Hydrocarbons and Halogenoalkanes

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Anonymous
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211580
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Hydrocarbons and Halogenoalkanes
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2013-04-05 10:49:11
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Chemistry
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Advanced Higher Chemistry - Unit Three - Hydrocarbons and Halogenoalkanes
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  1. What is a sigma bond?
    A sigma bond is a covalent bond formed by the end-on overlap of two atomic orbitals lying along the axis of the bond
  2. What is a pi bond?
    A pi bond is a covalent bond formed by the sideways overlap of two parallel atomic orbitals lyingperpendicular to the axis of the bond
  3. Which are stronger, pi bonds or sigma bonds?
    Sigma bonds (as the end-on overlap is much moreefficient than side-on overlap)
  4. What is hybridisation?
    The process of mixing atomic orbitals in an atom to generate a set of new atomic orbitals called hybrid orbitals
  5. What is sp3 bonding? And what type of hydrocarbons is it found in?
    • sp3 bonding is when the three 2p orbitals and one 2s orbital mix to form degenerate hybrid orbitals
    • Alkanes
  6. What is sp2 bonding? And what type of hydrocarbons is it found in?
    • sp2 bonding is when the 2s orbital and two 2p orbitals mix to form hybrid orbitals
    • Alkenes
  7. Alliances undergo substitution reactions with chlorine and bromine by a _______ _________ mechanism?
    chain reaction
  8. What are the three stages in a chain reaction?
    • Initiation
    • Propagation
    • Termination
  9. What happens in the initiation step if methane is reacted with Cl?
    Ultraviolet light provides energy for the reaction to start. Homolytic fission of Cl or Br occurs. This creates free radicals (atoms or groups or atoms with an unpaired electron) which are highly reactive.
  10. What happens in the propagation step?
    • Each chlorine radical that is produced goes on to attack a methane molecule removing a hydrogen atom from it to form HCl and a methyl radical: Cl+ CH---> HCl + CH3.
    • The methyl radical then attacks a chlorine molecule to form chloromethane and another chlorine radical: CH3. + Cl---> CH3Cl + Cl.
    • In each of the propagation steps one radicalsenders the reaction and another radical is generated . These steps sustain the reaction.
  11. What happens in the termination step?
    • Reactions in which radicals are used up and noT regenerated eg 
    • CH3+ Cl. ---> CH3Cl
    • CH3+ CH3---> CH3CH3
    • Cl. + Cl---> Cl2
  12. How can alkenes be prepared in the lab?
    • Dehydration of alcohols
    • Base-induced elimination of hydrogen halides from monohalogenoalkanes
  13. How are alcohols dehydrated in the lab?
    By passing them over hot aluminium chloride or using concentrated sulphuric acid or orthophosphoric acid
  14. Alkenes undergo addition reactions with hydrogen to form...?
    Alkanes
  15. Alkenes undergo addition reactions with halogens to form...?
    Dihaloalkanes
  16. Alkenes undergo addition reactions with hydrogen halides to form...?
    Monohalogenoalkanes
  17. Alkenes undergo addition reactions with water to form...?
    Alcohols
  18. The addition reaction of an alkene with hydrogen is also known as...? What is it catalysed by?
    • Hydrogenation
    • Nickel or platinum
  19. The addition reaction of an alkene with a halogen is also known as...?
    Halogenation
  20. The addition reaction of an alkene with hydrogen halide is also known as...?
    Hydrohalogenation
  21. The addition reaction of an alkene with water is also known as...? What is it catalysed by?
    • Hydration
    • Acid
  22. What is Markovnikov's rule?
    Marokovinikov's rule states that when H-X or H-OH adds onto an unsymmetrical Allende the major product is the one in which the H atom ends up attached to the carbon atom of the double bond which already has the greater number of hydrogen atoms bonded to it
  23. What type of intermediate is involved in the mechanisms in the of the following reactions:
    Halogenation?
    Hydrohalogenation?
    Acid-catalysed hydration?
    • A cyclic ion intermediate
    • A carbocation intermediate
    • A carbocation intermediate
  24. What is the difference between a primary, secondary and tertiary monohalogenoalkane?
    • Primary - halogen atom on carbon attached to 1 other carbon atom
    • Secondary - halogen atom on carbon attached to 2 carbon atoms
    • Tertiary - halogen atom on carbon attached to 3 carbon atoms
  25. What is the main reaction of monohalogenoalkanes?
    Nucleophilic substitution
  26. Monohalogenoalkanes undergo elimination reactions to form...?
    Alkenes
  27. Monohalogenoalkanes react with alkalis to form...?
    Alcohols
  28. Monohalogenoalkanes react with alcoholic alkoxides to form...?
    Ethers
  29. Monohalogenoalkanes react with ethanolic cyanides to form...?
    Nitriles (which can be hydrolysed to carboxylic acids)
  30. Monohalogenoalkanes react with ammonia to form...?
    Amines

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