Chapter 11 Arenes

Question 0

benzene

Answer 0

• does not react with Br2 via elimination
• reacts with substitution in the presence of FeBr3 (C6H5Br)
• all hydrogens are equivalent
• planar, all bonds are sp2 hybridized and angles are 120 degrees

Question 1

arene

Answer 1

-hydrocarbon based on the benzene ring as a structural unit

Question 2

hydrogenation of benzene

Answer 2

-needs 3 moles of H2 (3H2) and rhodium or platinum at room temp to form cyclohexane

Question 3

heats of hydrogentation

Answer 3

-conjugation that is cyclic has a lower than expected heat of hydrogenation, which infers that benzene is more stable than an open triene

Question 4

benzene MO

Answer 4

• 3 = bonds
• 6 C atoms
• 6 p orbitals
  
  • 3 bonding
  • 3 antibonding

Question 5

phenyl

Answer 5

• when benzene ring is considered as a substituent, this is its name
• abbreviated by Ph or O with line through the middle

Question 6

benzyl group

Answer 6

• benzene ring is substituent with CH2

ex. C6H5CH2-

Question 7

polycyclic aromatic hydrocarbons (PAHs)

Answer 7

• multiple benzene rings fused together
• cannot spin; rigid
• not water soluble
• very volatile
• increased toxicity with greater number of benzene rings

Question 8

poly chloro biphenyl (PCBs)

Answer 8

• can have up to 10 substituents on the biphenyl

- can spin about the single bond

Question 9

physical properties of benzene

Answer 9

• nonpolar
• insoluble in water
• less dense than water

Question 10

benzylic carbon

Answer 10

-a carbon atom that is directly attached to a benzene ring

Question 11

benzylic carbocations and radicals

Answer 11

-more highly stabilized than allylic carbocations/radicals (H2C=CH-)

Question 12

benzylic radical

Answer 12

-more stable than allylic radical because the C-H bond is easier to break and has a lower value of enthalpy
(mechanism is free-radical chlorination)

Question 13

chlorination of toulene

Answer 13

• takes place exclusively at the benzylic carbon (the carbon attached to the benzene ring)
• the benzylic hydrogen is abstracted and replaced by a Cl atom

Question 14

oxidation of benzene

Answer 14

• Na2Cr2O7 (sodium dichromate) does not react with benzene unless it is substituted
• Na2Cr2O7 and KMnO4 are both strong oxidizing agents
• compounds must have a benzylic H to spontaneously combust
• CO2H (carboxylic acids) are the highest oxidation state possible