DOCSLIB.ORG

Organic Chemistry 1 Lecture 8

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Organic Chemistry 1 Lecture 8 CHEM 232 University of Illinois Organic Chemistry I at Chicago UIC Organic Chemistry 1 Lecture 8 Instructor: Prof. Duncan Wardrop Time/Day: T & R, 12:30-1:45 p.m. February 04, 2010 1 Self Test Question Which of the following transformations is unlikely to generate the product indicated? OH HCl Cl a. 25 ºC primary alcohols HCl A. a. and HCl are insufficiently x b. OH 25 ºC Cl reactive B. b. SOCl2 O O c. OH Cl C. c. K2CO3 Cl D. d. d. Cl2 hν University of Slide CHEM 232, Spring 2010 2 Illinois at Chicago UIC Lecture 8: February 4 2 Compound “b.” is a primary alcohol, which are insufciently reactive to undergo reaction with hydrogen chloride. Primary alcohols do, however, react with thionyl chloride (SOCl2) to form chlorides and so the transformation shown in “c” will proceed successfully Compound “a” is tertiary alcohol and consequently reacts with HCl. Substitution Reaction hydroxyl group halide R O H + H X R X + H O H alcohol hydrogen alkyl water halide halide Hydroxyl group is being substituted (replaced with) a halide University of Slide CHEM 232, Spring 2010 3 Illinois at Chicago UIC Lecture 8: February 4 3 CHEM 232 University of Illinois Organic Chemistry I at Chicago UIC Mechanisms of Substitution Reactions Sections: 4.8-4.11 4 Substitution: How Does it Happen? break bond break bond make bond make bond R O H + H X R X + H O H alcohol hydrogen alkyl halide water halide mechanism: a generally accepted series of elementary steps that show the order of bond breaking and bond making elementary step: a bond making and/or bond breaking step that only involves one transition state University of Slide CHEM 232, Spring 2010 5 Illinois at Chicago UIC Lecture 8: February 4 5 Ingold-Hughes Mechanistic Designators Designates # molecularity Designates type of process Letter Nucleophilic N or E or Electrophilic Example Me Me Substitution, H-Br Me Me nucleophilic, OH Br SN1 Me Me 1st order Rate = k x [t-BuOH] University of Slide CHEM 232, Spring 2010 6 Illinois at Chicago UIC Lecture 8: February 4 6 Nucleophilic Substitution (SN1) Step One Proton Transfer (Protonation) fast & reversible H O H Cl O Cl H H pKa = -3.9 alkyloxonium ion University of Slide CHEM 232, Spring 2010 7 Illinois at Chicago UIC Lecture 8: February 4 7 this is an acid-base reaction; product is an alkoxonium ion exothermic and fast (proton transfer is among the fastest processes in organic chemistry) rate of individual step =k x [alcohol] x [HX]; two reactants = bimolecular (2nd order) oxonium ion is an intermediate in the overall reaction Step One Potential Energy Diagram Step One Proton Transfer (Protonation) transition state: energy maximum along reaction coordinate for one elementary step; usually involves partial bond making and partial bond breaking intermediate: energy minimum along the reaction coordinate; species with a finite lifetime; neither reactant, nor product Hammond Postulate: structure of the transition state “looks” most like its closest energy reactant or intermediate University of Slide CHEM 232, Spring 2010 8 Illinois at Chicago UIC Lecture 8: February 4 8 Mechanism: Nucleophilic Substitution (SN1) Step Two Dissociation (Ionization) slow H Me Me O H2O H Me carbocation (t-butyl cation) University of Slide CHEM 232, Spring 2010 9 Illinois at Chicago UIC Lecture 8: February 4 9 breaking a carbon-oxygen bond slowest (rate determining) step in entire mechanism; endothermic rate=k[oxonium ion]; one reactant = unimolecular (1st order) Step Two Potential Energy Diagram Step Two Dissociation (Ionization) • largest activation energy (Ea) • endothermic, slowest • carbocation intermediate is much higher in energy than an oxonium ion • carbocations do not have a full octet, whereas oxonium ions do • structure of transition state most resembles the closest energy neighbor, the carbocation (Hammond Post.) University of Slide CHEM 232, Spring 2010 10 Illinois at Chicago UIC Lecture 8: February 4 10 Mechanism: Nucleophilic Substitution (SN1) Step Three Carbocation Capture Me Me fast Cl Cl Me carbocation t-butyl chloride (t-butyl cation) Cation = Electrophile Anion = Nucleophile University of Slide CHEM 232, Spring 2010 11 Illinois at Chicago UIC Lecture 8: February 4 11 exothermic and fast; neutral products much lower in NRG small activation energy; negative charge to positive charge transition state looks most like carbocation since they are closest in energy rate = k x [carbocation][halide]; two reactants = bimolecular Step Three Potential Energy Diagram Step Three Carbocation Capture • fast step because small activation energy; positive and negative atoms bond fast • products are much lower in energy since they are neutral; exothermic reaction • transition state looks most like its closest neighbor, the carbocation intermediate (very little C-Cl bond formation at transition state) (Hammond Postulate) University of Slide CHEM 232, Spring 2010 12 Illinois at Chicago UIC Lecture 8: February 4 12 Nucleophiles Add to Electrophiles nucleophile: nucleus loving; Lewis base; electron pair donor; forms bonds with a nucleus that can accept electrons; does not necessarily have to be negatively charged; has available, !lled orbitals! electrophile: electron loving; Lewis acid; electron pair acceptor; forms bonds by accepting electrons from other atoms; does not necessarily have to be positively charged; has available, empty orbitals! Cation is Electrophile Me Me empty 2pz orbital Cl Chloride is Nucleophile Me filled n orbital (: = lone pair) University of Slide CHEM 232, Spring 2010 13 Illinois at Chicago UIC Lecture 8: February 4 13 Complete Mechanism fast & reversible H O H Cl O Cl H H alkyloxonium ion slow Me Me fast Cl Cl Me carbocation H O t-butyl chloride (t-butyl cation) 2 University of Slide CHEM 232, Spring 2010 14 Illinois at Chicago UIC Lecture 8: February 4 14 Complete Potential Energy Diagram • mechanism only valid for 3º & 2º alcohols • reaction is only as fast as its slowest step rate • slowest step (largest Ea) = determining step (RDS) rate determining step (RDS) • here, slowest step is carbocation formation • here, RDS is unimolecular Protonation carbocation formation carbocation capture University of Slide CHEM 232, Spring 2010 15 Illinois at Chicago UIC Lecture 8: February 4 15 Naming the Mechanism: Ingold Notation R O H + H X R X + H O H alcohol hydrogen alkyl halide water halide SN1 1: 1st order S: Substitution N: Nucleophilic (unimolecular) the RDS is the alcohol the halide doing the carbocation functional groups is substitution is a formation; this step is being substituted nucleophile unimolecular (1st with a halide order) University of Slide CHEM 232, Spring 2010 16 Illinois at Chicago UIC Lecture 8: February 4 16 Self Test Question Consider the SN1 mechanism for the formation of 2- bromobutane. Which structure best represents the highest energy transition state in this mechanism? Br a. c. + A. a. O H Br H O H H H δ+ δ− B. b. C. c. δ+ + Br + Br D. d. b. O d. O H H H H δ+ University of Slide CHEM 232, Spring 2010 17 Illinois at Chicago UIC Lecture 8: February 4 17 Structure of Carbocations • carbocations are high energy intermediates; hard, but not impossible to isolate 2pZ • carbon is sp2-hybridized with a single, H unoccupied 2pZ orbital; 6 valence electrons H3C C • planar structure : three bonds to carbon are H at 120º angles from each other and 90º to empty p-orbital; VSEPR • nucleophiles add to either lobe of the empty carbocations can be stabilized by inductive effects and hyperconjugation p-orbital; since it is "at, there is no preference to which side nucleophile adds University of Slide CHEM 232, Spring 2010 18 Illinois at Chicago UIC Lecture 8: February 4 18 Stability of Carbocations 1. Inductive Effects electron withdrawal or electron donation that is transmitted through σ- bonds; polarization of σ-bonds • electron donation through 1º cation σ-bonds toward δ+ carbocation delocalizes δ+ H charge (spreads out) • C-C σ-bonds are more H3C C polarizable, therefore δ+ donate more electron H density through σ-bonds • more C-C σ-bonds = more stable carbocation University of Slide CHEM 232, Spring 2010 19 Illinois at Chicago UIC Lecture 8: February 4 19 Stability of Carbocations 1. Inductive Effects Since C-C σ-bonds are more polarizable than C-H bonds, the additional of more alkyl groups leads to stabilization of the cation 2º cation 3º cation δ+ δ+ δ+ CH3 δ+ CH3 H3C C H3C C H δ+ CH3 δ+ University of Slide CHEM 232, Spring 2010 20 Illinois at Chicago UIC Lecture 8: February 4 20 Stability of Carbocations 2. Hyperconjugation stabilizing interaction that results from the interaction of the electrons in a σ-bond (C–H or C–C bond ) with an adjacent empty (or partially !lled) orbital. Leads to the formation of an extended molecular orbital that increases the stability of the system filled σ orbital • stabilization results from σ-donation to empty p orbital of planar carbocation empty • electron donation through σ-bonds H p orbital toward carbocation delocalizes charge H (spreads out) C C H H • methyl cations cannot be stabilized by hyperconjugation since σ-bonds are H perpendicular to the empty p orbital 1º cation University of Slide CHEM 232, Spring 2010 21 Illinois at Chicago UIC Lecture 8: February 4 21 Stability of Carbocations 2. Hyperconjugation filled empty σ orbital 2pZ orbital empty C-H 2pZ H p orbital bonding y (filled) g H r e C C n E H H Stabilization resulting from H σ hyperconjugation University of Slide CHEM 232, Spring 2010 22 Illinois at Chicago UIC Lecture 8: February 4 22 Stability of Carbocations H H CH3 H H H3C CH2 CH2 CH2 C C C C C C H H H CH2 H CH2 H H H H CH3 H 2º carbocation 3º carbocation 3º carbocation 2 C-H bond 3 C-H bond 3 C-C or C-H bond hyperconjugative hyperconjugative hyperconjugative donors donors donors University of Slide CHEM 232, Spring 2010 23 Illinois at Chicago UIC Lecture 8: February 4 23 i>Clicker Question Rank the following carbocations in order of increasing stability? A.
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]
  • 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]
  • 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]
  • Developing a S Ystem to Study the Dynamics of the Heterolysis of Psubstituted Radicals in Terms of Magnetic Field Effects
    Developing a S ystem to Study the Dynamics of the Heterolysis of PSubstituted Radicals in terms of Magnetic Field Effects by Elaine K. Adams Submitted in partial fulfiiIlment of the requirements for the degree of Master of Science Dalhousie University Halifax, Nova Scotia September, 1998 @ Copyright by Elaine K. Adams, 1998 National hirary Bibliothèque nationale du Canada Acquisitions and Acquisiins et Biliograpfii Services seMces bibliographiques The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or seli reproduire, prêter, distriiuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de micro fi ch el^ de reproduction sur papier ou sur fonnat électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fkom it Ni la thése ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Table of Contents List of Figures ........................................................................................ vi ... List of Tables ........................................................................................ xm 1.1 General Introduction .......................................................................
    [Show full text]
  • Coordinate Covalent C F B Bonding in Phenylborates and Latent Formation of Phenyl Anions from Phenylboronic Acid†
    J. Phys. Chem. A 2006, 110, 1295-1304 1295 Coordinate Covalent C f B Bonding in Phenylborates and Latent Formation of Phenyl Anions from Phenylboronic Acid† Rainer Glaser* and Nathan Knotts Department of Chemistry, UniVersity of MissourisColumbia, Columbia, Missouri 65211 ReceiVed: July 4, 2005; In Final Form: August 8, 2005 The results are reported of a theoretical study of the addition of small nucleophiles Nu- (HO-,F-)to - phenylboronic acid Ph-B(OH)2 and of the stability of the resulting complexes [Ph-B(OH)2Nu] with regard - - - - - to Ph-B heterolysis [Ph-B(OH)2Nu] f Ph + B(OH)2Nu as well as Nu /Ph substitution [Ph-B(OH)2Nu] - - - + Nu f Ph + [B(OH)2Nu2] . These reactions are of fundamental importance for the Suzuki-Miyaura cross-coupling reaction and many other processes in chemistry and biology that involve phenylboronic acids. The species were characterized by potential energy surface analysis (B3LYP/6-31+G*), examined by electronic structure analysis (B3LYP/6-311++G**), and reaction energies (CCSD/6-311++G**) and solvation energies - (PCM and IPCM, B3LYP/6-311++G**) were determined. It is shown that Ph-B bonding in [Ph-B(OH)2Nu] is coordinate covalent and rather weak (<50 kcal‚mol-1). The coordinate covalent bonding is large enough to inhibit unimolecular dissociation and bimolecular nucleophile-assisted phenyl anion liberation is slowed greatly by the negative charge on the borate’s periphery. The latter is the major reason for the extraordinary differences in the kinetic stabilities of diazonium ions and borates in nucleophilic substitution reactions despite their rather similar coordinate covalent bond strengths.
    [Show full text]