Organic Chemistry: Alkenes and Reactions
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Questions and Answers

What type of addition occurs when halogens, such as Cl and Br, are added to a double bond in the absence of light?

  • Syn addition
  • Anti addition (correct)
  • Cis addition
  • Markovnikov addition
  • In the hydration of alkenes to form alcohol, what role does an acid catalyst like H2SO4 play in the reaction?

  • It facilitates the addition of water. (correct)
  • It promotes rearrangement of carbocations.
  • It drives the reaction towards dehydration.
  • It increases the temperature of the reaction.
  • What effect does the presence of an electron-withdrawing group have on the addition of electrophiles to an alkene?

  • It enhances the stability of carbocation intermediates.
  • It leads to Markovnikov addition.
  • It causes Anti-Markovnikov addition. (correct)
  • It forces the reaction to go backward.
  • Why is acid-catalyzed hydration of alkenes rarely used in alcohol preparation?

    <p>There is a risk of rearrangement of the carbocation.</p> Signup and view all the answers

    What is a characteristic feature of the addition of water to alkenes?

    <p>It proceeds via the formation of a carbocation.</p> Signup and view all the answers

    What is the primary result of using hot alkaline KMnO4 on 2-alkenes?

    <p>Oxidation into acid salts</p> Signup and view all the answers

    In which condition does the halogenation of alkenes take place via a free radical mechanism?

    <p>Gaseous state at high temperature</p> Signup and view all the answers

    What effect does heating have on the reaction of 1-propene with KMnO4/OH?

    <p>Enhances oxidative cleavage to CO2 and H2O</p> Signup and view all the answers

    What is indicated if the brown color of bromine disappears upon adding a hydrocarbon?

    <p>The hydrocarbon is an alkene.</p> Signup and view all the answers

    Which reagent is used in the Bayer test for unsaturation?

    <p>Aqueous potassium permanganate</p> Signup and view all the answers

    What type of reaction occurs when alkenes with disubstituted carbon atoms are oxidized?

    <p>Conversion into ketones</p> Signup and view all the answers

    Which of the following processes results in a substitution reaction for alkenes?

    <p>Halogenation in the gaseous state</p> Signup and view all the answers

    What is formed when an alkene reacts with a peroxyacid?

    <p>An epoxide</p> Signup and view all the answers

    What is oxidized to CO2 and H2O when 1-alkenes undergo oxidation with KMnO4?

    <p>Terminal CH2</p> Signup and view all the answers

    What is the result of oxidative cleavage of an alkene using warm concentrated acidic KMnO4?

    <p>Formation of carbon dioxide and acids</p> Signup and view all the answers

    Which statement about oxidative cleavage of alkenes is true?

    <p>It can produce CO2 and H2O from alkenes.</p> Signup and view all the answers

    Which type of diols are produced from the reaction of alkenes with cold, dilute aqueous potassium permanganate?

    <p>Cis or syn diols</p> Signup and view all the answers

    What happens to disubstituted carbons during oxidative cleavage?

    <p>They become ketones.</p> Signup and view all the answers

    What key characteristic differentiates the ionic addition reaction from the free radical halogenation mechanism?

    <p>Temperature conditions</p> Signup and view all the answers

    Which statement about the oxidative cleavage process is FALSE?

    <p>Monosubstituted carbons become ketones.</p> Signup and view all the answers

    What is the main characteristic of a trans or anti diol formation?

    <p>Result of epoxide formation and subsequent acid hydrolysis.</p> Signup and view all the answers

    Study Notes

    Oxidation with σ bond cleavage:

    • Hot, alkaline KMnO4 oxidizes 2-alkenes into acid salts
    • Terminal CH2 in 1-alkene is oxidized into CO2 and H2O
    • Alkenes with disubstituted C atom of a double bond are oxidized into ketones

    Halogenation of alkenes:

    • Halogenation of alkenes at high temperature in the gaseous state proceeds by a free radical mechanism resulting in substitution reaction.
    • Ionic addition reaction occurs at low temperatures and in the absence of light and generally in the liquid phase.

    Oxidation Reaction:

    • Oxidation to 1,2-diols (vicinal diols) (glycols) where the Pi bond is only broken with the formation of 2 new σ bonds bearing OH groups
    • Syn-diols are formed using cold, dilute aqueous potassium permanganate followed by hydrolysis with base (Bayer test for unsaturation)
    • Trans-diols (epoxide formation) are formed when an alkene reacts with a peroxyacid (peroxybenzoic) to form an epoxide followed by acid hydrolysis

    Epoxide Formation:

    • Nobel Prize in Chemistry 2001 was awarded to Karl Sharpless for his work in this field

    Oxidative Cleavage:

    • Both the pi and sigma bonds break. C=C becomes C=O
    • Using warm concentrated acidic KMnO4
    • Used to determine the position of a double bond in an unknown
    • Permanganate is a strong oxidizing agent
    • Glycol initially formed is further oxidized
    • Disubstituted carbons become ketones
    • Monosubstituted carbons become carboxylic acids
    • Terminal =CH2 becomes CO2.
    • More general Markovnikov’s Rule: in an electrophilic addition to an alkene, the electrophile adds in such a way as to form the most stable intermediate (carbocation)
    • HI> HBr> HCl add to alkenes to form Markovnikov products

    Anti-Markovnikov addition:

    • Presence of an electron-withdrawing (-I effect) group adjacent to the olefinc (double bond) e,g CF3 , NO2 ,C≡N and COOH make the addition anti-Markovnikov

    Addition of Water to Alkenes:

    • Hydration of Alkenes results in alcohol formation
    • The reaction is the reverse of dehydration of alcohol
    • Use very dilute solutions of H2SO4 or H3PO4 to drive equilibrium toward hydration (acid catalyst reaction)

    Acid catalyst hydration of alkene

    • Is seldom used in alcohol preparation due to the possibility of rearrangement

    Addition of Halogens (unsaturation test):

    • Cl2, Br2 (in CCl4) add to a double bond in the absence of light and at room temperature to form a vicinal dibromide
    • Anti addition, so reaction is stereospecific

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    Description

    Explore the fascinating world of organic chemistry focusing on alkenes and their reactions. This quiz covers oxidation processes, halogenation, and the formation of diols and epoxides. Test your understanding of these key concepts in organic reactions.

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