Aromaticity

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| By Ochem_ownsmylife
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Aromaticity - Quiz

Determining aromaticity, non aromatics, and anti-aromatics.


Questions and Answers
  • 1. 

    Why is there a huge gain in the stability of benzene's double bonds compared to cyclohexene?

    • A.

      Cyclic congugation increases the number of p orbital interactions in the conjugated system, stabilizing the pi bonds. Cyclohexene lacks this stability, and the energy of its pi bond is greater (less stable).

    • B.

      The linear conjugation of the cyclohexene makes it less stable.

    • C.

      Cyclic congugation increases the number of p orbital interactions in the conjugated system, stabilizing the pi bonds. Cyclohexene has only linear delocalized pi electrons.

    Correct Answer
    A. Cyclic congugation increases the number of p orbital interactions in the conjugated system, stabilizing the pi bonds. Cyclohexene lacks this stability, and the energy of its pi bond is greater (less stable).
    Explanation
    C is incorrect because the pi bonds in the cyclohexene are localized, not delocalized.

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  • 2. 

    Choose the answer that best fills in the blanks of the following statement:An aromatic must have _____________ of pi electrons, above and below the _____ of the molecule. This cloud must have an ________ of electon pairs.

    • A.

      A uniform cloud, plane, even number

    • B.

      An uninterrupted cyclic cloud, plane, odd number

    • C.

      A high energy cloud, most polar region, odd number

    Correct Answer
    B. An uninterrupted cyclic cloud, plane, odd number
    Explanation
    An aromatic compound is characterized by an uninterrupted cyclic cloud of pi electrons, which is spread above and below the plane of the molecule. This cloud must have an odd number of electron pairs. This description aligns with the concept of aromaticity, where the delocalized pi electrons form a stable and continuous ring of electron density. The requirement for an odd number of electron pairs is a result of the Huckel's rule, which states that aromatic compounds must have 4n+2 pi electrons, where n is an integer.

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  • 3. 

    [10]-annulene is not an aromatic compound becuase it is not ________. This causes it to be classified as a ____-aromatic. (separate answers with a comma)

    Correct Answer
    planar, non
    Explanation
    Annulenes are cyclic compounds with alternating single and double bonds. In order to be aromatic, a molecule must fulfill certain criteria, one of which is planarity. A planar molecule has all its atoms lying in the same plane. However, [10]-annulene is not planar due to the strain caused by the high angle between the double bonds. As a result, it cannot exhibit aromaticity and is classified as non-aromatic.

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  • 4. 

    Why would a compound be anti-aromatic?

    • A.

      If a compound has a 4n number of pi electrons, it will be anti-aromatic.

    • B.

      If a compound fits Huckel's Rule.

    • C.

      If a compound cannot escape being planar and has 4n number of pi electrons.

    • D.

      If a compound has an odd number of atoms in its ring structure.

    Correct Answer
    C. If a compound cannot escape being planar and has 4n number of pi electrons.
    Explanation
    If a compound cannot escape being planar and has 4n number of pi electrons, it will be anti-aromatic. This is because anti-aromatic compounds have a cyclic structure with conjugated pi bonds, but unlike aromatic compounds, they have a high energy due to destabilization caused by the electron delocalization. The requirement for the compound to be planar is necessary for the delocalization of the pi electrons. Additionally, the 4n number of pi electrons ensures that the compound follows Huckel's rule, which states that aromatic compounds have 4n+2 pi electrons, while anti-aromatic compounds have 4n pi electrons.

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  • 5. 

    Recall pyridine:What is a heterocycle? Is pyridine an aromatic?

    • A.

      Any cyclic molecule with an electronegative atom in it. Pyridine is not an aromatic.

    • B.

      Any cyclic molecule with a nitrogen in it. Pyridine is an aromatic

    • C.

      Any cyclic molecule with a non carbon in it. Pyridine is an aromatic

    • D.

      Any cyclic molecule with an electronegative atom in it. Pyridine is an aromatic

    • E.

      Any cyclic molecule with a non carbon in it. Pyridine is not an aromatic

    Correct Answer
    C. Any cyclic molecule with a non carbon in it. Pyridine is an aromatic
    Explanation
    The correct answer is "Any cyclic molecule with a non carbon in it. Pyridine is an aromatic." This is because pyridine is a heterocycle, which means it contains a non-carbon atom in its ring structure. In the case of pyridine, it has a nitrogen atom in its ring, making it a heterocycle. Additionally, pyridine is also considered aromatic because it follows the criteria for aromaticity, such as having a planar structure, a conjugated system of pi electrons, and meeting the Huckel's rule of 4n+2 pi electrons.

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  • 6. 

    Which of the following are aromatic? Cyclopropene, Cyclopropenyl cation, Cycloheptatrienly cation, Cycloheptatrenyl anion?

    • A.

      Cyclopropenyl cation, Cycloheptatrienly cation

    • B.

      Cyclopropene, Cycloheptatrienly cation, Cycloheptatrenyl anion

    • C.

      Cyclopropenyl cation

    • D.

      Cyclopropene, Cyclopropenyl cation, Cycloheptatrienly cation, Cycloheptatrenyl anion

    Correct Answer
    A. Cyclopropenyl cation, Cycloheptatrienly cation
    Explanation
    The correct answer is Cyclopropenyl cation, Cycloheptatrienly cation. Both of these compounds have a conjugated system of pi electrons, which satisfies the criteria for aromaticity. Aromatic compounds are characterized by having a cyclic structure, a planar arrangement of atoms, and a continuous ring of pi electrons in a conjugated system. Cyclopropenyl cation has a three-membered ring with two pi electrons, while Cycloheptatrienly cation has a seven-membered ring with six pi electrons.

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  • Current Version
  • Mar 22, 2023
    Quiz Edited by
    ProProfs Editorial Team
  • Nov 22, 2009
    Quiz Created by
    Ochem_ownsmylife
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