Hydroboration and Hydrogenation Reactions
48 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the regioselectivity of the hydroboration reaction?

  • Anti-Markovnikov regioselectivity (correct)
  • Random regioselectivity
  • Markovnikov regioselectivity
  • No specific regioselectivity

    • How many equivalents of alkene react with one BH3 in hydroboration?

  • One equivalent
  • Two equivalents
  • Three equivalents (correct)
  • Four equivalents

    • What type of addition occurs during hydroboration?

  • No addition
  • Syn addition (correct)
  • Random addition
  • Anti addition

    • What effect does sterics have on hydroboration?

    <p>It influences the regioselectivity</p> Signup and view all the answers

    When only one chiral center forms during hydroboration, what is produced?

    <p>A pair of enantiomers</p> Signup and view all the answers

    What is required for the catalytic hydrogenation process?

    <p>A metal catalyst</p> Signup and view all the answers

    What is the stereochemical outcome of the hydrogenation process?

    <p>Only syn addition is observed</p> Signup and view all the answers

    In hydrogenation reactions, what type of compounds are formed?

    <p>Alkanes</p> Signup and view all the answers

    What is the primary reason that the addition of H2 without a metal catalyst is slow?

    <p>High activation energy</p> Signup and view all the answers

    What is the outcome of adding H2 to a symmetrical alkene?

    <p>A meso compound</p> Signup and view all the answers

    Which type of catalyst does not dissolve in the reaction medium?

    <p>Heterogeneous catalyst</p> Signup and view all the answers

    What is the effect of using a chiral catalyst in asymmetric hydrogenation?

    <p>Synthesis of only one enantiomer as the major product</p> Signup and view all the answers

    Who developed a synthesis of L-dopa using asymmetric hydrogenation?

    <p>William S. Knowles</p> Signup and view all the answers

    What is the role of the metal surface in catalytic hydrogenation?

    <p>To bind H2 and the alkene for syn addition</p> Signup and view all the answers

    What happens when phosphine ligands are replaced with chiral phosphine ligands in the Wilkinson catalyst?

    <p>Only one enantiomer is synthesized as the major product</p> Signup and view all the answers

    In the context of catalytic hydrogenation, what is meant by 'syn addition'?

    <p>H atoms are added to the same face of the alkene</p> Signup and view all the answers

    What is the main reason for the formation of the Markovnikov product during hydrohalogenation?

    <p>Presence of low energy transition state</p> Signup and view all the answers

    Which of the following statements about the products of hydrohalogenation is true?

    <p>Enantiomers of the Markovnikov product are formed in equal amounts</p> Signup and view all the answers

    What factor primarily influences the rearrangement of carbocations during hydrohalogenation?

    <p>The possibility of forming more stable carbocations</p> Signup and view all the answers

    Which acid is commonly used as a catalyst in acid-catalyzed hydration reactions?

    <p>Sulfuric acid</p> Signup and view all the answers

    Which mechanism pathway leads to the formation of the anti-Markovnikov product?

    <p>Direct nucleophilic attack pathway</p> Signup and view all the answers

    How does the stability of the carbocation intermediate affect the reaction rate in hydrohalogenation?

    <p>More stable carbocations lead to faster reactions</p> Signup and view all the answers

    During hydrohalogenation, what is a significant consequence of carbocation rearrangements?

    <p>Increase in reaction yield</p> Signup and view all the answers

    What occurs at the π bond during acid-catalyzed hydration?

    <p>Ionic addition of components of water happens</p> Signup and view all the answers

    What is formed when halogenation is conducted in water?

    <p>Halohydrin</p> Signup and view all the answers

    In the formation of halohydrins, which species acts as the nucleophile?

    <p>H2O</p> Signup and view all the answers

    What determines the regioselectivity in halohydrin formation?

    <p>The substitution pattern of the carbon atoms</p> Signup and view all the answers

    What is the role of water in the formation of bromohydrins and chlorohydrins?

    <p>It acts as a nucleophile to attack bromonium ion</p> Signup and view all the answers

    In the mechanism of anti dihydroxylation, what is the first step?

    <p>Formation of an epoxide from an alkene</p> Signup and view all the answers

    Why does the more-substituted carbon get attacked faster during halohydrin formation?

    <p>It possesses greater stability due to cationic character</p> Signup and view all the answers

    What occurs after the nucleophilic attack in the formation of a bromohydrin?

    <p>Water is deprotonated to yield a neutral product</p> Signup and view all the answers

    Which reagent is necessary for the conversion of an alkene to an epoxide in anti dihydroxylation?

    <p>Peroxyacid</p> Signup and view all the answers

    What type of products do the intermediates with ring strain and a +1 formal charge yield?

    <p>Anti products</p> Signup and view all the answers

    Which of the following reagents is used as a co-oxidant in syn dihydroxylation to minimize the amount of OsO4 needed?

    <p>NMO</p> Signup and view all the answers

    What is the primary limitation of using potassium permanganate (KMnO4) in syn dihydroxylation?

    <p>It reacts with many functional groups</p> Signup and view all the answers

    What is a common reducing agent used in oxidative cleavage reactions?

    <p>Dimethyl sulfide (DMS)</p> Signup and view all the answers

    Which process involves the reaction of C=C double bonds with ozone?

    <p>Ozonolysis</p> Signup and view all the answers

    In predicting the products of addition reactions, what is one of the first steps to consider?

    <p>The reagents used</p> Signup and view all the answers

    What type of bond is primarily involved in the process of syn dihydroxylation?

    <p>Pi bond</p> Signup and view all the answers

    What is the outcome of attacks from the nucleophile during an SN2-like process?

    <p>The nucleophile attacks from the side opposite the leaving group</p> Signup and view all the answers

    What type of base should be chosen to perform an elimination reaction to achieve the desired alkene?

    <p>Non-bulky base</p> Signup and view all the answers

    What is the characteristic addition reaction outcome when changing the position of a halogen or OH?

    <p>Anti-Markovnikov addition</p> Signup and view all the answers

    Which process is required to produce the Hofmann product?

    <p>E2 elimination</p> Signup and view all the answers

    What transformation must be performed to the alcohol before using a bulky base for the elimination?

    <p>Conversion to a good leaving group</p> Signup and view all the answers

    Which of the following describes the type of addition reaction that occurs along with elimination to yield the Hofmann product?

    <p>Anti-Markovnikov addition</p> Signup and view all the answers

    What needs to be considered when combining processes to achieve the transformation of a reactant?

    <p>The specific conditions required for each process</p> Signup and view all the answers

    What type of addition occurs in the overall reaction sequence described for changing the position of a group?

    <p>Electrophilic addition</p> Signup and view all the answers

    What is the significance of the bulky base during the transformation process?

    <p>It impacts the sterics of the reaction</p> Signup and view all the answers

    Study Notes

    Introduction to Addition Reactions

    • Addition reactions are the opposite of elimination reactions
    • In addition reactions, a C=C π bond is converted to two new sigma bonds.
    • Key examples of addition reactions include hydrohalogenation, hydration, hydrogenation, halogenation, halohydrin formation, dihydroxylation.

    Alkenes in Nature and Industry

    • Naturally occurring acyclic alkenes include allicin (garlic odor) and geraniol (rose perfume). Farnesene is found on apple skin.
    • Cyclic and polycyclic alkenes include limonene (orange scent), a-pinene (turpentine), and cholesterol.
    • C=C double bond structures are often found in pheromones (muscalure, B-Farnesene, ectocarpene).
    • Alkenes serve as crucial precursors in the chemical industry, with ethylene and propylene being major products derived from petroleum cracking.

    Alkene Nomenclature

    • Alkene IUPAC names are similar to alkane names with minor modifications.
    • Identify the parent chain, including the C=C double bond.
    • Identify and name substituents.
    • Assign locants(and prefixes) to each substituent, prioritizing the lowest numbers for the C=C double bond.
    • List numbered substituents alphabetically, ignoring prefixes (except iso)
    • Place the C=C double bond locant before the parent name or before the -ene suffix.

    Addition vs Elimination

    • Addition and elimination are equilibrating reactions.
    • The favored side of the reaction depends on temperature.
    • Higher temperatures favor reactions that increase entropy.
    • Addition reactions are favored by enthalpy due to stronger sigma bonds.
    • Sigma (σ) bonds are stronger and more stable than pi (π) bonds

    Hydrohalogenation

    • Hydrohalogenation is the addition of H-X (HCl, HBr, or HI) to an alkene.
    • If the alkene is not symmetrical, two regioisomers are possible.
    • Regioselectivity for Markovnikov addition: The H atom is installed to the carbon atom with more hydrogen atoms already bonded.
    • Regioselectivity for Anti-Markovnikov addition: HBr can proceed through peroxides to give the Anti-Markovnikov product.

    Acid-Catalyzed Hydration

    • Acid-catalyzed hydration adds water (H and OH) across the π bond.
    • The reaction follows Markovnikov regioselectivity.
    • Sulfuric acid is a common acid catalyst.
    • The OH group adds to the more substituted carbon.

    Oxymercuration-Demercuration

    • Oxymercuration-demercuration is an alternative method of hydration that follows Markovnikov addition, avoiding carbocation rearrangements.
    • The mercuric ion is the Lewis acid in the reaction.
    • Nucleophilic attack by water yields an alcohol product.
    • NaBH4 is used to remove the mercury.

    Hydroboration-Oxidation

    • Hydroboration-oxidation adds H and OH to an alkene with anti-Markovnikov regioselectivity.
    • BH3 and THF are used in the reaction.
    • Sterics also influence regioselectivity.
    • Hydroboration-oxidation is stereoselective for syn addition, forming a pair of enantiomers or one chiral center.

    Catalytic Hydrogenation

    • Catalytic hydrogenation adds H2 across a C=C double bond, using a metal catalyst such as Pd or Pt.
    • The reaction produces a corresponding alkane.
    • Syn addition is observed.
    • The reaction is faster when metal catalysts are used due to lower reaction barrier.

    Halogenation

    • Halogenation is the addition of two halogen atoms (Cl2, Br2) across a C=C double bond.
    • Halogenation occurs via anti addition.
    • The mechanism involves a bromonium ion intermediate.

    Halohydrin Formation

    • Halohydrin formation occurs when halogenation happens in water.
    • Water acts as a nucleophile, attacking the bromonium ion.
    • The more substituted carbon gets the OH group.

    Anti Dihydroxylation

    • Oxidative cleavage adds water and alcohols to form epoxides (two-step procedure).
    • Peroxyacids (RCO3H) are used for the first step to form epoxides.
    • The reagents are deprotonated to give a neutral diol product.

    Syn Dihydroxylation

    • Syn dihydroxylation adds two OH groups across the C=C double bond in a concerted reaction.
    • OsO4 is used as a catalyst for the dihydroxylation with NMO or peroxide co-reactants for this reaction.
    • KMno4 can also result in dihydroxylation under mild conditions.

    Oxidative Cleavage

    • Oxidative cleavage is a reaction that breaks the C=C double bond.
    • Ozonolysis (using ozone(O3)) is a common oxidative cleavage method.
    • DMS is used as a reducing agent.

    Predicting Products of Addition Reactions

    • Analyze the reagents, determine regioselectivity or stereospecificity of the addition reaction, and determine the products in the reaction.
    • Practice with SkillBuilder 8.9

    One Step Syntheses

    • Plan syntheses by assessing the reactants and products to determine the necessary transformations including addition, elimination or substitution reactions.

    Changing Positions of a Halogen or OH

    • It may require more than one step to change the position of a halogen or OH group.
    • Carefully chose the reagents.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Organic Chemistry, Fourth Edition, Chapter 8 - Addition Reactions of Alkenes PDF

    Description

    Test your understanding of regioselectivity, sterics, and stereochemical outcomes in hydroboration and hydrogenation reactions. This quiz covers key concepts, including the role of catalysts and the effects of chirality in these processes.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser