DOCSLIB.ORG

Module No. 9: Homoaromaticity Subject Chemis

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Module No. 9: Homoaromaticity Subject Chemis Subject Chemistry Paper No. and Paper 1: ORGANIC CHEMISTRY- I (Nature of Title Bonding and Stereochemistry) Module No. and Module 9: Homoaromaticity Title Module Tag CHE_P1_M9 CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 9: Homoaromaticity Table of Content 1. Learning Outcomes 2. Introduction 3. Homoaromaticity 4. Evidence of Homoaromaticity 5. Criteria for homoaromaticity 6. Classification of homoaromatic compounds 7. Examples of homoaromatic compounds 7.1. Cationic homoaromatics 7.2. Neutral homoaromatics 7.2.1. Monohomoaromatics 7.2.2. Bishomoaromatics 7.2.3. 1,2-diboretane 7.2.4. Trishomoaromatics 7.3. Anionic homoaromatics 7.3.1. 1,2-diboretanide 7.3.2. Bis-diazene 8. Summary CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 9: Homoaromaticity 1. Learning Outcomes After studying this module, you shall be able to Understand the difference between aromaticity and homoaromaticity Understand about homoaromatic compounds Know the criteria for the compound to be homoaromatic Classify homoaromatic compounds Examples of homoaromatic compounds which includes cationic, neutral and anionic homoaromatics 2. Introduction As you are already aware of aromaticity which is most commonly defines molecule to be planar and have a complete delocalized system of (4n+2)π electrons. This complete cyclic delocalization of π electrons leads to an extra thermodynamic stability and explains many of the spectroscopic, magnetic, and chemical properties associated with aromatic compounds compared to a localized resonance form. It also accounts for the reactivity of aromatic compounds which differs significantly from alkenes (which tend to undergo addition reactions as compared to substitution reactions). Several molecules display aromatic character but do not strictly follow the definition mentioned above, leading to extensions to the definition of aromaticity for example, Möbius aromatics have (4n) π electrons yet they exhibit aromatic character. Spherically aromatic structures such as C are aromatic in spite of being non-planar. 60 Cyclopropane displays aromaticity in sigma orbitals rather than pi orbitals and inorganic pi complexes such as ferrocene exhibit aromaticity in three dimensions. Similarly, homoaromatic compounds also exhibits aromatic behaviour but in different manner which we will discuss in this module. CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 9: Homoaromaticity 3. Homoaromaticity In the previous module, we discussed about the compounds which contain alternate double and single bonds and follows the Hückel’s rule. But in 1959, Saul Winstein talked about a new class of aromatic molecules during his study of the “tris-homocyclopropenyl” cation. These molecules, were termed as a homoaromatic molecules which showed discontinuity in 3 the p orbital overlap due to the presence of a single sp hybridized atom, generally CH2 group, but larger alkyl residue or a heteroatom at one or several positions within the ring could also be present. So, we can say that “those compounds where the stable configuration systems with (4n + 2) e- can only be formed by bypassing one saturated sp3 hybridized carbon atom leads to homoaromaticity”. Such compounds are definitely less stable than the aromatic compounds (with complete delocalization of e-), as they show poor overlap of the p-orbitals. For example, Homotropylium ion (cyclooctatrienyl cation): This is formed when cyclooctatetraene is treated with H2SO4. The 6 e- can be assumed to be delocalized over seven carbon atoms, and the eighth saturated carbon atom undergo non-planarity. These homoaromatic compounds are generally exist as cationic and anionic species but some studies also give the evidences for the existence of neutral homoaromatic molecules, though these are less common. + The 'homotropylium' cation (C8H9 ) is perhaps the best studied example of a homoaromatic compound. CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 9: Homoaromaticity 4. Evidence of Homoaromaticity Winstein proposed the first homoaromatic compound i.e., tris-homocyclopropenyl cation (3) as shown. This evidence is collected from the acetolysis experiment of (1) in which its cis epimer reacts 35 times faster than the trans epimer. Evidences for homoaromatic structure was acquired from deuterium scrambling. It was found that 66% of deuterium was found on cyclopropane ring at position 1 and 5 and only 33% on carbinol carbon i.e., at position 3. This suggest that all the three positions 1,3 and 5 were equivalent. The structure (3) later on called as homoaromatic . After his discovery many cationic, neutral and anionic compounds have been suggested to show homoaromaticity. These compounds attain stability due to homoconjugation. Homoconjugation or in other words homoconjugative interactions accounts for the complete cyclic delocalization of 4n electrons and lowering of energy. But there are some other conditions which are responsible for the characteristic aromatic properties of these compounds. CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 9: Homoaromaticity 5. Criteria for Homoaromaticity To explain the characteristic aromatic properties of such compounds. We should first learn some of the conditions for the molecule, to show homoaromaticity are: 1) The molecule should possess one or more homoconjugative interactions (either through- bond or through-space) closing cyclic conjugation. 2) A closed cyclic system must show electron delocalization through. a) Effective overlap between the π -orbitals of the cyclic system. b) Bond orders and π -character indices should be close to that of an aromatic π -system c) Positive or negative charge should be delocalized throughout the cyclic system in case of charged molecules. d) There should be large degree of bond equalization resulting in difference of bond lengths from those of normal single or double bonds. 3) For either cyclopropyl or no-bond homoaromatic systems, the number of π –electrons participating in cyclic electron delocalization should be close to 4n +2. 4) Homoaromaticity should have resonance energy greater than 2 kcal mol-1 which leads to stabilization. 5) No-bond homoaromatic systems should possess exceptional magnetic properties that should lead to a) Significant equalization of 13C chemical shifts in the cyclic system. b) The magnetic susceptibility, χ, adopting a maximum value for an unconstrained homoaromatic system, indicating homoaromatic electron delocalization. c) A large chemical shift difference between the endo and exo oriented protons when the molecule possesses a CH2 group properly located above the ring. 6. Classification of homoaromatic compounds Homoaromatic compounds get stabilized due to some interactions, which results in delocalization. Therefore, depending on the type of interactions homoaromatics are classified into different categories: 1) No bond homoaromatic, where the cyclic delocalization is achieved through space. 2) Sigma bond homoaromatic, where the cyclic delocalization is achieved through bond interactions. CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 9: Homoaromaticity 3) Homoaromatics having transannular homoconjugative interactions, it perturbs the aromatic delocalization, for example the bridged annulenes 15(C1-C6) and 16 (C1-C5) also termed as homonaphthalene and homoannulene due to the transannular homoconjugation. No-bond and bond homoaromatics are related by rearrangement as illustrated in the valence tautomerism between 1,3,5-cycloheptatriene and nor-caradiene. Both of them are well set up for homoconjugation. In Winstein’s terminology, they are mono homoaromatic and termed as monohomobenzene as there is only one interruption to the direct aromatic conjugation of benzene. Multiple homoconjugative insertions into an aromatic may result in bis-, tris-, tetrahomoaromatics, etc. Now, let us work out on some examples to understand the homoaromaticity more clearly. 7. Examples of Homoaromatic compounds 7.1 Cationic Homoaromatics The cationic homoaromatic compounds are most studied species for homoaromaticity. For example, the homotropenylium cation. Many homoaromatic cationic compounds generally use a cyclopropenyl cation, a tropylium cation, or a cyclobutadiene di-cations as their basis since these compounds exhibit strong aromatic character. CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 9: Homoaromaticity Another well-established homoaromatic cation which shows strong homoaromaticity is norbornene-7-yl cation. An interesting example of pagodanes which is in dicationic form shows σ- bishomoaromaticity termed as 2 electron σ-bishomoaromatic systems. In these 4-center-2- electron systems the delocalization happens in the plane that is defined by the four carbon atoms (like σ-aromaticity is shown in cyclopropane which gains about 11.3 kcal mol−1 stability from the effect). The dications are formed either via oxidation of pagodane or via oxidation of the corresponding bis-seco-dodecahedradiene. But the reduction of the corresponding six electrons dianions was not possible so far. 7.2 Neutral Homoaromatic Compounds Some studies also account for less common neutral homoaromatic compounds. There are many classes which include in neutral homoaromatic compounds which are as follows: 7.2.1. Monohomoaromatics
Load more

Recommended publications
  • Topological Analysis of the Metal-Metal Bond: a Tutorial Review Christine Lepetit, Pierre Fau, Katia Fajerwerg, Myrtil L
    Topological analysis of the metal-metal bond: A tutorial review Christine Lepetit, Pierre Fau, Katia Fajerwerg, Myrtil L. Kahn, Bernard Silvi To cite this version: Christine Lepetit, Pierre Fau, Katia Fajerwerg, Myrtil L. Kahn, Bernard Silvi. Topological analysis of the metal-metal bond: A tutorial review. Coordination Chemistry Reviews, Elsevier, 2017, 345, pp.150-181. 10.1016/j.ccr.2017.04.009. hal-01540328 HAL Id: hal-01540328 https://hal.sorbonne-universite.fr/hal-01540328 Submitted on 16 Jun 2017 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. Topological analysis of the metal-metal bond: a tutorial review Christine Lepetita,b, Pierre Faua,b, Katia Fajerwerga,b, MyrtilL. Kahn a,b, Bernard Silvic,∗ aCNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France. bUniversité de Toulouse, UPS, INPT, F-31077 Toulouse Cedex 4, i France cSorbonne Universités, UPMC, Univ Paris 06, UMR 7616, Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005 Paris, France Abstract This contribution explains how the topological methods of analysis of the electron density and related functions such as the electron localization function (ELF) and the electron localizability indicator (ELI-D) enable the theoretical characterization of various metal-metal (M-M) bonds (multiple M-M bonds, dative M-M bonds).
    [Show full text]
  • Planar Cyclopenten‐4‐Yl Cations: Highly Delocalized Π Aromatics
    Angewandte Research Articles Chemie How to cite: Angew.Chem. Int. Ed. 2020, 59,18809–18815 Carbocations International Edition: doi.org/10.1002/anie.202009644 German Edition: doi.org/10.1002/ange.202009644 Planar Cyclopenten-4-yl Cations:Highly Delocalized p Aromatics Stabilized by Hyperconjugation Samuel Nees,Thomas Kupfer,Alexander Hofmann, and Holger Braunschweig* 1 B Abstract: Theoretical studies predicted the planar cyclopenten- being energetically favored by 18.8 kcalmolÀ over 1 (MP3/ 4-yl cation to be aclassical carbocation, and the highest-energy 6-31G**).[11–13] Thebishomoaromatic structure 1B itself is + 1 isomer of C5H7 .Hence,its existence has not been verified about 6–14 kcalmolÀ lower in energy (depending on the level experimentally so far.Wewere now able to isolate two stable of theory) than the classical planar structure 1C,making the derivatives of the cyclopenten-4-yl cation by reaction of bulky cyclopenten-4-yl cation (1C)the least favorable isomer.Early R alanes Cp AlBr2 with AlBr3.Elucidation of their (electronic) solvolysis studies are consistent with these findings,with structures by X-raydiffraction and quantum chemistry studies allylic 1A being the only observable isomer, notwithstanding revealed planar geometries and strong hyperconjugation the nature of the studied cyclopenteneprecursor.[14–18] Thus, interactions primarily from the C Al s bonds to the empty p attempts to generate isomer 1C,orits homoaromatic analog À orbital of the cationic sp2 carbon center.Aclose inspection of 1B,bysolvolysis of 4-Br/OTs-cyclopentene
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • Course No: CH15101CR Title: Inorganic Chemistry (03 Credits)
    Course No: CH15101CR Title: Inorganic Chemistry (03 Credits) Max. Marks: 75 Duration: 48 Contact hours (48L) End Term Exam: 60 Marks Continuous Assessment: 15 Marks Unit-I Stereochemistry and Bonding in the Compounds of Main Group Elements (16 Contact hours) Valence bond theory: Energy changes taking place during the formation of diatomic molecules; factors affecting the combined wave function. Bent's rule and energetics of hybridization. Resonance: Conditions, resonance energy and examples of some inorganic molecules/ions. Odd Electron Bonds: Types, properties and molecular orbital treatment. VSEPR: Recapitulation of assumptions, shapes of trigonal bypyramidal, octahedral and - 2- 2- pentagonal bipyramidal molecules / ions. (PCl5, VO3 , SF6, [SiF6] , [PbCl6] and IF7). Limitations of VSEPR theory. Molecular orbital theory: Salient features, variation of electron density with internuclear distance. Relative order of energy levels and molecular orbital diagrams of some heterodiatomic molecules /ions. Molecular orbital diagram of polyatomic molecules / ions. Delocalized Molecular Orbitals: Butadiene, cyclopentadiene and benzene. Detection of Hydrogen Bond: UV-VIS, IR and X-ray. Importance of hydrogen bonding. Unit-II Metal-Ligand Equilibria in Solution (16 Contact hours) Stepwise and overall formation constants. Inert & labile complexes. Stability of uncommon oxidation states. Metal Chelates: Characteristics, Chelate effect and the factors affecting stability of metal chelates. Determination of formation constants by pH- metry and spectrophotometry. Structural (ionic radii) and thermodynamic (hydration and lattice energies) effects of crystal field splitting. Jahn -Teller distortion, spectrochemical series and the nephleuxetic effect. Evidence of covalent bonding in transition metal complexes. Unit-III Pi-acid Metal Complexes (16 Contact hours) Transition Metal Carbonyls: Carbon monoxide as ligand, synthesis, reactions, structures and bonding of mono- and poly-nuclear carbonyls.
    [Show full text]
  • 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.
    [Show full text]
  • FAROOK COLLEGE (Autonomous)
    FAROOK COLLEGE (Autonomous) M.Sc. DEGREE PROGRAMME IN CHEMISTRY CHOICE BASED CREDIT AND SEMESTER SYSTEM-PG (FCCBCSSPG-2019) SCHEME AND SYLLABI 2019 ADMISSION ONWARDS 1 CERTIFICATE I hereby certify that the documents attached are the bona fide copies of the syllabus of M.Sc. Chemistry Programme to be effective from the academic year 2019-20 onwards. Date: Place: P R I N C I P A L 2 FAROOK COLLEGE (AUTONOMOUS) MSc. CHEMISTRY (CSS PATTERN) Regulations and Syllabus with effect from 2019 admission Pattern of the Programme a. The name of the programme shall be M.Sc. Chemistry under CSS pattern. b. The programme shall be offered in four semesters within a period of two academic years. c. Eligibility for admission will be as per the rules laid down by the College from time to time. d. Details of the courses offered for the programme are given in Table 1. The programme shall be conducted in accordance with the programme pattern, scheme of examination and syllabus prescribed. Of the 25 hours per week, 13 hours shall be allotted for theory and 12 hours for practical; 1 theory hour per week during even semesters shall be allotted for seminar. Theory Courses In the first three semesters, there will be four theory courses; and in the fourth semester, three theory courses. All the theory courses in the first and second semesters are core courses. In the third semester there will be three core theory courses and one elective theory course. College can choose any one of the elective courses given in Table 1.
    [Show full text]
  • 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.
    [Show full text]
  • PSO) - Course Outcome (CO)
    Bankim Sardar College A College with Potential for Excellence Department of Chemistry Programme Specific Outcome (PSO) - Course Outcome (CO) Programme Specific Outcome (PSO) : PSO 01. To understand basic facts and concepts in Chemistry while retaining the exciting aspects of Chemistry so as to develop interest in the study of chemistry as a discipline. PSO 02. To develop the ability to apply the principles of Chemistry. PSO 03. To appreciate the achievements in Chemistry and to know the role of Chemistry in nature and in society. PSO 04. To develop problem solving skills. PSO 05. To be familiarised with the emerging areas of Chemistry and their applications in various spheres of Chemical sciences and to apprise the students of its relevance in future studies. PSO 06. To develop skills in the proper handling of apparatus and chemicals. PSO 07. To be exposed to the different processes used in industries and their applications. Core Content of CU Syllabus Course Outcome Courses Semester 1 CCH01A INORGANIC CHEMISTRY-1 Students will be able to Extra nuclear Structure of atom CO 01. Develop an ability to use Quantum numbers and their significance, Schrödinger‟s wave conceptual and mathematical tools equation, significance of ψ and ψ2. Radial and angular wave functions to express and predict atomic and for hydrogen atom. Radial and angular distribution curves. Shapes of molecular behavior s, p, d and f orbitals. Pauli‟s Exclusion Principle, Hund‟s rules and CO 02. Discuss the Quantum mechanical multiplicity, Exchange energy, Aufbau principle and its limitations, concept of atom in the light of Ground state Term symbols of atoms and ions for atomic number upto modern chemistry 30.
    [Show full text]
  • Sc-Homoaromaticity
    This is a repository copy of Modern Valence-Bond Description of Homoaromaticity. White Rose Research Online URL for this paper: https://eprints.whiterose.ac.uk/106288/ Version: Accepted Version Article: Karadakov, Peter Borislavov orcid.org/0000-0002-2673-6804 and Cooper, David L. (2016) Modern Valence-Bond Description of Homoaromaticity. Journal of Physical Chemistry A. pp. 8769-8779. ISSN 1089-5639 https://doi.org/10.1021/acs.jpca.6b09426 Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. This is indicated by the licence information on the White Rose Research Online record for the item. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ Modern Valence-Bond Description of Homoaromaticity Peter B. Karadakov; and David L. Cooper; Department of Chemistry, University of York, Heslington, York, YO10 5DD, U.K. Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, U.K. Abstract Spin-coupled (SC) theory is used to obtain modern valence-bond (VB) descriptions of the electronic structures of local minimum and transition state geometries of three species that have been con- C sidered to exhibit homoconjugation and homoaromaticity: the homotropenylium ion, C8H9 , the C cycloheptatriene neutral ring, C7H8, and the 1,3-bishomotropenylium ion, C9H11.
    [Show full text]
  • Synthesis and Reactivity of Cyclopentadienyl Based Organometallic Compounds and Their Electrochemical and Biological Properties
    Synthesis and reactivity of cyclopentadienyl based organometallic compounds and their electrochemical and biological properties Sasmita Mishra Department of Chemistry National Institute of Technology Rourkela Synthesis and reactivity of cyclopentadienyl based organometallic compounds and their electrochemical and biological properties Dissertation submitted to the National Institute of Technology Rourkela In partial fulfillment of the requirements of the degree of Doctor of Philosophy in Chemistry by Sasmita Mishra (Roll Number: 511CY604) Under the supervision of Prof. Saurav Chatterjee February, 2017 Department of Chemistry National Institute of Technology Rourkela Department of Chemistry National Institute of Technology Rourkela Certificate of Examination Roll Number: 511CY604 Name: Sasmita Mishra Title of Dissertation: ''Synthesis and reactivity of cyclopentadienyl based organometallic compounds and their electrochemical and biological properties We the below signed, after checking the dissertation mentioned above and the official record book(s) of the student, hereby state our approval of the dissertation submitted in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Chemistry at National Institute of Technology Rourkela. We are satisfied with the volume, quality, correctness, and originality of the work. --------------------------- Prof. Saurav Chatterjee Principal Supervisor --------------------------- --------------------------- Prof. A. Sahoo. Prof. G. Hota Member (DSC) Member (DSC) ---------------------------
    [Show full text]
  • 20 Catalysis and Organometallic Chemistry of Monometallic Species
    20 Catalysis and organometallic chemistry of monometallic species Richard E. Douthwaite Department of Chemistry, University of York, Heslington, York, UK YO10 5DD Organometallic chemistry reported in 2003 again demonstrated the breadth of interest and application of this core chemical field. Significant discoveries and developments were reported particularly in the application and understanding of organometallic compounds in catalysis. Highlights include the continued develop- ment of catalytic reactions incorporating C–H activation processes, the demonstra- 1 tion of inverted electronic dependence in ligand substitution of palladium(0), and the synthesis of the first early-transition metal perfluoroalkyl complexes.2 1 Introduction A number of relevant reviews and collections of research papers spanning the transition metal series were published in 2003. The 50th anniversary of Ziegler catalysis was commemorated3,4 and a survey of metal mediated polymerisation using non-metallocene catalysts surveyed.5 Journal issues dedicated to selected topics included metal–carbon multiple bonds and related organometallics,6 developments in the reactivity of metal allyl and alkyl complexes,7 metal alkynyls,8 and carbon rich organometallic compounds including 1.9 Reviews of catalytic reactions using well-defined precatalyst complexes include alkene ring-closing and opening methathesis using molybdenum and tungsten imido DOI: 10.1039/b311797a Annu. Rep. Prog. Chem., Sect. A, 2004, 100, 385–406 385 alkylidene precatalysts,10 chiral organometallic half-sandwich
    [Show full text]