Preparation of Alkenes
40 Questions
8 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 general formula for the alkene family?

  • CnH2n (correct)
  • CnH2n-1
  • CnH2n-2
  • CnH2n+1

    • What is the distinguishing feature of the alkene structure?

  • Carbon-hydrogen bond
  • Carbon-carbon triple bond
  • Carbon-carbon single bond
  • Carbon-carbon double bond (correct)

    • What is the strongest bond in the carbon-carbon double bond?

  • π bond
  • σ bond (correct)
  • Hydrogen-hydrogen bond
  • Carbon-hydrogen bond

    • What is the name of the simplest member of the alkene family?

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

    According to the IUPAC system, what is the parent structure of an alkene named?

    <p>The longest continuous chain that contains the carbon-carbon double bond</p> Signup and view all the answers

    What is the ending of the alkane name changed to when naming an alkene?

    <p>-ane to -ene</p> Signup and view all the answers

    How is the position of a double bond designated in an alkene?

    <p>By the number of the first doubly-bonded carbon</p> Signup and view all the answers

    What takes precedence over alkyl groups and halogens in determining the main carbon chain and the direction in which it is numbered?

    <p>The presence of a carbon–carbon double bond</p> Signup and view all the answers

    What is a characteristic of the physical properties of alkenes?

    <p>They are insoluble in water, but soluble in nonpolar solvents</p> Signup and view all the answers

    What is the reason for cis, trans isomerism in alkenes?

    <p>Restricted rotation about a carbon–carbon double bond</p> Signup and view all the answers

    What is the difference between cis-2-butene and trans-2-butene?

    <p>The arrangement of methyl groups and hydrogen atoms around the double bond</p> Signup and view all the answers

    Why are cis-2-butene and trans-2-butene different compounds?

    <p>Because they cannot be converted into one another at room temperature</p> Signup and view all the answers

    What is the process of converting alkyl halides into alkenes?

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

    What is the primary product when sec-Butyl chloride undergoes dehydrohalogenation?

    <p>A mixture of 1-butene and 2-butene</p> Signup and view all the answers

    What is the role of the hydroxide ion in the dehydrohalogenation mechanism?

    <p>To pull a hydrogen ion away from carbon</p> Signup and view all the answers

    What is the difference between the breaking of C-H and C-X bonds in dehydrohalogenation?

    <p>The bonds break in an unsymmetrical fashion</p> Signup and view all the answers

    What is the general formula for alcohols?

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

    What is the second method of preparing alkenes mentioned in the text?

    <p>Dehydration of alcohols</p> Signup and view all the answers

    What is required for dehydration to occur?

    <p>The presence of an acid and the application of heat</p> Signup and view all the answers

    What is the role of alumina in dehydration?

    <p>It acts as a Lewis acid</p> Signup and view all the answers

    What is a Lewis acid?

    <p>A species that accepts a pair of electrons</p> Signup and view all the answers

    What is the first step in the mechanism of dehydration of alcohols?

    <p>The union of the alcohol with a hydrogen ion</p> Signup and view all the answers

    What is lost in the second step of the dehydration mechanism?

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

    What is the final product of the dehydration mechanism?

    <p>The alkene</p> Signup and view all the answers

    What is the driving force behind the rearrangement of a carbonium ion?

    <p>The formation of a more stable carbonium ion</p> Signup and view all the answers

    What is the result of the dehalogenation of vicinal dihalides?

    <p>The formation of alkenes</p> Signup and view all the answers

    What is the type of migration where a hydrogen atom moves with a pair of electrons?

    <p>Hydride shift</p> Signup and view all the answers

    What is the outcome of the reduction of an alkyne to the double-bond stage?

    <p>The formation of either a cis-alkene or a trans-alkene</p> Signup and view all the answers

    Why does the 3,3-dimethyl-2-butyl cation rearrange to the 2,3-dimethyl-2-butyl cation?

    <p>To form a more stable carbonium ion</p> Signup and view all the answers

    Which type of carbonium ion is the most stable?

    <p>Tertiary carbonium ion</p> Signup and view all the answers

    A carbonium ion can rearrange to form a less stable carbonium ion.

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

    The dehalogenation of vicinal dihalides is a method for the synthesis of alkanes.

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

    A hydride shift is a migration of an alkyl group with a pair of electrons.

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

    Reduction of an alkyne can yield only a cis-alkene.

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

    The 2-methyl-1-butyl cation rearranges to the 2-methyl-2-butyl cation.

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

    Alkyl halides can be converted into alkanes through dehydrohalogenation.

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

    The 3,3-dimethyl-2-butyl cation rearranges to the 2,3-dimethyl-1-butyl cation.

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

    Isomeric alkenes can be formed in the dehalogenation of vicinal dihalides.

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

    Tertiary carbonium ions are less stable than primary carbonium ions.

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

    An alkyl shift is a migration of hydrogen with a pair of electrons.

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

    Study Notes

    Alkenes

    • Alkenes are unsaturated hydrocarbons with the general formula CnH2n.
    • The simplest alkene is ethylene, C2H4.
    • Alkenes have a carbon-carbon double bond, which is made up of a strong σ bond and a weak π bond.
    • The C─C distance in ethylene is less than in ethane, and the double bond is shorter than the carbon-carbon single bond.

    Names of Alkenes

    • Common names are rarely used, except for three simple alkenes: ethylene, propylene, and isobutylene.
    • Most alkenes are named by the IUPAC system.
    • The IUPAC system rules:
      • Select the longest continuous chain that contains the carbon-carbon double bond as the parent structure.
      • Indicate the position of the double bond in the parent chain by a number.
      • Carbon-carbon double bonds take precedence over alkyl groups and halogens in determining the main carbon chain and direction.

    Physical Properties

    • Alkenes possess physical properties similar to those of alkanes.
    • They are insoluble in water, but soluble in nonpolar solvents like benzene, ether, and chloroform.
    • Boiling point rises with increasing carbon number.

    Cis, Trans Isomerism

    • Alkenes show cis, trans isomerism due to restricted rotation about the carbon-carbon double bond.
    • Example: 2-butene has two stereoisomers, cis-2-butene and trans-2-butene.
    • These compounds cannot be converted into each other at room temperature and have different physical and chemical properties.

    Preparation of Alkenes

      1. Dehydrohalogenation of alkyl halides:
      • Alkyl halides are converted into alkenes by elimination of hydrogen halide.
      • Dehydrohalogenation involves removal of the halogen atom and a hydrogen atom from a carbon adjacent to the one bearing the halogen.
      1. Dehydration of alcohols:
      • Alcohols are compounds of the general formula ROH.
      • Dehydration requires the presence of an acid and heat.
      • Mechanism involves the formation of a protonated alcohol, dissociation into water and a carbonium ion, and the loss of a hydrogen ion to form the alkene.
      1. Dehalogenation of vicinal dihalides:
      • Vicinal dihalides are compounds that have halogens on adjacent carbons.
      • They are prepared by the reaction between a halogen and an alkene.
      1. Reduction of alkynes:
      • Reduction of an alkyne to the double-bond stage can yield either a cis-alkene or a trans-alkene.
      • The choice of reducing agent determines which isomer predominates, except when the triple bond is at the end of a chain.

    Studying That Suits You

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

    Quiz Team

    Related Documents

    Preparation of Alkenes PDF

    Description

    Test your knowledge of alkenes, a type of unsaturated hydrocarbon with a carbon-carbon double bond. Learn about their general formula, simplest member, and more. This quiz covers the basics of alkenes in organic chemistry.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser