DOCSLIB.ORG

Reaction Mechanism-1 MODULE No. 7: Generation, Structure, Stability and Reactivity of Carbanions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Reaction Mechanism-1 MODULE No. 7: Generation, Structure, Stability and Reactivity of Carbanions Learn- More Weblinks . http://www.britannica.com/EBchecked/topic/94652/carbanion . http://www.youtube.com/watch?v=H86ZjDdPR-U . http://www.chem.wisc.edu/areas/reich/chem842/_chem842-01-intro%7B03%7D.htm . http://agrawalravin.blogspot.in/2013/03/carbanion.html . http://www.youtube.com/watch?v=fxXyuGLutgw . http://www.youtube.com/watch?v=l6LYVxx2u3s Suggested Readings . Reactive Intermediates in Organic Chemistry: Structure, Mechanism, and Reactions. By Maya Shankar Singh . Carbanion chemistry: structures and mechanisms. By E. Buncel, Julian Michael Dust . Carbanion chemistry. By Robert Brown Bates, Craig A. Ogle. Advanced Organic Chemistry: Reactions, Mechanisms And Structure, 4th Ed. By Jerry March CHEMISTRY PAPER No.5:Organic Chemistry-II (Reaction Mechanism-1 MODULE No. 7: Generation, structure, stability and reactivity of carbanions. Glossary A Aromaticity: It is a chemical property which provides extra stabilization by utilising the conjugated ring of unsaturated bonds, lone pairs, or empty orbitals. B Base: A base is a substance whose aqueous solution, is slippery, bitter, turns red litmus paper blue, produce hydroxide ions (OH-). C Chiral: A chiral molecule has a non-superposable mirror image and an asymmetric carbon atom. Conjugation: The overlap of one p-orbital with another across an intervening sigma bond. D Decarboxylation: A chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). D Dithiane: A heterocyclic compound with cyclohexane core structure where two methylene bridges are replaced by sulphur atoms (1,2-dithiane, 1,3-dithiane and 1,4-dithiane). E Electronegative: It is the tendency of an atom or a functional group to attract electrons (or electron density) towards itself. I Inversion: The inversion of a chiral center in a molecule in a chemical reaction. M Metallation: It is a chemical reaction which results in a metal atom being attached to an organic molecule. CHEMISTRY PAPER No.5:Organic Chemistry-II (Reaction Mechanism-1 MODULE No. 7: Generation, structure, stability and reactivity of carbanions. N Nucleophile: A chemical species that an donate electron pair to an electrophile to form a chemical bond. O Organometallic compounds: Organometallic compounds are those which contain chemical bonds between carbon and a metal. U Umpolung: The chemcal modification of a functional group with the reversal of polarity of that group. Y Ylide: A ylide or ylid is a neutral dipolar molecule containing forma negatively charged atom directly attached to a heteroatom with a formal positive charge (nitrogen, phosphorus or sulfur). Did You Know? Description Image The concept of Umpolung (German word for reversed polarity) was introduced by D. Seebach and E.J. Corey. Umpolung is the modification of a functional group to reverse the polarity of that group. Dieter Seebach is a German chemist. He is known for his synthesis of biopolymers and dendrimers, and for his contributions to stereochemistry. He became professor for organic chemistry at the University of Giessen. After six years he was appointed D. Seebach (1937) professor at the ETH Zurich. http://www.ae- info.org/ae/User/Seebach_Dieter Elias James Corey is an American organic chemist. He won the 1990 Nobel Prize in Chemistry for his development of the theory and methodology of organic synthesis. He is regarded as one of the greatest living chemists. E.J. Corey (1928) http://en.wikipedia.org/wiki/Elias_James_Co rey Source: http://en.wikipedia.org/wiki/Umpolung CHEMISTRY PAPER No.5:Organic Chemistry-II (Reaction Mechanism-1 MODULE No. 7: Generation, structure, stability and reactivity of carbanions. Description Image Georg Wittig was a German chemist. He gave a method for synthesis of alkenes from aldehydes and ketones using compounds called phosphonium ylides in the Wittig reaction. He shared the Nobel Prize in Chemistry with Herbert C. Brown in 1979. Georg Wittig (1897–1987) Source: http://en.wikipedia.org/wiki/Georg_Wittig Source: http://en.wikipedia.org/wiki/Georg_Wittig Description Image Erich Armand Arthur Joseph Hückel was a German physicist and physical chemist. He is known for the Debye–Hückel theory, the Hückel method of approximate molecular orbital (MO) calculations on π electron systems and proposing Huckel rule for aromaticity. Erich Armand Arthur Joseph Hückel (1896-1980) Source: http://en.wikipedia.org/wiki/Erich_H%C3%BCckel Description Image Rainer Ludwig Claisen was a German chemist. He is known for ondensations of carbonyls and sigmatropic rearrangements. In 1874 he started his academic career at University of Bonn. CHEMISTRY PAPER No.5:Organic Chemistry-II (Reaction Mechanism-1 MODULE No. 7: Generation, structure, stability and reactivity of carbanions. Rainer Ludwig Claisen (1851– 1930) Source: http://en.wikipedia.org/wiki/Rainer_Ludwig_Claisen CHEMISTRY PAPER No.5:Organic Chemistry-II (Reaction Mechanism-1 MODULE No. 7: Generation, structure, stability and reactivity of carbanions. .
Load more

Recommended publications
  • UMPOLUNG in REACTIONS CATALYZED by THIAMINE PYROPHOSPHATE DEPENDENT ENZYMES Umpolung En Reacciones Catalizadas Por Enzimas Dependientes De Pirofosfato De Tiamina
    Ciencia, Ambiente y Clima, Vol. 2, No. 2, julio-diciembre, 2019 • ISSN (impreso): 2636-2317 • ISSN (en línea): 2636-2333 DOI: https://doi.org/10.22206/cac.2019.v2i2.pp27-42 UMPOLUNG IN REACTIONS CATALYZED BY THIAMINE PYROPHOSPHATE DEPENDENT ENZYMES Umpolung en reacciones catalizadas por enzimas dependientes de pirofosfato de tiamina Carlos José Boluda Emily Soto Instituto Tecnológico de Santo Domingo (INTEC), Instituto Tecnológico de Santo Domingo (INTEC), Área de Ciencias Básicas y Ambientales, Av. de Los Área de Ciencias Básicas y Ambientales Próceres 49, Santo Domingo, República Dominicana Correo-e: [email protected] *Corresponding author: Carlos J. Boluda Darah de la Cruz Correo-e: [email protected] Instituto Tecnológico de Santo Domingo (INTEC), Carolina Juncá Área de Ciencias Básicas y Ambientales Instituto Tecnológico de Santo Domingo (INTEC), Correo-e: [email protected] Área de Ciencias Básicas y Ambientales Anny Peña Correo-e: [email protected] Instituto Tecnológico de Santo Domingo (INTEC), Área de Ciencias Básicas y Ambientales Correo-e: [email protected] Recibido: 25/9/2019 • Aprobado: 19/10/2019 Cómo citar: Boluda, C. J., Juncá, C., Soto, E., de la Cruz, D., & Peña, A. (2019). Umpolung in reactions catalyzed by thiamine pyrophos- phate dependent enzymes. Ciencia, Ambiente Y Clima, 2(2), 27-42. Doi: https://doi.org/10.22206/cac.2019.v2i2.pp27-42 Abstract Resumen The temporal exchange of the electrophilic/nucleophilic El intercambio temporal del carácter electrofílico/nucleofí- character of an atom by chemical manipulation is known lico de un átomo mediante manipulación química, es cono- in organic chemistry as umpolung. This inversion of polarity cido con el vocablo alemán de umpolung.
    [Show full text]
  • Products from Reactions of Carbon Nucleophiles and Carbon
    14C synthesis strategies, Chem 315/316 / Beauchamp 1 Products from reactions of carbon nucleophiles and carbon electrophiles used in the 14C Game and our course: Carbon and hydrogen nucleophiles Ph R Ph Al H N R Li R (MgBr) P Li AlH R Cu Li Na CN RCC Na Ph 4 Li Carbon 2 H C R organolithium organolithium cyanide acetylides 2 ylid Na BH4 diisobutylaluminium lithium diisopropy- electrophiles cuprates (LAH) o reagents reagents Wittig reagents hydride (DIBAH) amide (LDA), -78 C H C Br 3 not useful not useful 2 RX coupling nitrilesalkynes not useful alkyls alkyls not useful methyl RX reaction R Br not useful not useful 2 RX coupling nitriles alkynes not useful alkyls alkyls not useful primary RX reaction R 2 RX coupling nitriles alkyls not useful E2 not useful alkyls not useful not useful reaction R Br secondary RX O 1o ROH 1o ROH 1o ROH 1o ROH not useful 1o ROH o not useful not useful 1o ROH 1 ROH ethylene oxide nitriles alkynes O o o o o o o 2 ROH 2 ROH 2 ROH 2 ROH 2o ROH 2 ROH 2 ROH not useful not useful E2, make nitriles alkynes allylic alcohols propylene oxide O o 3 ROH 3o ROH o 3o ROH o not useful o 3o ROH not useful E2, make 3 ROH 3 ROH 3 ROH allylic alcohols nitriles alkynes isobutylene oxide O o o specific methanol methanol C 1 ROH 1 ROH not used cyanohydrin 1o ROH not useful not useful in our course alkenes H H alkynes methanal O specific o enolate o o cyanohydrin o 1 ROH o C 2 ROH 2 ROH not useful 2 ROH alkenes 1 ROH not useful chemistry R H alkynes simple aldehydes O cyanohydrin o unless specific o enolate C 3 ROH 3o ROH o 2o ROH
    [Show full text]
  • Chapter 7, Haloalkanes, Properties and Substitution Reactions of Haloalkanes Table of Contents 1
    Chapter 7, Haloalkanes, Properties and Substitution Reactions of Haloalkanes Table of Contents 1. Alkyl Halides (Haloalkane) 2. Nucleophilic Substitution Reactions (SNX, X=1 or 2) 3. Nucleophiles (Acid-Base Chemistry, pka) 4. Leaving Groups (Acid-Base Chemistry, pka) 5. Kinetics of a Nucleophilic Substitution Reaction: An SN2 Reaction 6. A Mechanism for the SN2 Reaction 7. The Stereochemistry of SN2 Reactions 8. A Mechanism for the SN1 Reaction 9. Carbocations, SN1, E1 10. Stereochemistry of SN1 Reactions 11. Factors Affecting the Rates of SN1 and SN2 Reactions 12. --Eliminations, E1 and E2 13. E2 and E1 mechanisms and product predictions In this chapter we will consider: What groups can be replaced (i.e., substituted) or eliminated The various mechanisms by which such processes occur The conditions that can promote such reactions Alkyl Halides (Haloalkane) An alkyl halide has a halogen atom bonded to an sp3-hybridized (tetrahedral) carbon atom The carbon–chlorine and carbon– bromine bonds are polarized because the halogen is more electronegative than carbon The carbon-iodine bond do not have a per- manent dipole, the bond is easily polarizable Iodine is a good leaving group due to its polarizability, i.e. its ability to stabilize a charge due to its large atomic size Generally, a carbon-halogen bond is polar with a partial positive () charge on the carbon and partial negative () charge on the halogen C X X = Cl, Br, I Different Types of Organic Halides Alkyl halides (haloalkanes) sp3-hybridized Attached to Attached to Attached
    [Show full text]
  • CHEM 345 Problem Set 18 Key 1.) Write the Mechanism for The
    CHEM 345 Problem Set 18 Key 1.) Write the mechanism for the following reactions. O a.) KCN EtOH O OH racemic 1.) Write the mechanism for the following reactions. b.) KCN AcOH O NC OH racemic O c.) N S R O NEt3 OH racemic 2.) What is the structure of AcOH?Why does changing the solvent from EtOH to AcOH make such a big difference? O OH AcOH acetic acid The pKa of acetic acid is approximately 5. The pKa of ethanol is approximately 15. When you take a proton off of ethanol, you generate ethoxide which is about 1010 times stronger of a base than acetate. 3.) Give two instances when you need to use the thiazolium salt and triethylamine rather than KCN and EtOH. If the aldehydes contain an enolizable proton then you cannot use KCN/EtOH, instead you must use the thiazolium. Also, if the electrophile is a Michael acceptor to give a 1,4 dicarbonyl, then the thiazolium catalyst should be used. 4.) Break the following compound down as far as you can using Aldol, Michael, and Claisen reactions. Above each retrosynthetic arrow, write the name of the reaction. O HO O HO Aldol O Michael HO O O HO O Aldol O O Aldol HO O O HO Michael O O O Aldol There are other possibilities for order. O O HO Aldol O O 5.) Synthesize the following molecules. All carbons in the molecules must come from benzene or compounds with 5C’s or less. a.) O H2SO4 O HNO3 O2N AlCl3 O O SOCl2 HO Cl H2CrO4 1.) BuLi, Et2O + O 2.) H3O HO b.) O O O Cl + H3O NaOEt, EtOH O O O O Cl O AlCl3 Cl Cl AlCl3 Cl2 c.) O OMe NaOMe MeOH O O 1.) POCl3, DMF 2.) H2O OMe OMe O AlCl3 MeI Cl ONa HCl NaOH ZnHg 1.) NaOH + mcpba O 2.) H3O O OH O O AlCl3 Cl 6.) Write the mechanism for the following reactions.
    [Show full text]
  • Socit Chimique De France 2014 Prize Winners
    Angewandte. Angewandte News Chemie Socit Chimique de France 2014 Prize Nazario Martn (Universidad Complutense de Winners Madrid) is the winner of the Prix franco-espagnol Awarded … Miguel Cataln–Paul Sabatier. Martn was featured The Socit Chimique de France has announced its here when he was awarded the 2012 EuCheMS 2014 prize winners. We congratulate all the awar- Lectureship.[4a] Martn is on the International dees and feature our authors and referees here. Advisory Boards of Chemistry—An Asian Journal, Max Malacria (Institut de Chimie des Substan- ChemPlusChem, and ChemSusChem. His report on ces Naturelles; ICSN) is the winner of the Prix modified single-wall nanotubes was recently fea- Joseph Achille Le Bel, which is awarded to tured on the cover of Chemistry—A European recognize internationally recognized research. Mal- Journal.[4b] acria studied at the Universit Aix-Marseille III, Michael Holzinger (Universit Joseph Four- where he completed his PhD under the supervision nier, Grenoble 1; UJF) is the winner of the Prix M. Malacria of Marcel Bertrand in 1974. From 1974–1981, he jeune chercheur from the Analytical Chemistry was matre-assistant with Jacques Gore at the Division. Holzinger carried out his PhD at the Universit Claude Bernard Lyon 1 (UCBL), and Friedrich-Alexander-Universitt Erlangen-Nrn- from 1981–1983, he carried out postdoctoral berg. After postdoctoral research at the Universit research with K. Peter C. Vollhardt at the Univer- Montpellier 2 (UM2) and the Max Planck Institute sity of California, Berkeley. He returned to the for Solid-State Research, and working at Robert UCBL as matre de conferences in 1983, and was Bosch, he joined Serge Cosniers group at the UJF made professor at the Universit Pierre et Marie as a CNRS charg de recherche.
    [Show full text]
  • Reactions of Benzene & Its Derivatives
    Organic Lecture Series ReactionsReactions ofof BenzeneBenzene && ItsIts DerivativesDerivatives Chapter 22 1 Organic Lecture Series Reactions of Benzene The most characteristic reaction of aromatic compounds is substitution at a ring carbon: Halogenation: FeCl3 H + Cl2 Cl + HCl Chlorobenzene Nitration: H2 SO4 HNO+ HNO3 2 + H2 O Nitrobenzene 2 Organic Lecture Series Reactions of Benzene Sulfonation: H 2 SO4 HSO+ SO3 3 H Benzenesulfonic acid Alkylation: AlX3 H + RX R + HX An alkylbenzene Acylation: O O AlX H + RCX 3 CR + HX An acylbenzene 3 Organic Lecture Series Carbon-Carbon Bond Formations: R RCl AlCl3 Arenes Alkylbenzenes 4 Organic Lecture Series Electrophilic Aromatic Substitution • Electrophilic aromatic substitution: a reaction in which a hydrogen atom of an aromatic ring is replaced by an electrophile H E + + + E + H • In this section: – several common types of electrophiles – how each is generated – the mechanism by which each replaces hydrogen 5 Organic Lecture Series EAS: General Mechanism • A general mechanism slow, rate + determining H Step 1: H + E+ E El e ctro - Resonance-stabilized phile cation intermediate + H fast Step 2: E + H+ E • Key question: What is the electrophile and how is it generated? 6 Organic Lecture Series + + 7 Organic Lecture Series Chlorination Step 1: formation of a chloronium ion Cl Cl + + - - Cl Cl+ Fe Cl Cl Cl Fe Cl Cl Fe Cl4 Cl Cl Chlorine Ferric chloride A molecular complex An ion pair (a Lewis (a Lewis with a positive charge containing a base) acid) on ch lorine ch loronium ion Step 2: attack of
    [Show full text]
  • Chapter 20 the Carbonyl Can Be an Electrophile, It Can Be Attacked. It Can Occur Under Basic Or Acidic Conditions
    Chapter 20 The carbonyl can be an electrophile, it can be attacked. It can occur under basic or acidic conditions. Basic Conditions: H O 1. Nu- O 2. H2O workup Nu Nu: HOH O : Nu Acidic Conditions: H+ H O : 1. H+, Nu: O Nu H + O OH Nu Nu: Hydride reductions. Basic conditions, H- is the nucleophile Ketones and aldehydes react w/ LiAlH4. H O 1. LiAlH4 O 2. H2O workup - H H: HOH O : H Esters and acid chlorides react w/ LiAlH4. H O 1. LiAlH4 O 2. H O workup OMe 2 H - H H: HOH O : O O : OMe H H H - H H: There are many sources of hydride with various reactivities Hydride Aldehyde Ketone Ester Amide Carboxyllic Acid Donors acid/ acid salt halide LiAlH4 Alcohol Alcohol Alcohol Amine Alcohol Alcohol LiAlH(OtBu)3 Alcohol Alcohol Alcohol - (too slow) N.R. Aldehyde NaBH4 Alcohol Alcohol N.R. N.R. N.R. ? NaBH3CN Alcohol N.R. N.R. N.R. N.R. ? DIBAL-H Alcohol Alcohol Aldehyde * Aldehyde* Alcohol ? * Stoichiometry must be carefully controlled. H2, Pd/C reacts preferentially with carbon-carbon double bonds. Carbon Nucleophiles: - Both of the following create reagents that act like CH3 . EtBr + 2Li →EtLi + LiBr EtBr + Mg → EtMgBr Alkyne nucleophiles. - + CH3C≡CH + NaNH2→ CH3C≡C: Na + NH3 - + CH3C≡CH + CH3Li → CH3C≡C: Li + CH4↑ CH3C≡CH + CH3MgBr → CH3C≡CMgBr + CH4↑ Ketones and aldehydes react w/ these carbon nucleophiles. H O 1. H3C CCMgBr O 2. H2O workup - C CH3CC: C CH HOH 3 O : Esters and acid chlorides react w/ these carbon nucleophiles.
    [Show full text]
  • Using Carbon Dioxide As a Building Block in Organic Synthesis
    REVIEW Received 10 Jul 2014 | Accepted 21 Nov 2014 | Published 20 Jan 2015 DOI: 10.1038/ncomms6933 Using carbon dioxide as a building block in organic synthesis Qiang Liu1, Lipeng Wu1, Ralf Jackstell1 & Matthias Beller1 Carbon dioxide exits in the atmosphere and is produced by the combustion of fossil fuels, the fermentation of sugars and the respiration of all living organisms. An active goal in organic synthesis is to take this carbon—trapped in a waste product—and re-use it to build useful chemicals. Recent advances in organometallic chemistry and catalysis provide effective means for the chemical transformation of CO2 and its incorporation into synthetic organic molecules under mild conditions. Such a use of carbon dioxide as a renewable one-carbon (C1) building block in organic synthesis could contribute to a more sustainable use of resources. more sensible resource management is the prerequisite for the sustainable development of future generations. However, when dealing with the feedstock of the chemical Aindustry, the level of sustainability is still far from satisfactory. Until now, the vast majority of carbon resources are based on crude oil, natural gas and coal. In addition to biomass, CO2 offers the possibility to create a renewable carbon economy. Since pre-industrial times, the amount of CO2 has steadily increased and nowadays CO2 is a component of greenhouse gases, which are primarily responsible for the rise in atmospheric temperature and probably abnormal changes in the global climate. This increase in CO2 concentration is largely due to the combustion of fossil fuels, which are required to meet the world’s energy demand1.
    [Show full text]
  • Reactions of Aromatic Compounds Just Like an Alkene, Benzene Has Clouds of  Electrons Above and Below Its Sigma Bond Framework
    Reactions of Aromatic Compounds Just like an alkene, benzene has clouds of electrons above and below its sigma bond framework. Although the electrons are in a stable aromatic system, they are still available for reaction with strong electrophiles. This generates a carbocation which is resonance stabilized (but not aromatic). This cation is called a sigma complex because the electrophile is joined to the benzene ring through a new sigma bond. The sigma complex (also called an arenium ion) is not aromatic since it contains an sp3 carbon (which disrupts the required loop of p orbitals). Ch17 Reactions of Aromatic Compounds (landscape).docx Page1 The loss of aromaticity required to form the sigma complex explains the highly endothermic nature of the first step. (That is why we require strong electrophiles for reaction). The sigma complex wishes to regain its aromaticity, and it may do so by either a reversal of the first step (i.e. regenerate the starting material) or by loss of the proton on the sp3 carbon (leading to a substitution product). When a reaction proceeds this way, it is electrophilic aromatic substitution. There are a wide variety of electrophiles that can be introduced into a benzene ring in this way, and so electrophilic aromatic substitution is a very important method for the synthesis of substituted aromatic compounds. Ch17 Reactions of Aromatic Compounds (landscape).docx Page2 Bromination of Benzene Bromination follows the same general mechanism for the electrophilic aromatic substitution (EAS). Bromine itself is not electrophilic enough to react with benzene. But the addition of a strong Lewis acid (electron pair acceptor), such as FeBr3, catalyses the reaction, and leads to the substitution product.
    [Show full text]
  • A Nobel Synthesis
    MILESTONES IN CHEMISTRY Ian Grayson A nobel synthesis IAN GRAYSON Evonik Degussa GmbH, Rodenbacher Chaussee 4, Hanau-Wolfgang, 63457, Germany he first Nobel Prize for chemistry was because it is a scientific challenge, as he awarded in 1901 (to Jacobus van’t Hoff). described in his Nobel lecture: “The synthesis T Up to 2010, the chemistry prize has been of brazilin would have no industrial value; awarded 102 times, to 160 laureates, of whom its biological importance is problematical, only four have been women (1). The most but it is worth while to attempt it for the prominent area for awarding the Nobel Prize sufficient reason that we have no idea how for chemistry has been in organic chemistry, in to accomplish the task” (4). which the Nobel committee includes natural Continuing the list of Nobel Laureates in products, synthesis, catalysis, and polymers. organic synthesis we arrive next at R. B. This amounts to 24 of the prizes. Reading the Woodward. Considered by many the greatest achievements of the earlier organic chemists organic chemist of the 20th century, he who were recipients of the prize, we see that devised syntheses of numerous natural they were drawn to synthesis by the structural Alfred Nobel, 1833-1896 products, including lysergic acid, quinine, analysis and characterisation of natural cortisone and strychnine (Figure 1). 6 compounds. In order to prove the structure conclusively, some In collaboration with Albert Eschenmoser, he achieved the synthesis, even if only a partial synthesis, had to be attempted. It is synthesis of vitamin B12, a mammoth task involving nearly 100 impressive to read of some of the structures which were deduced students and post-docs over many years.
    [Show full text]
  • Nuclear Magnetic Resonance Approaches in the Study of 2-Oxo Acid Dehydrogenase Multienzyme Complexes— a Literature Review
    Molecules 2013, 18, 11873-11903; doi:10.3390/molecules181011873 OPEN ACCESS molecules ISSN 1420-3049 www.mdpi.com/journal/molecules Review Nuclear Magnetic Resonance Approaches in the Study of 2-Oxo Acid Dehydrogenase Multienzyme Complexes— A Literature Review Sowmini Kumaran 1, Mulchand S. Patel 2 and Frank Jordan 1,* 1 Department of Chemistry, Rutgers University, Newark, NJ 07102, USA 2 Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, NY 14214, USA * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +1-973-353-5470; Fax: +1-973-353-1264. Received: 30 July 2013; in revised form: 14 September 2013 / Accepted: 16 September 2013 / Published: 26 September 2013 Abstract: The 2-oxoacid dehydrogenase complexes (ODHc) consist of multiple copies of three enzyme components: E1, a 2-oxoacid decarboxylase; E2, dihydrolipoyl acyl-transferase; and E3, dihydrolipoyl dehydrogenase, that together catalyze the oxidative decarboxylation of 2-oxoacids, in the presence of thiamin diphosphate (ThDP), coenzyme A 2+ + (CoA), Mg and NAD , to generate CO2, NADH and the corresponding acyl-CoA. The structural scaffold of the complex is provided by E2, with E1 and E3 bound around the periphery. The three principal members of the family are pyruvate dehydrogenase (PDHc), 2-oxoglutarate dehydrogenase (OGDHc) and branched-chain 2-oxo acid dehydrogenase (BCKDHc). In this review, we report application of NMR-based approaches to both mechanistic and structural issues concerning these complexes. These studies revealed the nature and reactivity of transient intermediates on the enzymatic pathway and provided site-specific information on the architecture and binding specificity of the domain interfaces using solubilized truncated domain constructs of the multi-domain E2 component in its interactions with the E1 and E3 components.
    [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]