DOCSLIB.ORG

Process for Alkyne Hydrosilation Using Cycloalkene As Catalyst Modifier

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Process for Alkyne Hydrosilation Using Cycloalkene As Catalyst Modifier Europaisches Patentamt (19) European Patent Office Office europeen des brevets (11) EP 0 785 203 A1 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) IntCI.6: C07F7/14 23.07.1997 Bulletin 1997/30 (21) Application number: 97100533.5 (22) Date of filing : 1 5.01 .1 997 (84) Designated Contracting States: (72) Inventor: Roy, Aroop Kumar DE FRGBITNL Midland, Michigan 48642 (US) (30) Priority: 17.01.1996 US 583730 (74) Representative: Spott, Gottfried, Dr. et al Patentanwalte (71) Applicant: DOW CORNING CORPORATION Spott, Weinmiller & Partner Midland, Michigan 48686-0994 (US) Sendlinger-Tor-Platz 11 80336 Munchen (DE) (54) Process for alkyne hydrosilation using cycloalkene as catalyst modifier (57) A process is described for hydrosilating alkynes with organodihalosilanes and trihalosilanes in the presence of a platinum catalyst, selected from plati- num halides or the reaction product of platinum halides with organosilicon compounds having terminal aliphatic unsaturation. The process uses a cycloalkene compris- ing 6 to 20 carbon atoms as a catalyst modifier to reduce formation of the bis-silated adduct of the alkynes. < CO o CM LO CO o Q_ LU Printed by Rank Xerox (UK) Business Services 2.14.11/3.4 EP 0 785 203 A1 Description The present invention is a process for hydrosilating alkynes with organodihalosilanes or trihalosilanes in the pres- ence of a platinum catalyst, selected from platinum halides or the reaction product of platinum halides with organosili- 5 con compounds having terminal aliphatic unsaturation. This process uses a cycloalkene comprising 6 to 20 carbon atoms as a catalyst modifier to reduce formation of the bis-silated adduct of the alkynes. Virtually any compound which contains a =SiH group is reacted with compounds containing aliphatic unsaturation in the presence of a platinum compound, such as chloroplatinic acid, to effect a reaction typically referred to as hydrosi- lation or hydrosilylation. U.S. Patent 2,823,218 discusses such hydrosilation reactions in greater detail. 10 U.S. Patent 3,419,593 describes a group of catalysts that are the reaction product of chloroplatinic acid with orga- nosilicon compounds having terminal unsaturation that are particularly useful in hydrosilation processes. U.S. Patent 4,292,434 discloses a hydrosilation catalytic mixture obtained by dissolving a platinum halide in at least 20 parts by weight of olefin, for each part by weight of platinum halide, and subsequently heating and mixing the solu- tion obtained with from 0.5 to one mole of a primary or secondary amine for each gram atom of platinum. 15 A common problem associated with the hydrosilation of an alkyne with a hydridosilane, in the presence of a plati- num halide or platinum olefin complex as catalyst, is the formation of the bis-silated adduct of the alkyne as a by-prod- uct. Typically, such hydrosilation processes are run under high pressure to increase the concentration of alkyne in the reaction mixture, relative to the alkenyl substituted product, thereby minimizing the formation of the bis-silated adduct of the alkyne. However, alkynes such as acetylene are explosive at high pressures, thereby making those processes 20 dangerous. We have surprisingly found that in processes where an alkyne is silated with either a trihalosilane or orga- nodihalosilane in the presence of a platinum catalyst, selected from platinum halides or the reaction product of platinum halides with organosilicon compounds having terminal aliphatic unsaturation, the presence of a cycloalkene comprising 6 to 20 carbon atoms will reduce the amount formed of the bis-silated adduct of the alkyne. This reduction allows such processes to be run at near normal atmospheric pressure while still providing an acceptable ratio of alkenyl substituted 25 product to bis-silated adduct of the alkyne. The present invention is a process for hydrosilation of an alkyne. The process comprises contacting at a tempera- ture within a range of 40 to 150°C. an alkyne described by formula R1C=CH (1) where R1 is selected from hydrogen atom or alkyl groups comprising one to ten carbon atoms; with a hydridosilane described by formula R2nHSiX3.n (2) where R2 is selected from alkyl groups comprising one to 20 carbon atoms or aryl groups, each X is an independently 30 selected halogen atom and n has a value of zero or one; in the presence of a platinum catalyst selected from platinum halides or the reaction product of platinum halides with organosilicon compounds having terminal aliphatic unsaturation and a cycloalkene comprising 6 to 20 carbon atoms in an amount sufficient to reduce formation of a bis-hydrosilated adduct of the alkyne. The alkyne is contacted with the hydridosilane in standard low-pressure reactors suitable for reacting such com- 35 pounds. The pressure at which our process is conducted is not critical and is varied within a wide range. However, the present process is unexpectedly advantageous in that it is conducted at near normal atmospheric pressure while still providing an acceptable ratio of alkenyl-substituted product to bis-silated by-product. Therefore, it is preferred that the process is conducted at a pressure within a range of 10.1 to 303.9 kPa (0.1 to 3 atmospheres). More preferred is when the process is conducted at 101 .3 to 303.9 kPa (1 to 3 atmospheres). 40 The present process can be conducted in either a gas or liquid phase. However, it is preferred that the process is conducted in a liquid phase using a liquid hydrocarbon solvent in which the alkyne and hydridosilane are soluble. It is preferred that the liquid hydrocarbon solvent having a boiling point greater than the boiling point of the alkenyl substi- tuted product of our process to facilitate separation of the product from the solvent. The solvent is, for example, an aro- matic hydrocarbon such as xylene or a mixture of the isomers of xylene, toluene or benzene. A demonstration of such 45 a liquid phase process is provided in the examples herein. The present process is conducted at a temperature within a range of 40 to 1 50°C. A preferred temperature is 60 to 100°C. The optimal temperature for conducting our process will depend upon such factors as the alkyne and hydridosi- lane to be reacted. For example, when acetylene is reacted with methyldichlorosilane a preferred temperature for con- ducting the process is within a range of 70 to 80°C. so Alkynes useful in the present process are described by formula (1), where R1 is selected from hydrogen atoms or alkyl groups comprising one to ten carbon atoms. R1 is methyl, ethyl, propyl, tert-butyl and decyl. Preferred is when R1 is hydrogen atom, thereby making the alkyne acetylene. Hydridosilanes useful in our process are described by formula (2), where R2 is selected from alkyl groups compris- ing one to 20 carbon atoms or aryl groups, each X is an independently selected halogen atom and n has a value of zero 55 or one. R2 is, for example, alkyl groups such as methyl, ethyl, propyl and tert-butyl; halogen substituted alkyl groups such as chloromethyl or 3,3,3-trifluoropropyl; aryl groups such as phenyl, tolyl and xylyl; and halogen substituted aryl groups such as chlorophenyl. Preferred is when R2 is methyl. Also preferred is when X is a chlorine atom. The preferred hydridosilane is selected from trichlorosilane or methyldichlorosilane. The most preferred hydridosilane is methyldichlo- rosilane. 2 EP 0 785 203 A1 In the present process, it is preferred that the mole ratio of the alkyne to the hydridosilane fed to the process is within a range of 0.5:1 to 3:1 . Preferred is when the mole ratio of alkyne to hydridosilane is within a range of 1 :1 to 1 .3:1 . The present process is conducted in the presence of a platinum catalyst selected from platinum halides or the reac- tion product of platinum halides with organosilicon compounds having terminal aliphatic unsaturation. Platinum halides 5 useful in the present invention include platinum dichloride, platinum dibromide, platinum tetrachloride, dipotassium tet- rachloroplatinate (K2PtCI4) and chloroplatinic acid (H2PtCI6.6H20). The preferred platinum halide is chloroplatinic acid. Platinum catalysts useful in the present invention also include the reaction product of a platinum halide with an organo- silicon compound having terminal aliphatic unsaturation. Such catalysts are more fully described in U.S. Patent 3,419,593 which teaches platinum catalysts useful in the present process. A preferred catalyst for the present process 10 is the reaction product of a solution of chloroplatinic acid in 2-propanol with methylvinyldichlorosilane as shown in our examples herein. Other preferred catalysts are the reaction products of platinum dichloride or chloroplatinic acid with 1 ,3-divinyl-1 ,1 ,3,3- tetramethyldisiloxane. The concentrations of platinum catalyst used in the present process are varied within wide limits. In general, when our process is run as a batch process in the liquid phase the catalyst concentration in the liquid phase is that providing 15 one to 20,000 parts per million (ppm) of platinum. Preferred is 100 to 10,000 ppm of platinum in the liquid phase. The present process requires the presence of a cycloalkene comprising 6 to 20 carbon atoms in an amount suffi- cient to reduce the formation of a bis-hydrosilated adduct of the alkyne. Preferred are those cycloalkenes which do not undergo hydrosilation under our process conditions to create unwanted by-products. Preferred is when the cycloalkene comprises 7 to 1 0 carbon atoms. The cycloalkenes are, for example, cyclohexene, cycloheptene, cyclooctene, nor- 20 bornene and cyclodecene. The preferred cycloalkene is cyclooctene. In general, an amount of cycloalkene sufficient to reduce the formation of a bis-hydrosilated adduct of the alkyne is 200 to 5,000 moles of cycloalkene per each g • atom of platinum provided by the platinum catalyst to the process.
Load more

Recommended publications
  • 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].
    [Show full text]
  • Cycloalkanes, Cycloalkenes, and Cycloalkynes
    CYCLOALKANES, CYCLOALKENES, AND CYCLOALKYNES any important hydrocarbons, known as cycloalkanes, contain rings of carbon atoms linked together by single bonds. The simple cycloalkanes of formula (CH,), make up a particularly important homologous series in which the chemical properties change in a much more dramatic way with increasing n than do those of the acyclic hydrocarbons CH,(CH,),,-,H. The cyclo- alkanes with small rings (n = 3-6) are of special interest in exhibiting chemical properties intermediate between those of alkanes and alkenes. In this chapter we will show how this behavior can be explained in terms of angle strain and steric hindrance, concepts that have been introduced previously and will be used with increasing frequency as we proceed further. We also discuss the conformations of cycloalkanes, especially cyclo- hexane, in detail because of their importance to the chemistry of many kinds of naturally occurring organic compounds. Some attention also will be paid to polycyclic compounds, substances with more than one ring, and to cyclo- alkenes and cycloalkynes. 12-1 NOMENCLATURE AND PHYSICAL PROPERTIES OF CYCLOALKANES The IUPAC system for naming cycloalkanes and cycloalkenes was presented in some detail in Sections 3-2 and 3-3, and you may wish to review that ma- terial before proceeding further. Additional procedures are required for naming 446 12 Cycloalkanes, Cycloalkenes, and Cycloalkynes Table 12-1 Physical Properties of Alkanes and Cycloalkanes Density, Compounds Bp, "C Mp, "C diO,g ml-' propane cyclopropane butane cyclobutane pentane cyclopentane hexane cyclohexane heptane cycloheptane octane cyclooctane nonane cyclononane "At -40". bUnder pressure. polycyclic compounds, which have rings with common carbons, and these will be discussed later in this chapter.
    [Show full text]
  • Alkenes and Alkynes
    02/21/2019 CHAPTER FOUR Alkenes and Alkynes H N O I Cl C O C O Cl F3C C Cl C Cl Efavirenz Haloprogin (antiviral, AIDS therapeutic) (antifungal, antiseptic) Chapter 4 Table of Content * Unsaturated Hydrocarbons * Introduction and hybridization * Alkenes and Alkynes * Benzene and Phenyl groups * Structure of Alkenes, cis‐trans Isomerism * Nomenclature of Alkenes and Alkynes * Configuration cis/trans, and cis/trans Isomerism * Configuration E/Z * Physical Properties of Hydrocarbons * Acid‐Base Reactions of Hydrocarbons * pka and Hybridizations 1 02/21/2019 Unsaturated Hydrocarbons • Unsaturated Hydrocarbon: A hydrocarbon that contains one or more carbon‐carbon double or triple bonds or benzene‐like rings. – Alkene: contains a carbon‐carbon double bond and has the general formula CnH2n. – Alkyne: contains a carbon‐carbon triple bond and has the general formula CnH2n‐2. Introduction Alkenes ● Hydrocarbons containing C=C ● Old name: olefins • Steroids • Hormones • Biochemical regulators 2 02/21/2019 • Alkynes – Hydrocarbons containing C≡C – Common name: acetylenes Unsaturated Hydrocarbons • Arene: benzene and its derivatives (Ch 9) 3 02/21/2019 Benzene and Phenyl Groups • We do not study benzene and its derivatives until Chapter 9. – However, we show structural formulas of compounds containing a phenyl group before that time. – The phenyl group is not reactive under any of the conditions we describe in chapters 5‐8. Structure of Alkenes • The two carbon atoms of a double bond and the four atoms bonded to them lie in a plane, with bond angles of approximately 120°. 4 02/21/2019 Structure of Alkenes • Figure 4.1 According to the orbital overlap model, a double bond consists of one bond formed by overlap of sp2 hybrid orbitals and one bond formed by overlap of parallel 2p orbitals.
    [Show full text]
  • Stereospecific Fragmentations in the Mass Spectra of Stereoisomeric Isoindoloquinazolines
    Stereospecific Fragmentations in the Mass Spectra of Stereoisomeric Isoindoloquinazolines Vladimir V. Ovcharenko and Kalevi Pihlaja Structural Chemistry Group, Department of Chemistry, University of Turku, Turku, Finland Ge´za Sta´jer Institute of Pharmaceutical Chemistry, University of Szeged, Szeged, Hungary The mass spectrometric behavior of stereo- and regioisomeric, partially saturated isoindolo- quinazolines was studied by positive-ion electron ionization (EI) and fast-atom bombardment (FAB/LSIMS) mass spectrometry combined with collision-induced dissociation (CID). A highly stereospecific retro-Diels-Alder process was observed in the cyclohexene-fused isomers under the EI conditions, and a corresponding (although less specific) fragmentation was observed in their FAB spectra. In the absence of RDA fragmentations, regio- and stereoisomers of the cyclohexane-fused heterocycles could be distinguished based on their FAB/CID spectra. (J Am Soc Mass Spectrom 2003, 14, 1049–1056) © 2003 American Society for Mass Spectrometry arious condensed-skeleton heterocycles contain- behavior of these compounds under the EI and FAB ing up to three rings can be prepared starting conditions is reported in the present study. Vfrom stereoisomeric aminobicycloalkanecar- The choice of experimental methods was dictated by boxylic acids by applying a retro-Diels-Alder (RDA) the following considerations. Mass-spectrometric RDA decomposition as a part of the synthetic strategy. For fragmentations often proceed in a regio- or stereospe- instance, the reaction of 3-aminobicyclo[2.2.1]hept-5- cific manner [4, 5]. The structure-specificity of RDA ene-2-carboxylic acid with formylbenzoic acid followed phenomena have previously been studied by us in the by a mild thermolysis of the pentacyclic intermediate mass spectra of stereoisomeric polycondensed hetero- afforded the novel 1,3-oxazino[2,3-a]indole-2,6-dione cycles using various ionization methods, such as elec- [1].
    [Show full text]
  • Reactions of Alkenes and Alkynes
    05 Reactions of Alkenes and Alkynes Polyethylene is the most widely used plastic, making up items such as packing foam, plastic bottles, and plastic utensils (top: © Jon Larson/iStockphoto; middle: GNL Media/Digital Vision/Getty Images, Inc.; bottom: © Lakhesis/iStockphoto). Inset: A model of ethylene. KEY QUESTIONS 5.1 What Are the Characteristic Reactions of Alkenes? 5.8 How Can Alkynes Be Reduced to Alkenes and 5.2 What Is a Reaction Mechanism? Alkanes? 5.3 What Are the Mechanisms of Electrophilic Additions HOW TO to Alkenes? 5.1 How to Draw Mechanisms 5.4 What Are Carbocation Rearrangements? 5.5 What Is Hydroboration–Oxidation of an Alkene? CHEMICAL CONNECTIONS 5.6 How Can an Alkene Be Reduced to an Alkane? 5A Catalytic Cracking and the Importance of Alkenes 5.7 How Can an Acetylide Anion Be Used to Create a New Carbon–Carbon Bond? IN THIS CHAPTER, we begin our systematic study of organic reactions and their mecha- nisms. Reaction mechanisms are step-by-step descriptions of how reactions proceed and are one of the most important unifying concepts in organic chemistry. We use the reactions of alkenes as the vehicle to introduce this concept. 129 130 CHAPTER 5 Reactions of Alkenes and Alkynes 5.1 What Are the Characteristic Reactions of Alkenes? The most characteristic reaction of alkenes is addition to the carbon–carbon double bond in such a way that the pi bond is broken and, in its place, sigma bonds are formed to two new atoms or groups of atoms. Several examples of reactions at the carbon–carbon double bond are shown in Table 5.1, along with the descriptive name(s) associated with each.
    [Show full text]
  • II. Nomenclature Rules for Alkenes 1. the Parent Name Will Be the Longest
    1 Lecture 9 II. Nomenclature Rules For Alkenes 1. The parent name will be the longest carbon chain that contains both carbons of the double bond. Drop the -ane suffix of the alkane name and add the –ene suffix. Never name the double bond as a prefix. If a double bond is present, you have an alkene, not an alkane. alkane + -ene = alkene 2. Begin numbering the chain at the end nearest the double bond. Always number through the double bond and identify its position in the longest chain with the lower number. In the older IUPAC rules the number for the double bond was placed in front of the stem name with a hyphen. Under the newer rules, the number for the double bond is placed right in front of “ene”, with hyphens. We will use the newer rules for specifying the location of pi bonds. 1 2 3456 H3CCHCH CH 2 CH2 CH3 hex-2-ene (newer rules) 2-hexene (older rules) 3. Indicate the position of any substituent group by the number of the carbon atom in the parent (longest) chain to which it is attached. CH 1 2 345 3 H3CCHCHCHCH2 CH CH3 6 7 CH3 Numbering is determined by the double bond, not the branches, because the double bond has 5,6-dimethylhept-3-ene (newer rules) higher priority than any alkyl branch. 5,6-dimethyl-3-heptene (older rules) 4. Number cycloalkenes so that the double bond is 1,2 (number through the double bond). Number in the direction about the ring so that the lowest number is used at the first point of difference.
    [Show full text]
  • Free Radical Cyclisations
    rl zel-rf4 FREE RADICAL CYCLISATIONS A THESIS PRESENTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the UNIVERSITY OF ADELAIDE by T0NY LAWRENCE, B.Sc. (Hons. ) Departnrent of Organic Chemistry 1980 +: CONTENTS SUMMARY I STATEMENT II ACKNOhILEDGEMENTS III INTRODUI]TÏ()N 1 Background chemìstry 2 Outljne of the research project 21 Rates of cyclisation 27 Energies of activation 30 HEX.s.EN-1-YL RADICAL 32 2-METHYLHEX-5-EN-1-YL and 3-METHYLHEX-5-EN-1-YL RADICALS 43 2,z-DII4ETHYLHEX- s-EN- L-YL and 3,3-DIMETHYLHEX-s-EN-1-YL RADICALS 60 2,2,s.IRIMETHYLIIEX- 5- EN - 1.YL RADI CAL 78 2,2-DIIIETHYLPtNT-4-EN-1-YL and 3,3-DIMETHYLPENT-4-EN-1-YL RADICALS 97 OCT.7.ENE.2-YL RADICAL 108 4-METHYLHEX.5.EN.l-YL RADI CAL 118 HEX-s-YN-l-YL, HEPT-6-YN-l-YL and OCT-7-YN-l-YL RADICALS 131 5,6-EP0XYIjEXIìN- 1-YL RADI CAL r52 AFTËRl^IARD 159 EXPERIMENTAL SECI ION 163 Methods of reduction r64 Methods of analysis 17I Syntheti c rnethods 176 RE FERENCES 244 I SUMMARY The fol'ìowing free radicals were generated in solutíon by the reaction of tri-n-butyltin hydrÍde with the correspond'ing bromocompounds: Hex-5-en-1-yl, 2-Methyl hex-S-en-1-yl, 3-Methy'l hex-5-en-1-yl' 4-Methyl hex-5-en-1-yl, 2,2-Dimethy'l hex-5-en-1-yl, 3-3-Dimethyl hex-5-en-1-yl, 2,?-,5-Trimethyì hex-5-en-1-y'1, 2,2-Dimethyl pent-4-en-1-y1, 3,3-Dimethyl pent-4-en-1-yl, 1-Methylhept-6-en-1-y1, Hex-S-yn-1-y1, Hept-6-yn-1-yl' Oct-7-yn-l-yl, and 5,6-Epoxyhexan-1-yl .
    [Show full text]
  • Module 4 Alkenes and Alkynes Lecture 7 Alkenes 4.1 Introduction Hydrocarbons That Contain Carbon-Carbon Double Bond Are Called Alkenes (Also Called As Olefins)
    NPTEL – Biotechnology – Cell Biology Module 4 Alkenes and Alkynes Lecture 7 Alkenes 4.1 Introduction Hydrocarbons that contain carbon-carbon double bond are called Alkenes (also called as Olefins). Many alkenes are found in plant and animals. It has three sp2 orbitals that lie in a plane with angles of 120°. One of the carbon–carbon bonds in a double bond is σ-bond, formed by the overlap of a sp2 orbital of one carbon with a sp2 orbital of the other carbon. The second carbon–carbon bond in the double bond is formed from side-to-side overlap of the remaining p-orbitals of the carbons. These two p-orbitals must be parallel to each other to achieve maximum orbital-orbital overlap. Therefore, all six atoms of the double- bond system are in the same plane (Figure 1). Since there is maximum side-to-side overlap, rotation about a double bond does not occur. H H C C H H Figure 1 Each C-H σ-bond is formed by overlap of a sp2 hybrid orbital of carbon atom with the 1s orbital of a hydrogen atom. The C-H bond length in ethylene is slightly shorter than the C-H bond in ethane because the sp2 orbital in ethylene has more s character that attracts the electrons even more strongly. The C=C bond in ethylene is much shorter than the C-C bond in ethane, partly because the σ-bond of ethylene is formed from sp2 orbitals and partly because both σ- and π-bonds are attracting the atoms together (Figure 2).
    [Show full text]
  • Chem 150, Spring 2015 Unit 5
    Chem 150, Spring 2015 Unit 5 - Hydrocarbons Organic Chemistry and Hydrocarbons • Organic chemistry is the chemistry of carbon ✦ Carbon is unique among the elements in its ability to bond to itself and other elements in so many different ways. ✦ It was originally thought that only living systems could make organic molecules. ✦ Friedrich Wöhler demonstrated in 1828 that this was not the case. Chem 150, Unit 5: Hydrocarbons 2 Organic Chemistry and Hydrocarbons • Organic chemistry is the chemistry of carbon ✦ Carbon is unique among the elements in its ability to bond to itself and other elements in so many different ways. ✦ It was originally thought that only living systems could make organic molecules. ✦ Friedrich Wöhler demonstrated in 1828 that this was not the case. Chem 150, Unit 5: Hydrocarbons 2 Organic Chemistry and Hydrocarbons • Organic chemistry is the chemistry of carbon ✦ Carbon is unique among the elements in its ability to bond to itself and other elements in so many different ways. ✦ It was originally thought that only living systems could make organic molecules. ✦ Friedrich Wöhler demonstrated in 1828 that this was not the case. Chem 150, Unit 5: Hydrocarbons 2 9.1 The Special Properties of Carbon Chem 150, Unit 5: Hydrocarbons 3 Tetrahedral Geometry • When a carbon atom has four single bonds, the arrangement of atoms forms a tetrahedron. • The VSEPR model (Valence-shell electron pair repulsion model) predicts this geometry. Chem 150, Unit 5: Hydrocarbons 4 Lewis and Wedge-Dash Structures • Lewis structures are used even though they show bonds at right angles to one another. • To show the 3-dimensional structure chemists show perspective with wedges and dashed lines.
    [Show full text]
  • Alkenes and Alkynes
    04 Alkenes and Alkynes Carotene and carotene-like molecules are partnered with chlorophyll in nature to assist in the harvest of sunlight. In autumn, green chlorophyll molecules are destroyed and the yellows and reds of carotene and related molecules become visible. The red color of tomatoes comes from lycopene, a molecule closely related to carotene. See Problems 4.37 and 4.38. Inset: A model of b-carotene. (Charles D. Winters) KEY QUESTIONS 4.1 What Are the Structures and Shapes of Alkenes and HOW TO Alkynes? 4.1 How to Name an Alkene 4.2 How Do We Name Alkenes and Alkynes? CHEMICAL CONNECTIONS 4.3 What Are the Physical Properties of Alkenes and Alkynes? 4A Ethylene, a Plant Growth Regulator 4.4 Why Are 1-Alkynes (Terminal Alkynes) 4B Cis–Trans Isomerism in Vision Weak Acids? 4C Why Plants Emit Isoprene IN THIS CHAPTER, we begin our study of unsaturated hydrocarbons. An unsaturated hydro- carbon is a hydrocarbon that has fewer hydrogens bonded to carbon than an alkane has. There Alkene An unsaturated are three classes of unsaturated hydrocarbons: alkenes, alkynes, and arenes. Alkenes contain one hydrocarbon that contains or more carbon–carbon double bonds, and alkynes contain one or more carbon–carbon triple a carbon–carbon double bonds. Ethene (ethylene) is the simplest alkene, and ethyne (acetylene) is the simplest alkyne: bond. Alkyne An unsaturated H H hydrocarbon that contains a C C H C C H carbon–carbon triple bond. H H Ethene Ethyne (an alkene) (an alkyne) 108 Alkenes and Alkynes 109 ChemicalCheChmical i l ConnectionsConnect io ns 4A ETHYLENE, A PLANT GROWTH REGULATOR O Ethylene occurs only in trace amounts in nature.
    [Show full text]
  • Photocyclization of Arylethylenes: Mechanism and Scope of the Reactions
    Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 105, No. 6, December 1993, pp. 603-610. Printed in India. Photocyclization of arylethylenes: Mechanism and scope of the reactions R LAPOUYADE Photophysique et Photochimie Mol6culaire, UA du CNRS N ~ 348, Universit6 Bordeaux I, 33405 Talence, France Abstract. The photocyclization of three structural types of arylethylenes is systematically investigated in order to provide new pathways to regiospecifically substituted and/or partially hydrogenated polycyclic aromatic hydrocarbons. The scope of the photoformation of acenaphthenes from ~t-arylotefins,in amine solutions, is discussed: when the double bond is acyclic, only the naphthyl and the pyrenyl derivatives are photoreactive, but when the double bond is in a cycle, all the compounds which lead to the trans double bond photocyclize. The amine-mediated 1,3-H-shift, discovered with the preceding series, also occurs with 4a,4b-dihydrophenanthrene, formed by irradiation of 1,2-diarylethylenes, and leads to dihydrophenanthrenes. The photocyclization of 2-vinylbiphenyls is stereoselective from the singlet excited state but not from the triplet, where a fast equilibrium between E and Z configurations precedes the adiabatic cyclization. The radical cation of 2-vinylbiphenyls cyclizes to a phenanthrene radical cation which initiates a protic catalysis to the related fluorenes or, in presence of 2,6-di-t-butypyridine or water, leads stoichiometrically to phenanthrenes. Keywords. Arylethylenes; photocyclization; amine-mediated proton shift; polycyclic aromatic hydrocarbons. 1. Introduction Photocyclization of arylethylenes is the preferred method for synthesis of many different polycyclic aromatic hydrocarbons (PAH). There is an overwhelming amount of literature, recently surveyed (Laarhoven 1983; Mallory and Mallory 1984; Liu et al 1991), on the photocyclodehydrogenation of 1,2-diarylethylenes (stilbene-like) into angularly fused PAH (phenanthrene-like).
    [Show full text]
  • Klein 9-10 Alkenes Alkynes
    Grossman, CHE 230 Chapters 9–10. Additions across C=C π Bonds. We’ve learned a number of different substitution and elimination reactions of alkyl halides. We’ve learned that compounds with lone pairs are nucleophiles, and alkyl halides are electrophiles. Now we’re going to learn the reactions of a different class of nucleophiles: the C=C π bond in alkenes and alkynes. 10.1. Reactivity of Alkenes. The C=C π bond of an alkene is higher in energy than the C—H or C—C σ bond. As a result it can act as a nucleophile towards various electrophilic species. When a C=C π bond acts as a nucleophile, one of the C atoms takes the π electrons away from the other C and uses them to make a bond to the electrophile. The other C atom either becomes electron- deficient: The top C takes the pair of electrons from the π H H+ bond and uses it to make a σ bond to the H. The lower C has a pair of electrons taken away and becomes electron-deficient. or it gets a pair of electrons from the electrophile at the same time as the electrophile is getting a pair of electrons from the π bond: The top C takes the pair of electrons from the π bond and uses it to make a σ bond to one Br, Br Br displacing the other Br as a leaving group. Br+ Br– The electrophilic Br uses a lone pair to make a bond to the lower C to replace the π electrons that were taken away.
    [Show full text]