DOCSLIB.ORG

Brief Review of Advances in Developments of Living Polymers

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Brief Review of Advances in Developments of Living Polymers Brief Review of Advances in Developments of Living Polymers by Michael Szwarc Hydrocarbon Research Institute, University of Southern California テトラヒドロフランのような極性非プロトン溶媒の中でナトリウムナフタリンのラジカルアニオンからス チレンモノマーへの1電子移動,それに続くスチレンのラジカルアニオンの2量化を開始反応とするリビン グアニオン重合が発見され,分子量のそろった単分散ポリスチレンやブロックコポリマーの合成はリビング アニオン重合によって可能となった.それから35年が過ぎたが,ビニルモノマーのカチオン重合法による リビングポリマー,あるいは金属ポルヒリンを用いた環状エーテル類のリビングポリマーの合成など,リビ ングポリマーの合成は大きく発展してきた.ここではリビングポリマーの開発の進歩について述べる. Polymerization is referred to as living when the free of homo polymers, were the only products. growing polymers retain their capacity of growth Thus, a novel method of synthesis of well character for a time sufficiently long to allow the operator to ized block-polymers was discovered. complete a contemplated task, i.e. when the reaction Synthetic advantages of living polymerization is propagated with virtual exclusion of termination and chain transfer. It is beneficial if all the polymer- Living polymerization provides synthetic polymer ic molecules start their growth simultaneously, chemists with powerfull tools for design polymer because then the resulting polymers are of uniform chains of requested specification, namely : size. (1) A control of the molecular mass of the for- The feasibility of such a polymerization was med polymers and a method of producing polymers demonstrated 35 years ago by simple and most of uniform size. convincing experiments' described here briefly. The (2) A new technique for preparing block- reactor, shown in Fig. 1, contained 60 ml of-3 .10' polymers of desired sequence of blocks of requested M THF solution of sodium naphthalenide (the initi- size and composition with exclusion of homo- ator) to which 10 gr. of styrene was added by polymers. crushing a breakseal. The polymerization ensued instantly and was over in seconds. The viscosity of the resulting solution was estimated by the time of fall, —5 s, of a plunger placed in a side tube filled with the polymer solution by tilting the reactor. After a while, additional 10 gr of styrene in 60 ml of THF was added. The subsequent polymerization was over again in seconds and the viscosity of the solution increased, as indicated by the increased of the time of fall of the plunger to 20 s. Since the concentration of the polymer did not change, this proved that the previously formed polymers retained their activity and grew longer on the addi- tion of the monomer. Repetition of these experi- ments using isoprene as a second monomer Equipment for demonstrating living character confirmed these conclusions since block-polymers, of polymerization. 798高 分 子40巻12月 号(1991年) (3) A method of attachment of desired func- butadiene-styrene-butadiene nor the di-block poly- tional groups to one or both ends of a polymer chain mers behave in this uncommon way. Similar prop- since the addition of a proper reagent easily con- erties are claimed for the cationically prepared verts the active end of a living polymer into a indene-iso-butene-indene ter-block polymers'. desired functional group''. Films of di-blocks of styrene and butadiene of a The control of molecular mass of the produced sufficiently high molecular mass have irridescent polymers is of obvious advantage. Living polymers colors', although the homo-polymers are colorless. can be "fed" by monomer until they attain the The color depends on the molecular mass of the desired size. Their number average momecular blocks and changes reversibly on touching the film, mass increases proportionally with conversion, pro- This phenomenon results from the incompatibility vided that all of them begin their growth simultane- of the blocks which, being bonded and unable to ously. This requirement is met when the rate of separate, form paralel lamellae 1000 A thick. initiation is faster of or equal to the rate of propaga- These act as an optical grating producing interfer- tion. Alternatively, polymers of uniform molecular ence colors. Such an effect is not shown by the size are formed by feeding with monomer the previ- blends of the homo-polymers since being not linked ously prepared "monomeric" or oligomeric living by chemical bond they can separate into large irreg- polymers. For example, cumyl potassium, a living ular domains. monomeric "poly-a-methylstyrene", grows to a liv- Another example revealing the effect of linking ing n-meric poly- a-methylstyrene on addition of incompatible blocks by chemical bond is shown by a-methylstyrene. The complex of 1-phenylethyl the di-block films casted from good solvents for one chloride with tin tetrachloride, CH3CH (Ph) Cl • block but poor for the other. The same styrene- SnC14 is a living monomeric "polystyrene"' yielding butadiene di-block forms a flexible film when casted on feeding with styrene a living n-meric--- from a solvent good for polybutadiene but bad for CH,CH (Ph) Cl SnCl., polystyrene. The metallated poly-styrene, whereas a glassy film is formed in the iso-butyric ester, (CH3) 2C (COOCE13) , Cat+, is a reverse case. In the former solvent polystyrene living monomeric "polymethyl methacrylate"4 form- blocks form granulae in a continuous matrix of the ing on the addition of the monomer a living-- flexible poly-butadiene, whereas polystyrene is the CH2C- (CH,) (COOCH3) , Cat+ polymethyl metha- continuous phase in the latter solvent. crylate. Nuyken5 used recently a stable solution of Many di-block polymers are effective emulsifying CH3CH (OR) I complexed with quaternary ammo- agents, especially when composed by hydrophilic nium salt to produce, by feeding it with monomer, a and hydrophobic blocks. Graft and comb-shape similarly complexed living iodide of polyvinyl ether, polymers are prepared by a modified living polymer etc. In all these cases the resulting polymers are of technique', and many of them are most useful as uniform size since all of them start their growth adhesive and elastomers. Similar procedures' lead simultaneously. to star-shape polymers valuable in control of Living polymerization is unique in allowing prep- rheological properties of lubricants and as an agent aration of block polymers of desired architecture, strengthening various polymeric materials. free of homo-polymers. The styrene-butadiene- Much interest is shown nowaday in well defined styrene is a commercial ter-block polymer produced macro-cyclic polymers prepared by linking the by living anionic technique having the interesting active ends of hi-functional living polymers with and useful thermo-plastic properties. It is moldable appropriate "linking" agents, e.g. di-carbanions of at higher temperatures but behaves as a tough living linear polystyrene converted into rings by a, cross-linked rubber at ambient conditions'. This w-dibromo-p-xylene or dimethyldichlorosilane'°. remarkable and reversible change of its properties is Their rheological behavior differs drastically from caused by the formation of rigid micro-spheres of that of linear polymers of the same degree of poly- glassy polystyrene on cooling the melt, and these act merization, for example their respective glass as giant cross-links. Significantly, neither the temperarature decreases with the degree of poly- 高分子40巻12月 号(1991年)799 merization" whereas it increases for linear poly- their rate of propagation is slown down on the mers. Significantly, it makes a difference whether addition of crown ethers or cryptates" that convert cyclic polymers of Mn-10,000 dalton are linked by the tight pairs into the loose ones. The retarding ortho rather than by para-dibromoxylene". effect of these powerful cation solvating agents Numerous functional polymers were prepared indicates the participation of push-pull effect, the from living anionic or cationic polymers. The prob- anion and cation cooperate in the monomer addition lems encountered in the preparation of functional process. polymers by anionic technique were discussed in a A more convincing evidence for the operation of recent review by Quirk". Novel kind of functional push-pull mechanism is provided by the reaction of polymers, referred to as macromers, were reported ethylene oxide with anions of substantially delocal- 11 years ago". Such polymers are terminated by ized charge. The undissociated ion-pairs of 9- units acting as monomers, e.g., methylfluorenyl" or fluoradenyl" cleave the oxir- ane faster than their free ions, the addition of ----CH=CHPh or --CH=C(CH3)C0 OCH3, cryptates retards the reaction, whereas the addition and could be copolymerized with small monomers of common cation salts, that convert the free anion yielding polymers with predetermined branches. into ion-pairs, accelerates its course. Polymers endowed with two functional end-groups, Living anionic polymerization of polymethyl known as telechelics, are most useful as chain exten- methacrylates is more complex, the active anions tion agents. For example, the diols formed by the form allylic-enolates solvated by penultimate poly- cationic ring-opening polymerization of cyclic mer units". Consequently, two centers may be ethers are used in preparation of urethane foams. involved in the propagation : the C- or the 0-. The Interesting amphilic gels were prepared by polymer- participation of 0- leads to some side reactions izing acrylic monomers with bi-macromers of which destroy the living character of this polymer- cationicaly produced living polyisobutene terminat- ization, especially in low polarity solvents. These ed on both ends by acrylic units. Such gels swell in undesired reactions are eliminated, or diminished, water and in organic solvents", and the character of by the
Load more

Recommended publications
  • The Progression of Chiral Anions from Concepts to Applications in Asymmetric Catalysis Robert J
    REVIEW ARTICLE PUBLISHED ONLINE: 24 JULY 2012 | DOI: 10.1038/NCHEM.1405 The progression of chiral anions from concepts to applications in asymmetric catalysis Robert J. Phipps, Gregory L. Hamilton and F. Dean Toste* Despite the tremendous advances of the past four decades, chemists are far from being able to use chiral catalysts to con- trol the stereoselectivity of any desired reaction. New concepts for the construction and mode of operation of chiral catalysts have the potential to open up previously inaccessible reaction space. The recognition and categorization of distinct approaches seems to play a role in triggering rapid exploration of new territory. This Review both reflects on the origins as well as details a selection of the latest examples of an area that has advanced considerably within the past five years or so: the use of chiral anions in asymmetric catalysis. Defining reactions as involving chiral anions is a difficult task owing to uncertainties over the exact catalytic mechanisms. Nevertheless, we attempt to provide an overview of the breadth of reactions that could reasonably fall under this umbrella. 9 ithin the broader field of science, organic chemistry is Of significantly greater acidity (pKa around 2–4) are chiral phos- often referred to as a mature field of study. In spite of this, phoric acids, commonly derived from BINOL (1,1′-bi-2-naphthol). Wnew avenues of inquiry seem to arise with relative fre- These catalysts have risen to prominence over the past decade quency. Perhaps we take it for granted that expansions of the field because their high acidity permits activation of a broad range of are sparked when one or two chemical laboratories uncover a new substrates3,10.
    [Show full text]
  • Organic Chemistry
    Wisebridge Learning Systems Organic Chemistry Reaction Mechanisms Pocket-Book WLS www.wisebridgelearning.com © 2006 J S Wetzel LEARNING STRATEGIES CONTENTS ● The key to building intuition is to develop the habit ALKANES of asking how each particular mechanism reflects Thermal Cracking - Pyrolysis . 1 general principles. Look for the concepts behind Combustion . 1 the chemistry to make organic chemistry more co- Free Radical Halogenation. 2 herent and rewarding. ALKENES Electrophilic Addition of HX to Alkenes . 3 ● Acid Catalyzed Hydration of Alkenes . 4 Exothermic reactions tend to follow pathways Electrophilic Addition of Halogens to Alkenes . 5 where like charges can separate or where un- Halohydrin Formation . 6 like charges can come together. When reading Free Radical Addition of HX to Alkenes . 7 organic chemistry mechanisms, keep the elec- Catalytic Hydrogenation of Alkenes. 8 tronegativities of the elements and their valence Oxidation of Alkenes to Vicinal Diols. 9 electron configurations always in your mind. Try Oxidative Cleavage of Alkenes . 10 to nterpret electron movement in terms of energy Ozonolysis of Alkenes . 10 Allylic Halogenation . 11 to make the reactions easier to understand and Oxymercuration-Demercuration . 13 remember. Hydroboration of Alkenes . 14 ALKYNES ● For MCAT preparation, pay special attention to Electrophilic Addition of HX to Alkynes . 15 Hydration of Alkynes. 15 reactions where the product hinges on regio- Free Radical Addition of HX to Alkynes . 16 and stereo-selectivity and reactions involving Electrophilic Halogenation of Alkynes. 16 resonant intermediates, which are special favor- Hydroboration of Alkynes . 17 ites of the test-writers. Catalytic Hydrogenation of Alkynes. 17 Reduction of Alkynes with Alkali Metal/Ammonia . 18 Formation and Use of Acetylide Anion Nucleophiles .
    [Show full text]
  • Aldehydes and Ketones
    12 Aldehydes and Ketones Ethanol from alcoholic beverages is first metabolized to acetaldehyde before being broken down further in the body. The reactivity of the carbonyl group of acetaldehyde allows it to bind to proteins in the body, the products of which lead to tissue damage and organ disease. Inset: A model of acetaldehyde. (Novastock/ Stock Connection/Glow Images) KEY QUESTIONS 12.1 What Are Aldehydes and Ketones? 12.8 What Is Keto–Enol Tautomerism? 12.2 How Are Aldehydes and Ketones Named? 12.9 How Are Aldehydes and Ketones Oxidized? 12.3 What Are the Physical Properties of Aldehydes 12.10 How Are Aldehydes and Ketones Reduced? and Ketones? 12.4 What Is the Most Common Reaction Theme of HOW TO Aldehydes and Ketones? 12.1 How to Predict the Product of a Grignard Reaction 12.5 What Are Grignard Reagents, and How Do They 12.2 How to Determine the Reactants Used to React with Aldehydes and Ketones? Synthesize a Hemiacetal or Acetal 12.6 What Are Hemiacetals and Acetals? 12.7 How Do Aldehydes and Ketones React with CHEMICAL CONNECTIONS Ammonia and Amines? 12A A Green Synthesis of Adipic Acid IN THIS AND several of the following chapters, we study the physical and chemical properties of compounds containing the carbonyl group, C O. Because this group is the functional group of aldehydes, ketones, and carboxylic acids and their derivatives, it is one of the most important functional groups in organic chemistry and in the chemistry of biological systems. The chemical properties of the carbonyl group are straightforward, and an understanding of its characteristic reaction themes leads very quickly to an understanding of a wide variety of organic reactions.
    [Show full text]
  • DNA Sequence Selectivity of Guanine-N7 Alkylation by Three Antitumor Chloroethylating Agents
    ICANCER RESEARCH 46, 1943-1947, April 19861 DNA Sequence Selectivity of Guanine-N7 Alkylation by Three Antitumor Chloroethylating Agents John A. Hartley,' Neil W. Gibson, Kurt W. Kohn, and William B. Mattes@ L.aboratory ofMolecular Pharmacology. Developmental Therapeutics Program, Division ofCancer Treatment, National Cancer institute, NiH, Bethesda, Maryland 20205 ABSTRACF (4). Both compounds are like C1EtNUs in that they produce The DNA sequenceselectivitiesof guanine-N7alkylation producedby delayed interstrand cross-linking in Mer (guanine-O@-alkyl three chloroethylating antitumor agents, I-(2-chloroethyl)-3-(cis-2-hy transferase deficient) human tumor cell lines, but not in Mer droxy)cyclohexyl-l-nitrosourea(cis-2-OH CCNU), 2-chloroethyl(meth cells, DNA-protein cross-linking in both cell types without ylsulfonyl)methanesulfonate,and 8-carhamoyl-3-(2-chloroethyl)imidazo delay, and selective killing of the Mer cells (5, 6). 15,l-dl-l,2,3,5-tetrazin-4(3H)-one (mitozolomide), were examined using We have recently investigated whether either of these agents a modificationof the Maxam and Gilbert sequencing technique. In a had a simpler alkylation chemistry than the C1EtNUs. One of region ofpBR322 DNA, 2-chloroethyl(methylsulfonyl)methanesulfonate the major alkylation routes of the C1EtNUs is the production produced approximately the same degree of alkylation at all guanines. of hydroxyethyl adducts in DNA (7). Such adducts are thought cis-2-OH CCNU, however,preferentiallyalkylated the middleguanines to have little importance in the expression ofantitumor activity in runs of three or more guanines the intensity of the reaction increased but may contribute to both the mutagenic and carcinogenic with the number of adjacent guanines in the DNA sequence.
    [Show full text]
  • Study These Chemical Functional Groups Until You Can Recognize Them
    Chemical Functional Groups: Study these chemical functional groups until you can recognize them. Alkane Carbonyl C O Alkene H Aldehyde C O Aromatic Ring Ketone C O H H Primary Alcohol Carboxylic OH OH Acid C H Secondary O Alcohol OH Carboxylate O C Tertiary O Alcohol OH O Ester Ether O O Primary Primary Ammonium Amine Ion NH3 NH2 Secondary Secondary Ammonium Amine Ion N N H H2 Tertiary Tertiary Ammonium Amine H N N Ion H Amide Imine N N O Thiol Thioester S SH O Sulfide S O Monophosphate P O O O O O Diphosphate P P O O O O O O O O Triphosphate P P P O O O O O O O 1. Draw the chemical structure of each amino acid for yourself. Identify every chemical functional group of each amino acid sidechain. ________________________________________________________________________________________________________ Hydrogen Bond Acceptors/Donors: “Polar molecules containing O-H and N-H bonds and the molecule HF have very large dipole moments and stronger than average dipole-dipole interactions. The hydrogen atoms in these molecules are bonded to small, highly electronegative atoms and have large partial positive charge. Therefore, the unequal distribution of the electrons in these molecules gives rise to large dipole moments. Because of its strength, the interaction between the partially positive hydrogen atom on one molecule and a partially negative O, N, or F atom with unshared pairs of electrons on an adjacent molecule merits special distinction: it is called a hydrogen bond” [Gilbert, Kirss, Foster, and Davies. Chemistry, 2nd Ed. 2009. pp. 473-474] 2.
    [Show full text]
  • CYCLIC OXONIUM IONS and RELATED STRUCTURES* Whose
    CYCLIC OXONIUM IONS AND RELATED STRUCTURES* BY ROBERT J. GARGIULO AND D. STANLEY TARBELL DEPARTMENT OF CHEMISTRY, VANDERBILT UNIVERSITY Communicated October 28, 1968 Abstract and Summary.-This paper describes the preparation by several methods of trialkyloxonium ions containing five-membered rings and the study of their structures by observing the nuclear magnetic resonance (NMR) spectra in several solvents. This provides independent evidence for these compounds, whose existence has been shown by kinetic, preparative, and stereochemical studies. The following SbCl6 oxonium salts have been prepared, isolated, and character- ized as crystalline solids: the 1,2,5-trimethyltetrahydrofuranium (Ha), the 1,2,2,5-tetramethyl (JIb), the trans-l-methylperhydrobenzofuranium (IVa), the trans-1,2-dimethyl (IVb), and the trans-1,2,2-trimethyl (IVc) compounds. The trifluoroacetate salts IIc, IId, IVd, and LWe have been made in acid solution, and all the salts II and IV have been characterized by their NMR spectra as cyclic- oxonium salts, with the charged 1-CH3 group downfield from an uncharged -OCH3. Spectra of all the SbCl6 salts in nitrobenzene solution are reported. Further evidence for the cyclic structure is given by the identification of 2,2,5- trimethyltetrahydrofuran (VIII) from the action of pyridine and lithium chloride on the 1,2,2,5-tetramethyltetrahydrofuranium salt JIb. Solvolysis of this salt by ethanol gave 2-ethoxy-2-methyl-5-methoxyhexane (VII) by attack at the tertiary carbon of the oxonium ion. The structure of VII was established by its synthesis and that of the other possible isomer. The trifluoroacetate oxonium ion (IVe) gave, after three days in 5 per cent sulfuric-trifluoroacetic acid, trans-2,2- dimethylperhydrobenzofuran and methyl trifluoroacetate.
    [Show full text]
  • Tricyclic Oxonium Tamed
    RESEARCH HIGHLIGHTS Nature Reviews Chemistry | https://doi.org/10.1038/s41570-019-0150-y | Published online 13 November 2019 NATURAL PRODUCT SYNTHESIS could only be characterized at low temperature. However, 1H and 13C NMR spectra are indicative of its Tricyclic oxonium tamed formation with large downfield shifts of the signals for the three Natural products or secondary formal positive charge on oxygen carbons adjacent to the oxygen and metabolites have hugely diverse (a trialkyloxonium ion) proposed for the protons attached to them. We decided structures. Simple-looking linear for other biosyntheses have proved In addition, a new cross-peak was to try to precursors can, via highly reactive far more elusive. observed in the 1H–13C correlation intermediates, fold up into a variety “The structures of a number spectrum, indicating the formation investigate of complex 3D structures. Writing of Laurencia natural products had of a new transannular bond. 1H and whether these in the Journal of the American originally been misassigned,” explains 13C chemical shifts calculated somewhat Chemical Society, Jonathan Burton Burton. “Our work with Rob Paton on using density functional theory also exotic looking and co-workers from the University calculating the NMR spectra for the favoured the assigned structures and of Oxford, in collaboration with proposed structures of these natural formation of the oxonium ions. species might Robert Paton at Colorado State products led us to earlier proposals of Four different oxonium ions really exist University, describe the synthesis and tricyclic oxonium species. We decided derived from the diastereomers characterization of tricyclic oxonium to try to investigate whether these of laurediol were prepared and intermediates and their conversion somewhat exotic looking species characterized — the formation of into ten different natural products might really exist.” one of these, from 3Z, S,S-laurediol originally isolated from algae of the In the proposed biosyntheses, is pictured.
    [Show full text]
  • Silane/Iodine-Based Cleavage of Esters and Ethers Under Neutral
    Proc. Nati. Acad. Scd. USA Vol. 75, No. 1, pp. 4-6, January 1978 Chemistry Silane/iodine-based cleavage of esters and ethers under neutral conditions* (ester cleavage/ether cleavage/dealkylation/iodotrimethylsilane/phenyltrimethylsilane-iodine) TSE-LOK HO AND GEORGE A. OLAH Institute of Hydrocarbon Chemistry, Department of Chemistry, University of Southern California, Los Angeles, California 90007 Contributed by George A. Olah, September 26, 1977 ABSTRACT New, efficient cleavage of carboxylic esters physical constants and spectral data that were in good agree- with iodotrimethylsilane or a mixture of phenyl imethylsilane ment with literature data or those of authentic samples. and iodine is described. Essentially neutral conditions can be maintained throughout the reactions. Ethers can be dealkylated Cleavage of Esters and Ethers by Phenyltrimethylsil- by the latter method in high yields. The mechanism of the ane/lodine. A mixture of the ester or ether (5 mmol), phen- cleavage reactions is considered to include six-membered ring yltrimethylsilane (1.0 g, 7.5 mmol), and iodine (1.91 g, 15 mg homopolar transition states. atom) was heated to 1100 for 2-6 hr (see Tables 3 and 4). It was then cooled and quenched with water, and the organic material The most commonly used and convenient method for pro- was extracted with benzene and washed with dilute sodium tecting carboxylic acids is esterification. In view of the frequent hydroxide. The aqueous phase was acidified, deiodinated with incompatibility, during ester hydrolysis, of alkaline conditions Na2S203, and extracted with benzene. Pure carboxylic acids with many sensitive functional groups, esters that permit and phenols were isolated from the benzene solution.
    [Show full text]
  • Aldehydes Can React with Alcohols to Form Hemiacetals
    340 14 . Nucleophilic substitution at C=O with loss of carbonyl oxygen You have, in fact, already met some reactions in which the carbonyl oxygen atom can be lost, but you probably didn’t notice at the time. The equilibrium between an aldehyde or ketone and its hydrate (p. 000) is one such reaction. O HO OH H2O + R1 R2 R1 R2 When the hydrate reverts to starting materials, either of its two oxygen atoms must leave: one OPh came from the water and one from the carbonyl group, so 50% of the time the oxygen atom that belonged to the carbonyl group will be lost. Usually, this is of no consequence, but it can be useful. O For example, in 1968 some chemists studying the reactions that take place inside mass spectrometers needed to label the carbonyl oxygen atom of this ketone with the isotope 18 O. 16 18 By stirring the ‘normal’ O compound with a large excess of isotopically labelled water, H 2 O, for a few hours in the presence of a drop of acid they were able to make the required labelled com- í In Chapter 13 we saw this way of pound. Without the acid catalyst, the exchange is very slow. Acid catalysis speeds the reaction up by making a reaction go faster by raising making the carbonyl group more electrophilic so that equilibrium is reached more quickly. The the energy of the starting material. We 18 also saw that the position of an equilibrium is controlled by mass action— O is in large excess.
    [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]
  • An Automated Ion Library Generator for Data Independent Acquisition Mass Spectrometry Analysis of Peptides and Glycopept
    bioRxiv preprint doi: https://doi.org/10.1101/696518; this version posted July 10, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. DIALib: an automated ion library generator for data independent acquisition mass spectrometry analysis of peptides and glycopeptides Toan K. Phung1*, Lucia F Zacchi2*, and Benjamin L. Schulz1,2¥ 1 School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Queensland, 4072, Australia. 2 ARC Training Centre for Biopharmaceutical Innovation, The University of Queensland, St. Lucia, QLD 4072, Australia. Running title: Automated construction of ion libraries for DIA ¥To whom correspondence should be addressed: Benjamin L. Schulz, School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Queensland, 4072, Australia. Tel.: +0061-7-336-54875; E-mail: [email protected] *These authors contributed equally to this work Keywords: SWATH-MS, peptide library, glycoproteomics, N-linked glycosylation, O-linked glycosylation bioRxiv preprint doi: https://doi.org/10.1101/696518; this version posted July 10, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. Abstract Data Independent Acquisition (DIA) Mass Spectrometry (MS) workflows allow unbiased measurement of all detectable peptides from complex proteomes, but require ion libraries for interrogation of peptides of interest.
    [Show full text]
  • Electrophilic Addition Reactions.Pdf
    Electrophilic Addition Reactions Electrophilic addition reactions are an important class of reactions that allow the interconversion of C=C and C≡C into a range of important functional groups. Conceptually, addition is the reverse of elimination What does the term "electrophilic addition" imply ? A electrophile, E+, is an electron poor species that will react with an electron rich species (the C=C) An addition implies that two systems combine to a single entity. Depending on the relative timing of these events, slightly different mechanisms are possible: • Reaction of the C=C with E+ to give a carbocation (or another cationic intermediate) that then reacts with a Nu- • Simultaneous formation of the two σ bonds The following pointers may aid your understanding of these reactions: • Recognise the electrophile present in the reagent combination • The electrophile adds first to the alkene, dictating the regioselectivity. • If the reaction proceeds via a planar carbocation, the reaction is not stereoselective • If the two new σ bonds form at the same time from the same species, then syn addition is observed • If the two new σ bonds form at different times from different species, then anti addition is observed Hydrogenation of Alkenes Reaction Type: Electrophilic Addition Summary • Alkenes can be reduced to alkanes with H2 in the presence of metal catalysts such as Pt, Pd, Ni or Rh. • The two new C-H σ bonds are formed simultaneously from H atoms absorbed into the metal surface. • The reaction is stereospecific giving only the syn addition product. • This reaction forms the basis of experimental "heats of hydrogenation" which can be used to establish the stability of isomeric alkenes.
    [Show full text]