The Unusual Reactivity and Stability of Benzene

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Questions and Answers

Which of the following is a characteristic of aromatic compounds?

  • They are not cyclic
  • They have a low heat of hydrogenation (correct)
  • They undergo addition reactions typical of other highly unsaturated compounds
  • They do not contain p orbitals

According to Hückel's rule, how many π electrons are required for a compound to be aromatic?

  • 2
  • 4
  • 6 (correct)
  • 8

Which of the following compounds is antiaromatic?

  • Cyclooctatetraene
  • Cyclobutadiene (correct)
  • Cyclopentadiene
  • Benzene

Which of the following compounds satisfies all the criteria for aromaticity?

<p>Benzene (A)</p> Signup and view all the answers

Which of the following compounds is not aromatic?

<p>Cyclooctatetraene (A)</p> Signup and view all the answers

How many π electrons are required for a completely conjugated, planar, 8-membered ring to be aromatic?

<p>14 (C)</p> Signup and view all the answers

Which of the following compounds is NOT considered aromatic?

<p>Cyclopentadiene (C)</p> Signup and view all the answers

How many pi electrons are present in the pyrimidine-derived DNA base cytosine?

<p>6 (D)</p> Signup and view all the answers

Which of the following statements about molecular orbital (MO) theory is correct?

<p>MO theory explains bonding in aromatic compounds. (A)</p> Signup and view all the answers

What is the basis of Hückel's rule?

<p>The number of electrons in the compound. (B)</p> Signup and view all the answers

Which of the following compounds is considered fully conjugated and aromatic?

<p>Pyrrole (D)</p> Signup and view all the answers

In pyridine, where is the nonbonded electron pair localized?

<p>On the nitrogen atom (C)</p> Signup and view all the answers

Which of the following statements about benzene is true?

<p>Benzene has four degrees of unsaturation. (C)</p> Signup and view all the answers

What is the result of benzene reacting with bromine in the presence of a Lewis acid?

<p>Substitution reaction (C)</p> Signup and view all the answers

What did August Kekulé propose about the structure of benzene?

<p>Benzene contains a six-membered ring with alternating single and double bonds. (A)</p> Signup and view all the answers

What is the basis for current descriptions of benzene?

<p>Resonance and electron delocalization (D)</p> Signup and view all the answers

What must any structure for benzene account for?

<p>It contains a six-membered ring and three additional degrees of unsaturation. (C)</p> Signup and view all the answers

True or False: Benzene is a highly reactive hydrocarbon.

<p>False (B)</p> Signup and view all the answers

Which of the following best describes the bond lengths in benzene?

<p>Benzene has three short double bonds alternating with three longer single bonds (A)</p> Signup and view all the answers

Which of the following statements about the resonance description of benzene is true?

<p>The true structure of benzene is a hybrid of two Lewis structures (C)</p> Signup and view all the answers

Which of the following correctly describes the number of π electrons in benzene?

<p>Benzene has six π electrons (B)</p> Signup and view all the answers

Which of the following statements about the actual bond length in benzene is true?

<p>The actual bond length in benzene is shorter than the carbon–carbon single bond (D)</p> Signup and view all the answers

Which of the following statements about the electron density in benzene is true?

<p>The electron density in benzene is evenly distributed throughout the molecule (C)</p> Signup and view all the answers

Which of the following statements about naming substituted benzenes is true?

<p>To name a benzene ring with one substituent, you need to name the substituent and add the word benzene (A)</p> Signup and view all the answers

Which statement best describes the molecular orbitals of benzene?

<p>There are 6 pi molecular orbitals formed by the combination of 6 atomic p orbitals. (A)</p> Signup and view all the answers

Which of the following is NOT a characteristic of the molecular orbitals of benzene?

<p>The larger the number of nodes, the higher in energy the MO. (A)</p> Signup and view all the answers

What is the inscribed polygon method used for?

<p>Determining the aromaticity of monocyclic completely conjugated systems. (B)</p> Signup and view all the answers

What is the relationship between the number of MOs and the number of vertices in the inscribed polygon method?

<p>The number of MOs is always equal to the number of vertices of the polygon. (C)</p> Signup and view all the answers

Which statement best describes pi stacking?

<p>All of the above (D)</p> Signup and view all the answers

What is the purpose of the inscribed polygon method in predicting aromaticity?

<p>To determine the aromaticity of a monocyclic completely conjugated system. (B)</p> Signup and view all the answers

According to the text, what is the basis for the current description of benzene?

<p>Resonance and electron delocalization (A)</p> Signup and view all the answers

What did August Kekulé propose about the structure of benzene?

<p>It is a rapidly equilibrating mixture of two compounds with alternating bonds (A)</p> Signup and view all the answers

Which of the following compounds is considered fully conjugated and aromatic?

<p>Benzene (B)</p> Signup and view all the answers

According to Hückel's rule, how many π electrons are required for a compound to be aromatic?

<p>4n+2 (D)</p> Signup and view all the answers

Which of the following compounds satisfies all the criteria for aromaticity?

<p>Benzene (C)</p> Signup and view all the answers

What is the result of benzene reacting with bromine in the presence of a Lewis acid?

<p>Substitution (A)</p> Signup and view all the answers

Which of the following is true about the bond lengths in benzene?

<p>All bond lengths are equal (A)</p> Signup and view all the answers

What is the true structure of benzene?

<p>A resonance hybrid of two equivalent Lewis structures (D)</p> Signup and view all the answers

How many π electrons does benzene have?

<p>6 (A)</p> Signup and view all the answers

What is the actual bond length in benzene?

<p>Intermediate between a carbon-carbon single bond and a carbon-carbon double bond (A)</p> Signup and view all the answers

How many atoms surround each carbon atom in a benzene ring?

<p>3 (D)</p> Signup and view all the answers

What is a benzene substituent called?

<p>Phenyl group (A)</p> Signup and view all the answers

Which of the following is true about the molecular orbitals of benzene?

<p>There are six pi molecular orbitals (B)</p> Signup and view all the answers

What is the lowest energy bonding molecular orbital in benzene?

<p>Ψ1 (B)</p> Signup and view all the answers

Which of the following statements about the inscribed polygon method is true?

<p>It works for all monocyclic completely conjugated systems (B)</p> Signup and view all the answers

What is the highest occupied molecular orbital in benzene called?

<p>HOMO (C)</p> Signup and view all the answers

What is the lowest unoccupied molecular orbital in benzene called?

<p>LUMO (C)</p> Signup and view all the answers

Which of the following is a characteristic of aromatic compounds?

<p>They have a lower energy compared to non-aromatic compounds (C)</p> Signup and view all the answers

Which of the following compounds satisfies all the criteria for aromaticity?

<p>Benzene (C)</p> Signup and view all the answers

What is the result of benzene reacting with bromine in the presence of a Lewis acid?

<p>Substitution product (B)</p> Signup and view all the answers

How many π electrons are required for a completely conjugated, planar, 8-membered ring to be aromatic?

<p>10 (A)</p> Signup and view all the answers

Which of the following compounds is antiaromatic?

<p>Cyclobutadiene (C)</p> Signup and view all the answers

Which of the following compounds is NOT considered aromatic?

<p>Cyclobutadiene (D)</p> Signup and view all the answers

What must any structure for benzene account for?

<p>All of the above (D)</p> Signup and view all the answers

Which of the following compounds is NOT considered aromatic?

<p>Cyclopentadiene (D)</p> Signup and view all the answers

In pyridine, where is the nonbonded electron pair localized?

<p>On the nitrogen atom (A)</p> Signup and view all the answers

Which of the following compounds satisfies all the criteria for aromaticity?

<p>Tropylium cation (C)</p> Signup and view all the answers

What is the relationship between the number of MOs and the number of vertices in the inscribed polygon method?

<p>The number of MOs is equal to the number of vertices minus one (B)</p> Signup and view all the answers

Which of the following compounds is not aromatic?

<p>Thiophene (B)</p> Signup and view all the answers

What must any structure for benzene account for?

<p>The presence of six pi electrons (D)</p> Signup and view all the answers

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