electrophilic aromatic substitution (EAS). Bromine itself is not electrophilic enough to react with benzene. But the addition of a strong Lewis acid (electron pair acceptor), such as FeBr3, catalyses the reaction, and leads to the substitution product. -
![Anagostic Interactions Under Pressure: Attractive Or Repulsive? Wolfgang Scherer *[A], Andrew C](https://docslib.b-cdn.net/cover/5995/anagostic-interactions-under-pressure-attractive-or-repulsive-wolfgang-scherer-a-andrew-c-885995.webp)
Anagostic Interactions Under Pressure: Attractive Or Repulsive? Wolfgang Scherer *[A], Andrew C
Manuscript Click here to download Manuscript: manuscript_final.pdf ((Attractive or repulsive?)) DOI: 10.1002/anie.200((will be filled in by the editorial staff)) Anagostic Interactions under Pressure: Attractive or Repulsive? Wolfgang Scherer *[a], Andrew C. Dunbar [a], José E. Barquera-Lozada [a], Dominik Schmitz [a], Georg Eickerling [a], Daniel Kratzert [b], Dietmar Stalke [b], Arianna Lanza [c,d], Piero Macchi*[c], Nicola P. M. Casati [d], Jihaan Ebad-Allah [a] and Christine Kuntscher [a] The term “anagostic interactions” was coined in 1990 by Lippard preagostic interactions are considered to lack any “involvement of 2 and coworkers to distinguish sterically enforced M•••H-C contacts dz orbitals in M•••H-C interactions” and rely mainly on M(dxz, yz) (M = Pd, Pt) in square-planar transition metal d8 complexes from o V (C-H) S-back donation.[3b] attractive, agostic interactions.[1a] This classification raised the fundamental question whether axial M•••H-C interaction in planar The first observation of unusual axial M•••H-C interaction in 8 8 d -ML4 complexes represent (i) repulsive anagostic 3c-4e M•••H-C planar d -ML4 complexes was made by S. Trofimenko, who interactions[1] (Scheme 1a) or (ii) attractive 3c-4e M•••H-C pioneered the chemistry of transition metal pyrazolylborato hydrogen bonds[2] (Scheme 1b) in which the transition metal plays complexes.[5,6] Trofimenko also realized in 1968, on the basis of the role of a hydrogen-bond acceptor (Scheme 1b). The latter NMR studies, that the shift of the pseudo axial methylene protons in 3 bonding description is related to another bonding concept which the agostic species [Mo{Et2B(pz)2}(K -allyl)(CO)2] (1) (pz = describes these M•••H-C contacts in terms of (iii) pregostic or pyrazolyl; allyl = H2CCHCH2) “is comparable in magnitude but [3] preagostic interactions (Scheme 1c) which are considered as being different in direction from that observed in Ni[Et2B(pz)2]2” (2) “on the way to becoming agostic, or agostic of the weak type”.[4] (Scheme 2).[6,7] Scheme 1. -
Binuclear Copper(I) Borohydride Complex Containing Bridging Bis
crystals Article Binuclear Copper(I) Borohydride Complex Containing Bridging Bis(diphenylphosphino) Methane Ligands: Polymorphic Structures of 2 [(µ2-dppm)2Cu2(η -BH4)2] Dichloromethane Solvate Natalia V. Belkova 1 ID , Igor E. Golub 1,2 ID , Evgenii I. Gutsul 1, Konstantin A. Lyssenko 1, Alexander S. Peregudov 1, Viktor D. Makhaev 3, Oleg A. Filippov 1 ID , Lina M. Epstein 1, Andrea Rossin 4 ID , Maurizio Peruzzini 4 and Elena S. Shubina 1,* ID 1 A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences (INEOS RAS), 119991 Moscow, Russia; [email protected] (N.V.B.); [email protected] (I.E.G.); [email protected] (E.I.G.); [email protected] (K.A.L.); [email protected] (A.S.P.); [email protected] (O.A.F.); [email protected] (L.M.E.) 2 Inorganic Chemistry Department, Peoples’ Friendship University of Russia (RUDN University), 117198 Moscow, Russia 3 Institute of Problems of Chemical Physics, Russian Academy of Sciences (IPCP RAS), 142432 Moscow, Russia; [email protected] 4 Istituto di Chimica dei Composti Organometallici Consiglio Nazionale delle Ricerche (ICCOM CNR), 50019 Sesto Fiorentino, Italy; [email protected] (A.R.); [email protected] (M.P.) * Correspondence: [email protected]; Tel.: +7-495-135-5085 Academic Editor: Sławomir J. Grabowski Received: 18 September 2017; Accepted: 17 October 2017; Published: 20 October 2017 Abstract: Bis(diphenylphosphino)methane copper(I) tetrahydroborate was synthesized by ligands exchange in bis(triphenylphosphine) copper(I) tetrahydroborate, and characterized by XRD, FTIR, NMR spectroscopy. According to XRD the title compound has dimeric structure, [(µ2-dppm)2Cu2(η2-BH4)2], and crystallizes as CH2Cl2 solvate in two polymorphic forms (orthorhombic, 1, and monoclinic, 2) The details of molecular geometry and the crystal-packing pattern in polymorphs were studied. -
Organometallics Study Meeting H.Mitsunuma 1
04/21/2011 Organometallics Study Meeting H.Mitsunuma 1. Crystal field theory (CFT) and ligand field theory (LFT) CFT: interaction between positively charged metal cation and negative charge on the non-bonding electrons of the ligand LFT: molecular orbital theory (back donation...etc) Octahedral (figure 9-1a) d-electrons closer to the ligands will have a higher energy than those further away which results in the d-orbitals splitting in energy. ligand field splitting parameter ( 0): energy between eg orbital and t2g orbital 1) high oxidation state 2) 3d<4d<5d 3) spectrochemical series I-< Br-< S2-< SCN-< Cl-< N -,F-< (H N) CO, OH-< ox, O2-< H O< NCS- <C H N, NH < H NCH CH NH < bpy, phen< NO - - - - 3 2 2 2 5 5 3 2 2 2 2 2 < CH3 ,C6H5 < CN <CO cf) pairing energy: energy cost of placing an electron into an already singly occupied orbital Low spin: If 0 is large, then the lower energy orbitals(t2g) are completely filled before population of the higher orbitals(eg) High spin: If 0 is small enough then it is easier to put electrons into the higher energy orbitals than it is to put two into the same low-energy orbital, because of the repulsion resulting from matching two electrons in the same orbital 3 n ex) (t2g) (eg) (n= 1,2) Tetrahedral (figure 9-1b), Square planar (figure 9-1c) LFT (figure 9-3, 9-4) - - Cl , Br : lower 0 (figure 9-4 a) CO: higher 0 (figure 9-4 b) 2. Ligand metal complex hapticity formal chargeelectron donation metal complex hapticity formal chargeelectron donation MR alkyl 1 -1 2 6-arene 6 0 6 MH hydride 1 -1 2 M MX H 1 -1 2 halogen 1 -1 2 M M -hydride M OR alkoxide 1 -1 2 X 1 -1 4 M M -halogen O R acyl 1 -1 2 O 1 -1 4 M R M M -alkoxide O 1-alkenyl 1 -1 2 C -carbonyl 1 0 2 M M M R2 C -alkylidene 1 -2 4 1-allyl 1 -1 2 M M M O C 3-carbonyl 1 0 2 M R acetylide 1 -1 2 MMM R R C 3-alkylidine 1 -3 6 M carbene 1 0 2 MMM R R M carbene 1 -2 4 R M carbyne 1 -3 6 M CO carbonyl 1 0 2 M 2-alkene 2 0 2 M 2-alkyne 2 0 2 M 3-allyl 3 -1 4 M 4-diene 4 0 4 5 -cyclo 5 -1 6 M pentadienyl 1 3.