DOCSLIB.ORG

Stress Tensor Eigenvector Following with Next-Generation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Stress Tensor Eigenvector Following with Next-Generation Heriot-Watt University Research Gateway Stress Tensor Eigenvector Following with Next-Generation Quantum Theory of Atoms in Molecules: Excited State Photochemical Reaction Path from Benzene to Benzvalene Citation for published version: Malcomson, T, Azizi, A, Momen, R, Xu, T, Kirk, SR, Paterson, MJ & Jenkins, S 2019, 'Stress Tensor Eigenvector Following with Next-Generation Quantum Theory of Atoms in Molecules: Excited State Photochemical Reaction Path from Benzene to Benzvalene', Journal of Physical Chemistry A, vol. 123, no. 38, pp. 8254-8264. https://doi.org/10.1021/acs.jpca.9b07519 Digital Object Identifier (DOI): 10.1021/acs.jpca.9b07519 Link: Link to publication record in Heriot-Watt Research Portal Document Version: Peer reviewed version Published In: Journal of Physical Chemistry A Publisher Rights Statement: This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry A, copyright © American Chemical Society after peer review and technical editing by the publisher. The final authenticated version is available online at: https://doi.org/10.1021/acs.jpca.9b07519 General rights Copyright for the publications made accessible via Heriot-Watt Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy Heriot-Watt University has made every reasonable effort to ensure that the content in Heriot-Watt Research Portal complies with UK legislation. If you believe that the public display of this file breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Download date: 23. Sep. 2021 Stress Tensor Eigenvector Following with Next-Generation Quantum Theory of Atoms in Molecules: Excited State Photochemical Reaction Path from Benzene to Benzvalene Thomas Malcomson1, Alireza Azizi2, Roya Momen2, Tianlv Xu2, Steven R. Kirk*2, Martin J. Paterson1, Samantha Jenkins*2 1Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK 2Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research and Key Laboratory of Resource National and Local Joint Engineering Laboratory for New Petro-chemical Materials and Fine Utilization of Resources, College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha, Hunan 410081, China email: [email protected] email: [email protected] In this investigation we considered both the scalar and 3-D vector-based measures of bonding using next generation quantum theory of atoms in molecules (QTAIM), constructed from the preferred direction of electronic charge density accumulation, to better understand the photo-chemical reaction associated with of the formation of benzvalene from benzene. The formation of benzvalene from benzene resulted in two additional C-C bonds forming compared with the benzene. The creation of the additional C-C bonds was explained in terms of an increasing the favorability of the reaction process by maximizing the bonding density. The topological instability of the benzvalene structure was determined using the scalar and vector-based measures to explain the short chemical half-life of benzvalene in terms of the competition between the formation of unstable new C-C bonding that also destabilizes nearest neighbor C-C bonds. The explosive character of benzvalene is indicated by the unusual tendency of the C-C bonds to rupture as easily as weak bonding. The topological instability of the short strong C-C bonds was explained by the existence of measures from conventional and next generation QTAIM that previously have only been observed in weak interactions such measures included twisted 3-D bonding descriptors. 1 Introduction While the 1971 synthesis of benzvalene, carried out by Katz,1 utilizing a ground state process by reacting cyclopentadiene with methyllithium and dichloromethane, this highly reactive olfin can also be produced in small quantities, alongside fulvene and Dewar benzene, through the excitation of benzene in the 245 nm range.2 Despite benzvalene possessing a chemical half-life of only 10 days3 before reverting back to benzene, benzvalene, along with fulvene and their associated excited state reactions are ideal to highlight the alterations in bonding structure induced through promotion of a molecule to an excited state4–6 The ability to understand this change in bonding, see Scheme 1, and the insights this provides about the potential energy surface surrounding the point of vertical excitation, could be a powerful tool throughout the chemical sciences. This understanding, however, is not easily discerned, even with modern advances in theoretical chemistry. S1 - vertical S - optimised 1 S1/S0 - conical intersection Benzvalene - S0 Benzene - S0 Scheme 1. The photochemical formulation of benzvalene from benzene. It is possible, however, to gleam some information on the interpretation of excited states through the manipulation of the CASSCF wavefunction to a VB like form, gaining local orbital occupancies (charge 7 densities) and spin-exchange coupling (Pij) values, see Table 1. For example, these electronic factors (successfully) predict that, upon optimisation in S1, the C-C bonds extend from the 1.40 Å (2.65 a.u), found in 7 S0, to 1.54 Å (2.91 a.u), see Scheme 2. The ability to analyze and visualize the continuous evolution of the chemical bonding can be highlighted in the excited state chemistry of calicene and sesquifulvalene, derivatives of fulvene, which has been previously studied.4–6 Despite the similarities of these compounds to fulvene, they each contain a significantly polarized central double bond, resulting in the most dominant resonance structure possessing a significantly polarized 2 bond. This highly polarized bond gives rise to significant charge transfer character in the lower excited state manifold8 that will have a strong effect on the excited state chemistry of these compounds, see the C4-C5 bond in Scheme 2. In this investigation therefore, we will present a new perspective of the chemical bonding of benzvalene using the 3-D, ‘next-generation’6 quantum theory of atoms in molecules (QTAIM) methodology.9,10 Next generation QTAIM has seen an increase in applications to excited states in recent years6 and is unique to theoretical chemistry due to being formulated as a directional 3-D vector based formulation as opposed to being comprised entirely of scalar measures that have recently been used for the prediction of stereoisomers.11 This three- stranded 3-D interpretation of the chemical bond is more complete than minimal definition of bonding (e3) the conventional QTAIM interpretation of a bond, provided by the bond-path (r) because it comprises all three of the {e1, e2, e3} eigenvectors. Within QTAIM the most preferred ‘easy’ direction e2 is determined on the basis of the ease of total electronic charge density ρ(rb) accumulation. Conversely, the least preferred directions were 12 found to be e1 for QTAIM and e2σ for the stress tensor. For the stress tensor, we have found that the e1σ eigenvector corresponds to the most preferred ‘easy’ direction on the basis of ease of compressibility. This finding was demonstrated using stress tensor trajectory formalism Tσ(s) in partnership with the potential energy surface to prove that the e2σ eigenvector was the least preferred direction of electronic charge density ρ(rb) accumulation and therefore that the e1σ eigenvector was the most preferred direction. Additional evidence for the most and least preferred directions for the stress tensor being defined by the e1σ and e2σ eigenvector was * * provided by the fact that the values for Hσ > Hσ and HσH > HσH consistent with previous findings from QTAIM that the preferred path has the longer associated eigenvector following path length. Previously, some of the current authors demonstrated that the stress tensor can be used within the QTAIM partitioning scheme by using next generation QTAIM.12 This analysis was undertaken using an adapted version of the recently introduced 3-D vector-based interpretation of the chemical bond B = {p,q,r} of the form Bσ = {ps,qs,r} to follow changes in the directional properties of the stress tensor that is robust to electronic excitations. We demonstrated that the construction of Bσ = {ps,qs,r} that used εσ ≤ 0 the most closely approximated the B = {p,q,r}. This is because the ‘easy’ direction for the stress tensor is determined by the most compressible λ1σ i.e. associated with the longer axis of the ellipse, whereas for QTAIM the ‘easy’ direction, (longer axis of the ellipse) is associated with the λ2 eigenvalue. 3 Scheme 2. The benzene S0, benzene S1vert and benzene S1opt (left), benzvalene S0/S1 ContInt (middle) and benzvalene S0 (right) molecular graphs, the bond-path (r) is indicated by the black lines with the undecorated green and red spheres representing the bond critical point (BCPs) and ring critical points (RCPs), respectively, with the white lines indicating the RCP-BCP paths. Recently,5 we provided a 3-D understanding of the bonding provided by using Lewis structures for the ground state S0 and first excited state S1 of fulvene. We discovered that the corresponding bond-path framework set B0,1 = {(p0,p1),(q0,q1),(r0,r1)}, was better approximated by the stress tensor formulation
Load more

Recommended publications
  • Triprismane (CH)6
    Triprismane (CH)6 Ein DaMocles Projekt von • Heiko Hofmann • Nina Hundertmark • Fatema Rad • Regina Sander Contents Introduction…………………………………………...page 1 Chemical and physical informations………………...page 2 Stability………………………………………………..page 3 Preparation……………………………………………page 4 - 6 Research and Development…………………………..page 7 - 8 References……………………………………………..page 9 Introduction Triprismane is the smallest and probably most famous member of a class of extraordinary and interesting polyhederanes, the [n]-prismanes. The smallest member of this hydrocarbon family was proposed by Ladenburg in 1869 as structure for benzene, and more than a century ago, the existence of triprimane became part of a discussion about cage compounds. Formally these cage compounds consist of an even number of methine units positioned at the corners of a regular prism. It's very high symmetry and their complex structure makes them not only difficult to preparate, but also highly strained. The conservation of orbital symmetry, publicised by Woodward and Hoffmann, is the most important facet about the durableness of triprismane and its thermodynamic stability. In 1965 Woodward won the nobel prize of chemistry for these rules. Seite 1 von 9 1.) Chemical and physical informations [3]-prismane [4]-prismane [5]-prismane [6]-prismane (ΔHf = 1338,9 kJ/mol) (ΔHf = 719,7 kJ/mol) (ΔHf = 602,5 kJ/mol) (ΔHf = 686,2 kJ/mol) ΔHf(Benzol) = 961,9 kJ/mol) These interpretations have been predicted by MM2 calculations as they are also used by programmes like ChemDraw. Empirical formula C6H6 CAS RN (Registry 650-42-0 N°) Name: IUPAC: teracylo[2.2.0.02,6.03,5]-hexane prismane, [3]-prismane, triprismane, ladenburg-Benzene.
    [Show full text]
  • MCSCF Study of S1 and S2 Photochemical Reactions of Benzene
    J. Am. Chem. Soc, 1993,11S, 673-682 673 for correcting for the change in charge distribution, and the present known experimental data. In calculating AGo(soln) for the neutral approach represents the most accurate method of obtaining an radicals from eq 8, the solution free energies are partitioned as estimate of Eo(S).The resulting values of Eo(s)were -1.19, -1.73, the sum of hydrogen-bonding (AGo(HB)) and non-hydrogen- -1.05, and -0.94 V for methylamine, ethylamine, dimethylamine, bonding (AGo(NHB)) terms, and the latter is treated as a constant and trimethylamine, respectively. Likewise, utilizing the values which depends on the number of CH2units in the molecule. It of AGO(,) derived above, one can estimate that Eo(I)has values was argued that the difference in AGo(soln) between a-carbon of about -1.5, -1.9, -1.5, and -1.4 V for the same amines, re- radicals, R'R2NCR3H', and the parent molecules, R1R?NCR3H2, spectively. The large negative values of Eo(I)confirm the strong is less than 2 kJ mol-' and can be neglected. For the charged reductive power of these R1R2NCR3H'radicals. Previous esti- species, the difference between trimethylaminium ((CH,),N'+) mates of Eo(])in aqueous solution have been in the region of -1.0 and trimethylammonium ((CH3),NH+) could be derived from V.@ Equilibrium measurements of these quantities in water will experimental estimates of AGO(so1n) of the two species. The be very difficult because of the transitory nature of both the increase in magnitude of the solution free energy of (CH3),N'+ radicals and the iminium products.
    [Show full text]
  • A Procedure for Computing Hydrocarbon Strain Energies Using Computational Group Equivalents, with Application to 66 Molecules
    Swarthmore College Works Chemistry & Biochemistry Faculty Works Chemistry & Biochemistry 2020 A Procedure For Computing Hydrocarbon Strain Energies Using Computational Group Equivalents, With Application To 66 Molecules Paul R. Rablen Swarthmore College, [email protected] Follow this and additional works at: https://works.swarthmore.edu/fac-chemistry Part of the Organic Chemistry Commons Let us know how access to these works benefits ouy Recommended Citation Paul R. Rablen. (2020). "A Procedure For Computing Hydrocarbon Strain Energies Using Computational Group Equivalents, With Application To 66 Molecules". Chemistry. Volume 2, Issue 2. 347-360. DOI: 10.3390/chemistry2020022 https://works.swarthmore.edu/fac-chemistry/252 This work is licensed under a Creative Commons Attribution 4.0 License. This work is brought to you for free by Swarthmore College Libraries' Works. It has been accepted for inclusion in Chemistry & Biochemistry Faculty Works by an authorized administrator of Works. For more information, please contact [email protected]. Article A Procedure for Computing Hydrocarbon Strain Energies Using Computational Group Equivalents, y with Application to 66 Molecules Paul R. Rablen Department of Chemistry and Biochemistry, Swarthmore College, Swarthmore, PA 19081, USA; [email protected] Dedication: This paper is dedicated to Professor Bernd Giese on the occasion of his 80th birthday. It was a y pleasure and an honor to work with you on the question of electron conduction in peptides a few years ago. Received: 4 April 2020; Accepted: 27 April 2020; Published: 30 April 2020 Abstract: A method is presented for the direct computation of hydrocarbon strain energies using computational group equivalents. Parameters are provided at several high levels of electronic structure theory: W1BD, G-4, CBS-APNO, CBS-QB3, and M062X/6-31+G(2df,p).
    [Show full text]
  • Symmetry 2010, 2, 1745-1762; Doi:10.3390/Sym2041745 OPEN ACCESS Symmetry ISSN 2073-8994
    Symmetry 2010, 2, 1745-1762; doi:10.3390/sym2041745 OPEN ACCESS symmetry ISSN 2073-8994 www.mdpi.com/journal/symmetry Review n– Polyanionic Hexagons: X6 (X = Si, Ge) Masae Takahashi Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan; E-Mail: [email protected]; Tel.: +81-22-795-4271; Fax: +81-22-795-7810 Received: 16 August 2010; in revised form: 7 September 2010 / Accepted: 27 September 2010 / Published: 30 September 2010 Abstract: The paper reviews the polyanionic hexagons of silicon and germanium, focusing on aromaticity. The chair-like structures of hexasila- and hexagermabenzene are similar to a nonaromatic cyclohexane (CH2)6 and dissimilar to aromatic D6h-symmetric benzene (CH)6, although silicon and germanium are in the same group of the periodic table as carbon. Recently, six-membered silicon and germanium rings with extra electrons instead of conventional substituents, such as alkyl, aryl, etc., were calculated by us to have D6h symmetry and to be aromatic. We summarize here our main findings and the background needed to reach them, and propose a synthetically accessible molecule. Keywords: aromaticity; density-functional-theory calculations; Wade’s rule; Zintl phases; silicon clusters; germanium clusters 1. Introduction This review treats the subject of hexagonal silicon and germanium clusters, paying attention to the two-dimensional aromaticity. The concept of aromaticity is one of the most fascinating problems in chemistry [1,2]. Benzene is the archetypical aromatic hexagon of carbon: it is a planar, cyclic, fully conjugated system that possesses delocalized electrons. The two-dimensional aromaticity of planar monocyclic systems is governed by Hückel’s 4N + 2 rule, where N is the number of electrons.
    [Show full text]
  • Durham E-Theses
    Durham E-Theses The photochemistry of highly uorinated pyridines Middleton, Roderick How to cite: Middleton, Roderick (1977) The photochemistry of highly uorinated pyridines, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/8331/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk UNIVERSITY OF DURHAM A THESIS entitled THE PHOTOCHEMISTRY OF HIGHLY FLUORINATED PYRIDINES Submitted by RODERICK MIDDLETON, B.Sc.(DUNELM) (Van Mlldert College) The copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. A candidate for the degree of Doctor of Philosophy . 1977 To My Mother MEMORANDUM This work was carried out at the University of Durham between October 1973 and October 1976. It is the original work of the author unless indicated by reference and has no been submitted for any other degree.
    [Show full text]
  • Reactions of Benzvalene with Tetracyanoethylene, 2,3-Dichloro-5, 6-Dicyano-P-Benzoquinone, Chlorosulfonyl Isocyanate, and Sulfur Dioxide
    J. Am. Chem. Soc. 1984, 106, 373-382 373 Reactions of Benzvalene with Tetracyanoethylene, 2,3-Dichloro-5, 6-dicyano-p-benzoquinone, Chlorosulfonyl Isocyanate, and Sulfur Dioxide. Evidence for Concerted 1,4-Cycloadditions to a Viny1cyclopropane System 1 Manfred Cbrist!, * Ericb Brunn, and Franz Lanzendorfer Contribution from the Inslitul fur Organische Chemie der Universiliit Wurzburg, Am Hubland, D-8700 Wurzburg, Federal Republic of Germany. Received June 17, 1983 Abstract: The reaction of benzvalene (4) with tetracyanoethylene (TCNE) affords a mixture of tetracyclo[3.3.0.02.4.0J·6]octane derivative 5, tricyclo[3.3.0.02•6]oct-7-ene derivative 6, and tricyclo[3.3.0.02•8]oct-6-ene derivative 7. By means of dideuterated benzvalene 4a and the solvent effect on the ratio of the products the mechanisms have been studied. Accordingly, the formation of the main products 5 and 6 involves zwitterionic intermediates, which arise from electrophilic attack of TCNE at the olefinic portion of 4. The third compound 7 is thought to be produced in a concerted 1,4-addition of TCNE to the vinylcyclopropane moiety of benzvalene (4). Treatment of 4 with 2,3-dichloro-5,6-dicyano-p-benzoquinone gives rise to a 1: 1 adduct, which is structurally analogous to TCNE adduct 7 and which is most probably formed in a one-step process as evidenced by the positions of the deuterons when 4a was utilized. In a reinvestigation of the reaction between chlorosulfonyl isocyanate and 4 the new compounds 18a, a 4-azatricyclo[3.3.0.02,8]oct-6-en-3-one derivative, and 19, an 8-azatetracyclo[ 4.2.0.02,4.0J·l]octan-7-one derivative, have been discovered in addition to the known products 2a and 3a.
    [Show full text]
  • Appendices Appendix A
    Appendices Appendix A Character Tables* of the More Common Symmetry Point Groups 1. Cyclic Groups A C2 E C2 A 1 1 z R z xz., y2, Z2, xy B 1 -1 x,y Rx' R y YZ, zx 2 C3 E C3 C3 W = exp (2ni/3) A 1 1 1 Z Rz .~ + y2, Z2 1 W w2 xz. - y2, xy, x,y E{ 1 w* W*2 } } Rx' Ry } yz, zx 3 C4 E C4 C2 c4 2 A 1 1 1 1 z R z x + I, Z2 B 1 -1 1 -1 r -I,xy 1 i -1 -i E { x,y Rx' Ry YZ,zx 1 -i -1 i } } } • Adapted from 1. Gutman and O.E. Polansky: Mathematical Concepts in Organic Chemistry. Springer, Berlin Heidelberg New York London Paris Tokyo 1986. Appendix 5, pp. 184-199 284 Appendix A. Character Tables ofthe More Common Symmetry Point Groups Cs E Cs Cs2 Cs3 Cs4 W = exp (271ij5) I A 1 1 1 1 1 - i R% xl +.1, Z2 1 W w2 w3 w4 { } x,y } yz,zx E1 1 w* W*2 W*3 W*4 }R", Ry 1 w2 w4 W w3 } xl -.I, xy E2 { 1 W*2 W*4 w* W*3 2 S C6 E C6 C3 C2 C3 C6 W = exp (271ij6) A 1 1 1 1 1 1 Z R% X2 +.I,z2 B 1 -1 1 -1 1 -1 1 W w1 -1 -w _w2 E1 { 1 w* W*2 -1 -w* _W*2 } x,y } R", Ry } YZ,zx 1 w2 w4 1 w2 w4 Ez { 1 W*2 W*4 1 W*2 W*4 } xl -.I, xy 2.
    [Show full text]
  • Third Millennium Ideal Gas and Condensed Phase Thermochemical Database for Combustion with Updates from Active Thermochemical Tables
    ANL-05/20 TAE 960 Third Millennium Ideal Gas and Condensed Phase Thermochemical Database for Combustion with Updates from Active Thermochemical Tables Alexander Burcat Faculty of Aerospace Engineering, Technion – Israel Institute of Technology Branko Ruscic Chemistry Division, Argonne National Laboratory September 2005 Argonne National Laboratory is managed by The University of Chicago for the U. S. Department of Energy About Argonne National Laboratory Argonne is managed by The University of Chicago for the U.S. Department of Energy under contract W-31-109-Eng-38. The Laboratory’s main facility is outside Chicago, at 9700 South Cass Avenue, Argonne, Illinois 60439. For information about Argonne and its pioneering science and technology programs, see www.anl.gov. Availability of This Report This report is available, at no cost, at http://www.osti.gov/bridge. It is also available on paper to U.S. Department of Energy and its contractors, for a processing fee, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831-0062 phone (865) 576-8401 fax (865) 576-5728 [email protected] Disclaimer This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor The University of Chicago, nor any of their employees or officers, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.
    [Show full text]
  • AND 7-PH!NTLCTCLOHIPTA-1,3,5-TRIIN!S FRON B!NZVAL!NI VIA 3,3A,,,5,5, &A­ 4 H!XAHYDRO·•,S,&-M!TH!NOCYCLOPBNTAPYRAZOLIS and TBTRACYCLO[ •
    Tetrahedron Vol. 45, No. 10, pp. 2905 to 2915, 1989 0040-4020/89 $3.00+.00 Printed in Great Britain. © 1989 Pergarnon Press plc 7-M!THYL- AND 7-PH!NTLCTCLOHIPTA-1,3,5-TRIIN!S FRON B!NZVAL!NI VIA 3,3a,,,5,5, &a­ 4 H!XAHYDRO·•,s,&-M!TH!NOCYCLOPBNTAPYRAZOLIS AND TBTRACYCLO[ •. 1. 0.01 ' • 0~' 1 lHIPTAHIS MANFRED CHRIStL••, ERICH BRUNN•, WOLFGANG R. ROTH~, AND HANS-WERHER LENNARTZ' Institut für Organische Chemie der Universität Würzburg•, Am Hubland, D-8700 Würzburg, Federal Republ ic of Germany Fakultät für Chemie der Universität Bochum~, Postfach 102148, D-4630 Bochum 1, Federal Republic of Germany (Received in Belgium 8 August 1988) Abstract: The addition of benzvalene < n to diazomethane, diazoethane, 2- diazopropane, phenyldiazomethane, and diphenyldiazomethane afforded the 1-pyrazolines 2a-; in good yields. By means of competition experiments, the relative reactivities of benzvalene 111 and norbornene with regard to diazomethane and 2-diazopropane have been determined. The fact that benz­ valene reacts about twice as fast as norbornene with both diazoalkanes cannot be rationalized on the basis of frontier orbital energies. On direct photolysis, the pyrazolines 2a-; were converted into the tetracy­ 2 4 3 clo[ 4. 1. 0. 0 • • 0 •., l heptanes 4a-; exclusi vely. These compounds gave the 1,3,5-cycloheptatrienes !5a,b,d,t,; in high yields on treatment with sil­ ver ions, thus providing better access to 7, 7-dimethyl-( Sdl and 7.7- diphenylcycloheptatriene C 5;1 than before. Su1•prisingly. the latter com­ pound is in equilibrium with a substantial Quantity of the norcaradiene form.
    [Show full text]
  • High-Temperature Isomerization of Benzenoid Polycyclic Aromatic Hydrocarbons
    Article Cite This: J. Org. Chem. 2018, 83, 3299−3304 pubs.acs.org/joc High-Temperature Isomerization of Benzenoid Polycyclic Aromatic Hydrocarbons. Analysis through the Bent Bond and Antiperiplanar Hypothesis Orbital Model Jean-Francoiş Parent and Pierre Deslongchamps* Departement́ de Chimie, Facultédes Sciences et de Genie,́ 1045 avenue de la medecine,́ UniversitéLaval, Quebec,́ QC G1 V 0A6, Canada *S Supporting Information ABSTRACT: L. T. Scott has discovered the 1,2-swapping of carbon and hydrogen atoms which is known to take place on benzenoid aromatics (up to ∼1000 °C range). For example, 13C-1-naphthalene is specifically converted to 13C-2-naphthalene, and there is evidence that this occurs through the formation of benzofulvene and a naphthalene−carbene intermediate. Application of the bent bond/antiperiplanar hypothesis leads to the postulate that higher in energy pyramidal singlet diradical intermediates can be used to propose a mechanism that rationalizes various atom rearrangements on benzenoid aromatics and related isomeric compounds. he specific 1,2-swapping of carbon and hydrogen atoms at was then postulated that the benzene isomerization must be T high temperature (≥1000 °C) on benzenoid aromatic taking place through the intermediate formation of the isomeric hydrocarbons was discovered by Scott and co-workers.1 One of benzvalene 7, a hypothesis supported by the thermal isomer- their initial investigations2 reported the selective thermal ization of d-1,d-2-benzvalene, which gave 1,2-deuteriobenzene isomerization of 13C-1-labeled naphthalene 1 to produce 13C- quantitatively.4 2 isomer 2 without any appearance of the 13C-8a isomer 3 It was thus believed that the carbon isomerization of (Figure 1).
    [Show full text]
  • A Procedure for Computing Hydrocarbon Strain Energies Using Computational Group Equivalents, † with Application to 66 Molecules
    Article A Procedure for Computing Hydrocarbon Strain Energies Using Computational Group Equivalents, y with Application to 66 Molecules Paul R. Rablen Department of Chemistry and Biochemistry, Swarthmore College, Swarthmore, PA 19081, USA; [email protected] Dedication: This paper is dedicated to Professor Bernd Giese on the occasion of his 80th birthday. It was a y pleasure and an honor to work with you on the question of electron conduction in peptides a few years ago. Received: 4 April 2020; Accepted: 27 April 2020; Published: 30 April 2020 Abstract: A method is presented for the direct computation of hydrocarbon strain energies using computational group equivalents. Parameters are provided at several high levels of electronic structure theory: W1BD, G-4, CBS-APNO, CBS-QB3, and M062X/6-31+G(2df,p). As an illustration of the procedure, strain energies are computed for 66 hydrocarbons, most of them highly strained. Keywords: strain; strain energy; group equivalents; strained hydrocarbons; calculated strain; quadricyclane; cubane; prismane; fenestranes; propellanes; spiroalkanes 1. Introduction The concept of strain has long held interest for organic chemists, going back all the way to Baeyer [1–5]. Strain refers to the amount by which the energy of a molecule exceeds that which one would expect if all bond lengths, bond angles, and dihedral angles could simultaneously hold their ideal values, and if no repulsive nonbonded interactions (steric repulsions) were present. As such, strain is generally assumed to be absent in molecules such as straight-chain alkanes in which the bond lengths, angles, and dihedral angles are not geometrically constrained, and in which the extended conformation avoids repulsive nonbonded interactions.
    [Show full text]
  • Nsu-Ehs-Chemical-Hygiene-Plan-2018
    ENVIRONMENTAL NOVA SOUTHEASTERN HEALTH AND SAFETY UNIVERSITY POLICY/PROCEDURE TITLE: POLICY/PROCEDURE Chemical Hygiene Plan NUMBER: 3 DOCUMENT HISTORY OWNER: Facilities Management/AHIS Date: 1 Sept 2011 APPROVED: NSU EHS Committee Date: 1 Sept 2013 IMPLEMENTED: Date: 1 Oct 2010 RETIRED: Date: Date: Revision No. Review / Changes Reviewer 7 August 2013 none 11 May 2018 1.0 Added EHS instead of EH&S and replaced MSDS with C. St Louis SDS CHEMICAL HYGIENE PLAN TABLE OF CONTENTS Section 1: Introduction Page 4 Section 2: Chemical Safety Guidelines Page 7 Section 3: Chemical Hygiene Responsibilities Page 9 Section 4: Exposure Assessments and Medical Surveillance Page 12 Section 5: Safety Data Sheets - SDS Page 16 Section 6: Chemical Labels Page 17 Section 7: Hazard Communication Page 18 Section 8: Permissible Exposure Limits Page 21 Section 9: Engineering Controls Page 22 Section 10: Classification of Hazardous Substances Page 32 Section 11: Chemical Handling Labeling and Storage Page 47 Section 12: Chemical Inventory Page 61 Section 13: Compressed Gas Safety Page 62 Section 14: Spill Response and Clean-up Guidelines Page 65 Section 15: Shipping / Receiving Chemicals Page 69 Section 16: Training Page 70 Section 17: Record Keeping Page 72 Section 18: Chemical Waste Disposal Page 73 Tables and Illustrations Table A: General Classes of Fires and Fire Extinguishers Page 23 Table B: Flammable and Combustible Liquids Class Characteristics Page 35 Table C: Solvent Substitutions Page 37 Table D: Common Cleaning Agents/Hazards/Precautions Page 45 Table
    [Show full text]