THE SYNTHESIS of STABLE Naphthoibjcyclobutadienes
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Cyclobutene Photochemistry. Steric Effects on the Photochemical Ring Opening of Alkylcyclobutenes
1688 J. Am. Chem. SOC.1995,117, 1688-1694 Cyclobutene Photochemistry. Steric Effects on the Photochemical Ring Opening of Alkylcyclobutenes William J. Leigh* and J. Albert0 Postigo Contribution ffom the Department of Chemistry, McMaster University, Hamilton, Ontario, Canada US4Ml Received August 19, 1994@ Abstract: Quantum yields for photochemical ring opening and cycloreversion in hydrocarbon solution have been determined for the direct photolysis (214 nm) of six 1,2-dimethylcyclobutenederivatives which contain methyl groups at C3 and C4 in numbers varying from zero to four. As the hydrogens on C& of the parent compound (1,2- dimethylcyclobutene)are replaced with increasing numbers of methyl groups, the total quantum yield for ring opening increases to a maximum of -0.3 and then decreases with further methyl substitution. The quantum yields for ring opening (&tal) of hexamethylcyclobutene and 1,2-dimethylcyclobuteneare nearly the same, and the lowest in the series. The maximum occurs with trans- 1,2,3,4-tetramethylcyclobutene;q5tod for the cis-isomer is significantly lower, but both yield an approximate 1:l mixture of formally allowed and forbidden diene isomers. A similar trend is observed in the relative quantum yields for ring opening and cycloreversion throughout the series. The results are interpreted in terms of a combination of bond strength and steric effects on the efficiency of the ring-opening process. Increasing methyl substitution causes an increase in @total through the first three members of the series owing to progressive weakening of the C3-C4 bond. Compounds containing cis-dimethyl substitution exhibit substantially reduced quantum yields for ring opening, relative to what would be expected based on bond strength effects alone. -
Exploring Antiaromaticity in Single-Molecule Junctions Formed
Nanoscale View Article Online PAPER View Journal | View Issue Exploring antiaromaticity in single-molecule junctions formed from biphenylene derivatives† Cite this: Nanoscale, 2019, 11, 20659 Markus Gantenbein,‡a Xiaohui Li, ‡b Sara Sangtarash, *‡c Jie Bai, b Gunnar Olsen, a Afaf Alqorashi,c Wenjing Hong, *b Colin J. Lambert *c and Martin R. Bryce *§a We report the synthesis of a series of oligophenylene-ethynylene (OPE) derivatives with biphenylene core units, designed to assess the effects of biphenylene antiaromaticity on charge transport in molecular junctions. Analogues with naphthalene, anthracene, fluorene and biphenyl cores are studied for compari- son. The molecules are terminated with pyridyl or methylthio units. Single-molecule conductance data were obtained using the mechanically controllable break junction (MCBJ) technique. It is found that when electrons pass from one electrode to the other via a phenylene ring, the electrical conductance is almost independent of the nature of the pendant π-systems attached to the phenylene ring and is rather insensi- Creative Commons Attribution 3.0 Unported Licence. tive to antiaromaticity. When electrons pass through the cyclobutadiene core of the biphenylene unit, transport is sensitive to the presence of the relatively weak single bonds connecting the two phenylene rings of biphenylene, which arise from partial antiaromaticity within the cyclobutadiene core. This leads to Received 25th June 2019, a negligible difference in the molecular conductance compared to the fluorene or biphenyl analogues Accepted 26th August 2019 which have standard single bonds. This ability to tune the conductance of molecular cores has no ana- DOI: 10.1039/c9nr05375a logue in junctions formed from artificial quantum dots and reflects the quantum nature of electron trans- rsc.li/nanoscale port in molecular junctions, even at room temperature. -
Cyclobutene Photochemistry. Identification of the Excited States Responsible for the Ring-Opening and Cycloreversion Reactions of Alkylcyclobutenes
J. Am. Chem. SOC.1991, 113,4993-4999 4993 Cyclobutene Photochemistry. Identification of the Excited States Responsible for the Ring-Opening and Cycloreversion Reactions of Alkylcyclobutenes W. J. Leigh,*?" K. Zheng,= N. Nguyen, N. H. Werstiuk, and J. Ma" Contribution from the Department of Chemistry, McMaster University, Hamilton, Ontario, Canada US4Ml. Received November 28, 1990. Revised Manuscript Received March 7, 1991 Abstract: Two substituted bicyclic cyclobutene derivatives-7-methyl- and 7-(trifluoromethyl)bicyclo[4.2.0]oct-7-enehave been prepared. Gas- and solution-phase UV absorption and He1 UV photoelectron spectra have been recorded for the two compounds as well as for the parent hydrocarbon bicyclo[4.2.0]oct-7-ene. The gas-phase spectra suggest that the a,R(3s) state is the lowest energy state in bicyclo[4.2.0]octene and the 7-methyl derivative but is raised to higher energies than the *,A* state in the 7-trifluoromethylderivative. Direct photolysis of the three compounds in hydrocarbon solution with monochromatic far-UV (1 93 and 214 nm) light leads to competitive ring opening to the corresponding cis,cis- and cis,trans-l,3-cyclooctadiene derivatives, as well as fragmentation to cyclohexene and alkyne in all three cases. Product quantum yields (193-nm excitation) have been measured for both substituted derivatives relative to those for the parent compound. The quantum yields of fragmentation products are highest for the methyl- and unsubstituted compounds, suggesting that these products arise from a Rydberg-like excited state. In contrast, ring opening is most efficient for the trifluoromethyl-substituted compound, although the diene distributions obtained from the reaction do not vary throughout the series. -
An Indicator of Triplet State Baird-Aromaticity
inorganics Article The Silacyclobutene Ring: An Indicator of Triplet State Baird-Aromaticity Rabia Ayub 1,2, Kjell Jorner 1,2 ID and Henrik Ottosson 1,2,* 1 Department of Chemistry—BMC, Uppsala University, Box 576, SE-751 23 Uppsala, Sweden; [email protected] (R.A.); [email protected] (K.J.) 2 Department of Chemistry-Ångström Laboratory Uppsala University, Box 523, SE-751 20 Uppsala, Sweden * Correspondence: [email protected]; Tel.: +46-18-4717476 Received: 23 October 2017; Accepted: 11 December 2017; Published: 15 December 2017 Abstract: Baird’s rule tells that the electron counts for aromaticity and antiaromaticity in the first ππ* triplet and singlet excited states (T1 and S1) are opposite to those in the ground state (S0). Our hypothesis is that a silacyclobutene (SCB) ring fused with a [4n]annulene will remain closed in the T1 state so as to retain T1 aromaticity of the annulene while it will ring-open when fused to a [4n + 2]annulene in order to alleviate T1 antiaromaticity. This feature should allow the SCB ring to function as an indicator for triplet state aromaticity. Quantum chemical calculations of energy and (anti)aromaticity changes along the reaction paths in the T1 state support our hypothesis. The SCB ring should indicate T1 aromaticity of [4n]annulenes by being photoinert except when fused to cyclobutadiene, where it ring-opens due to ring-strain relief. Keywords: Baird’s rule; computational chemistry; excited state aromaticity; Photostability 1. Introduction Baird showed in 1972 that the rules for aromaticity and antiaromaticity of annulenes are reversed in the lowest ππ* triplet state (T1) when compared to Hückel’s rule for the electronic ground state (S0)[1–3]. -
Exploitation of Baird Aromaticity and Clar's Rule for Tuning The
Article Exploitation of Baird Aromaticity and Clar’s Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons Felix Plasser Department of Chemistry, Loughborough University, Loughborough LE11 3TU, UK; [email protected] Abstract: Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four biphenylene-derived PAHs finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). The results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states. Keywords: aromaticity; antiaromaticity; chemical shift; hydrocarbons, benzene; p-conjugated systems Citation: Plasser, F. Exploitation of Baird Aromaticity and Clar’s Rule for 1. Introduction Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons. Polycyclic aromatic hydrocarbons (PAHs) are a fascinating class of molecules provid- Chemistry 2021, 3, 532–549. http:// ing versatile organic semi-conductors [1] for a variety of use cases such as photovoltaics [2] doi.org/10.3390/chemistry3020038 including singlet fission [3,4], charge transport [5], and field-effect transistors [6]. -
Cyclobutadiene
View metadata, citation and similar papers at core.ac.uk brought to you by CORE Published in "Angewandte Chemie International Edition 45(40): 6616 - 6619, 20 provided by RERO DOC Digital Library which should be cited to refer to this work. Cyclobutadiene: The Antiaromatic Paradigm? Thomas Bally* Keywords: In memory of Satoru Masamune antiaromaticity · cyclobutadiene · thermochemistry (1928–2003) There is probably no other single widely accepted (and hardly disputed) London proposed in 1937 a very appeal- molecule that has fascinated experimen- that benzene, with its six cyclically ing model that accounts for these effects tal and theoretical chemists so consis- delocalized p electrons, represents the in terms of ring currents that are in- tently over the past 40 years as has paradigm of aromaticity. In view of the duced by the external magnetic field in cyclobutadiene (CBD). On average, famous Hckel 4n/4n + 2 electron rule, the system of cyclically delocalized 16 publications which deal, in one form one is tempted to rush to the conclusion p electrons.[5] or another, with the parent compound that CBD, with its four cyclically delo- There has been a vigorous debate in p C4H4 and 40 which deal with cyclo- calized electrons, is therefore the recent years about whether and to what butdienes in general have appeared in paradigm of antiaromaticity. extent these ring currents contribute to every year of this time span, and there However, this conclusion is not as the deshielding or shielding of protons are probably many more on derivatives straightforward as it might seem, be- attached to aromatic or antiaromatic and metal complexes. -
Cheminformatics for Genome-Scale Metabolic Reconstructions
CHEMINFORMATICS FOR GENOME-SCALE METABOLIC RECONSTRUCTIONS John W. May European Molecular Biology Laboratory European Bioinformatics Institute University of Cambridge Homerton College A thesis submitted for the degree of Doctor of Philosophy June 2014 Declaration This thesis is the result of my own work and includes nothing which is the outcome of work done in collaboration except where specifically indicated in the text. This dissertation is not substantially the same as any I have submitted for a degree, diploma or other qualification at any other university, and no part has already been, or is currently being submitted for any degree, diploma or other qualification. This dissertation does not exceed the specified length limit of 60,000 words as defined by the Biology Degree Committee. This dissertation has been typeset using LATEX in 11 pt Palatino, one and half spaced, according to the specifications defined by the Board of Graduate Studies and the Biology Degree Committee. June 2014 John W. May to Róisín Acknowledgements This work was carried out in the Cheminformatics and Metabolism Group at the European Bioinformatics Institute (EMBL-EBI). The project was fund- ed by Unilever, the Biotechnology and Biological Sciences Research Coun- cil [BB/I532153/1], and the European Molecular Biology Laboratory. I would like to thank my supervisor, Christoph Steinbeck for his guidance and providing intellectual freedom. I am also thankful to each member of my thesis advisory committee: Gordon James, Julio Saez-Rodriguez, Kiran Patil, and Gos Micklem who gave their time, advice, and guidance. I am thankful to all members of the Cheminformatics and Metabolism Group. -
Aromatic Or Antiaromatic?
10322 J. Am. Chem. Soc. 2001, 123, 10322-10328 Butalene and Related Compounds: Aromatic or Antiaromatic? Philip M. Warner* and Graham B. Jones* Contribution from the Department of Chemistry, Northeastern UniVersity, Boston, Massachusetts 02115 ReceiVed May 7, 2001 Abstract: Density functional theory (DFT) has been used to study the first three members of the condensed cyclobutadienoid series, butalene (3), bicyclobutadienylene (12), and dicyclobutenobutalene (20). The first is planar and is judged “aromatic” by comparisons with suitable models using both energetic and magnetic criteria. The second is nonplanar, and not aromatic, but not so antiaromatic as cyclobutadiene (11). The third is slightly more antiaromatic and best viewed as a butalene fused to two cyclobutadiene rings; its properties are the sum of aromatic and antiaromatic components, like benzocyclobutadiene. Ring-opening transition states for both 3 and 12 have been located, and these are conrotatorily twisted. The ring-opening barrier for 12 is more than twice that for 3. Ring-opening of 20 involves ring inversion as the only barrier. Introduction The Bergman rearrangement of enediynes to p-benzynes (e.g., 1 to 2) continues to receive experimental and theoretical attention.1 The possibility that butalene (3), a “valence isomer” of 2, could have an independent existence was recognized over 25 years ago, when it was introduced as a theoretical species less stable than 2 and insulated from conversion to 2 by a 4.6 kcal/mol barrier (MINDO 3).2,3 The Breslow lab has reported experimental results implicating 3 as an intermediate.4,5 Briefly summarized, chloro-Dewar benzene 4 was treated with strong base to afford, in the presence of diphenylisobenzofuran, 10- 15% of amino-Dewar benzene adduct 6. -
Synthetic Approaches to Heterocyclic Bicyclo[2.1.0]Pentanes
SYNTHETIC APPROACHES TO HETEROCYCLIC BICYCLO[2.1.0]PENTANES Rabah N. Alsulami A THESIS Submitted to the Graduate College of Bowling Green State University in partial fulfillment of The requirements for the degree of MASTER OF SCIENCE August 2011 Committee: Thomas H. Kinstle (Advisor) Marshall Wilson Alexander N. Tarnovsky ABSTRACT Thomas H. Kinstle, Advisor Bicyclic systems such as bicyclo[2.1.0]pentanes and 5-oxabicyclo[2.1.0]pentanes are known to display a variety of unique chemical properties associated with their high strain energy. To the best of our knowledge, there were no reports regarding synthesis and investigation of 5- azabicyclo[2.1.0]pentanes. Therefore, the initial goal of this research was synthesis of 5-azabicyclo[2.1.0]pentane and investigation of its chemical properties. The cycloaddition reaction of azides (58, 59, 61) to olefins (54, 55) with further elimination of nitrogen was chosen as a synthetic method in order to obtain the compounds of interest. Starting olefins (3,3-dimethyl-1-cyclobutene-1-carboxylic acid (54) and methyl 3,3-dimethyl-1-cyclobutene-1-carboxylate (55) and azides phenyl azide (58), p- toluenesulfonyl azide (59), and picryl azide (61) were successfully synthesized and characterized by NMR spectroscopy and GCMS spectrometry. The addition reaction between azides and olefins was performed under various conditions, such as different solvents and temperature; however, according to NMR spectroscopy and GCMS spectrometry, olefins (54, 55) do not undergo cycloaddition reaction with azides (58, 59, 61). In order to investigate that behavior, cycloaddition reactions of more reactive olefins (66, 68) with azides (58, 59, 61) were performed under a variety of conditions. -
(12) United States Patent (10) Patent No.: US 7,968,215 B2 Begley Et Al
US007968215B2 (12) United States Patent (10) Patent No.: US 7,968,215 B2 Begley et al. (45) Date of Patent: Jun. 28, 2011 (54) OLED DEVICE WITH CYCLOBUTENE 4,539,507 A 9/1985 Vanslyke et al. ELECTRON INUECTION MATERALS 4,720,432 A 1/1988 Vanslyke et al. 4,768,292 A 9, 1988 Manzei et al. 4,769,292 A 9/1988 Tang et al. (75) Inventors: William J. Begley, Webster, NY (US); 4.885,211 A 12/1989 Tang et al. Natasha Andrievsky, Webster, NY (US) 4.885,221 A 12/1989 TSuneeda et al. 5,059,861 A 10, 1991 Littman et al. (73) Assignee: Global OLED Technology LLC, 5,059,862 A 10/1991 VanSlyke et al. Wilmington, DE (US) 5,061,569 A 10/1991 VanSlyke et al. 5,077,142 A 12/1991 Sakon et al. 5,121,029 A 6/1992 Hosokawa et al. (*) Notice: Subject to any disclaimer, the term of this 5,141,671 A 8/1992 Bryan et al. patent is extended or adjusted under 35 U.S.C. 154(b) by 287 days. (Continued) (21) Appl. No.: 12/330,547 FOREIGN PATENT DOCUMENTS EP 681019 11, 1995 (22) Filed: Dec. 9, 2008 (Continued) (65) Prior Publication Data OTHER PUBLICATIONS US 2010/01.41122 A1 Jun. 10, 2010 “Double Injection Electroluminescence in Anthracene”. RCA Review, 30, 322, (1969). (51) Int. C. HOIL 5/54 (2006.01) (Continued) CO7D 40/02 (2006.01) CO7D 47L/04 (2006.01) Primary Examiner —Dawn L. Garrett CO7D 403/02 (2006.01) (74) Attorney, Agent, or Firm — McKenna Long & Aldridge CO7D 213/6 (2006.01) LLP CO7D 40/4 (2006.01) CO7D 409/4 (2006.01) (57) ABSTRACT (52) U.S. -
Problems Discussed in the Videos
Problems discussed in the videos: Video (2) 44. The isolation of a new form of molecular carbon, C60, was reported in 1990. The substance has the shape of a soccer ball of carbon atoms and possesses the nickname “buckyball” (you don’t want to know the IUPAC name). Hydrogenation produces a hydrocarbon with the molecular formula C60H36. How many degrees of unsaturation are present in C60? In C60H36? Does the hydrogenation result place limits on the numbers of π bonds and rings in “buckyball”? Videos (2) – (3) 46. Write the structures of as many simple alkenes as you can that, upon catalytic hydrogenation with H2 over Pt, will give as the product (a) 2-methylbutane; (b) 2,3- dimethylbutane; (c) 3,3-dimethylpentane; (d) 1,1,4-trimethylcyclohexane. In each case in which you have identified more than one alkane as an answer, rank the alkenes in order of stability. Video (3) 64. What is the empirical formula? (Compound drawn on blackboard in video.) 65. What is the degree of unsaturation in cyclobutane? Video (4) 66. What is the IUPAC name? (Compound drawn on blackboard in video.) 28. The bicyclic alkene car-3-ene (drawn on blackboard in video), a constituent of turpentine, undergoes catalytic hydrogenation to give only one of the two possible stereoisomeric products, with the methyl group and the cyclopropane ring on the same face of the cyclohexane ring. Suggest an explanation for this stereochemical outcome. Videos (4) – (5) 29. Give the expected major product of catalytic hydrogenation of each of the following alkenes (drawn on blackboard in videos). -
Characterization and Catalytic Cracking of Tar Obtained in Coal
University of North Dakota UND Scholarly Commons Theses and Dissertations Theses, Dissertations, and Senior Projects January 2015 Characterization And Catalytic Cracking Of Tar Obtained In Coal / Biomass / Municipal Solid Waste Gasification: The seU Of Basic Mineral Catalysts And Miscibility, Properties, And Corrosivity Of Petroleum-Biofuel Oils And Blends For Application In Oil-Fired Power Stations Stacy Joan Bjorgaard Follow this and additional works at: https://commons.und.edu/theses Recommended Citation Bjorgaard, Stacy Joan, "Characterization And Catalytic Cracking Of Tar Obtained In Coal / Biomass / Municipal Solid Waste Gasification: The sU e Of Basic Mineral Catalysts And Miscibility, Properties, And Corrosivity Of Petroleum-Biofuel Oils And Blends For Application In Oil-Fired Power Stations" (2015). Theses and Dissertations. 1744. https://commons.und.edu/theses/1744 This Dissertation is brought to you for free and open access by the Theses, Dissertations, and Senior Projects at UND Scholarly Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of UND Scholarly Commons. For more information, please contact [email protected]. CHARACTERIZATION AND CATALYTIC CRACKING OF TAR OBTAINED IN COAL / BIOMASS / MUNICIPAL SOLID WASTE GASIFICATION: THE USE OF BASIC MINERAL CATALYSTS AND MISCIBILITY, PROPERTIES, AND CORROSIVITY OF PETROLEUM-BIOFUEL OILS AND BLENDS FOR APPLICATION IN OIL-FIRED POWER STATIONS by Stacy Joan Bjorgaard Bachelor of Science, University of North Dakota, 2010