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Annulene quiz

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  • What is an annulene in organic chemistry?
    An annulene is a monocyclic compound with alternating single and double bonds, named by the number of carbons in the ring followed by 'annulene.'
  • How is benzene classified in terms of annulenes?
    Benzene is a 6-annulene because it has six carbons in a ring with alternating single and double bonds.
  • Why do larger annulenes tend to be non-planar?
    Larger annulenes become non-planar due to bond strain, which prevents them from maintaining a flat, planar structure.
  • What shape does cyclooctatetraene (8-annulene) typically adopt and why?
    Cyclooctatetraene adopts a non-planar 'taco' shape to avoid antiaromaticity, making it non-aromatic.
  • What happens to cyclooctatetraene when it gains two negative charges?
    When cyclooctatetraene becomes an 8-annulenedianion, it flattens out, becomes planar, and is aromatic due to having 10 pi electrons.
  • What is Huckel's rule for aromaticity?
    Huckel's rule states that a planar, cyclic molecule is aromatic if it has 4n+2 pi electrons, where n is a non-negative integer.
  • What is the aromaticity of a planar 8-annulene?
    A planar 8-annulene would be antiaromatic, but it avoids this by folding and becoming non-aromatic.
  • How does the number of carbons in an annulene affect its planarity and aromaticity?
    Annulenes with 9 carbons or fewer can be planar and aromatic if they have a Huckel's rule number of pi electrons; those with 10 or more carbons are usually non-planar and non-aromatic due to strain.
  • What happens to annulenes with 8 or more carbons and a non-Huckel number of pi electrons?
    They fold to avoid antiaromaticity and become non-aromatic.
  • Why are annulenes with 7 or fewer carbons antiaromatic if they have a non-Huckel number of pi electrons?
    They are too small to fold, so they remain planar and are forced to be antiaromatic.
  • What is meant by an 'all-cis' annulene?
    An all-cis annulene has all double bonds with adjacent single bonds oriented toward the inside of the ring.
  • Why might the rules for annulene aromaticity differ between professors?
    Some professors may use advanced techniques like x-ray crystallography to determine planarity, leading to different interpretations of aromaticity.
  • What motivates an annulene to become planar and aromatic?
    Annulenes are motivated to become planar and aromatic if they have a Huckel's rule number of pi electrons because aromaticity provides extra stability.
  • What should you do if your professor's rules for annulene aromaticity differ from textbook rules?
    You should follow your professor's guidelines, as they determine your grading.
  • What is the general trend for planarity in annulenes with increasing ring size?
    As ring size increases, annulenes are more likely to become non-planar due to increased bond strain.