Chapter 167 through 1611 Aromatic Compounds

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Chapter 16-7 through 16-11Aromatic Compounds
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Cyclopentadienyl ions
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Cyclopentadienyl Ions

• The cation has an empty p orbital, 4 electrons,
  so antiaromatic.
• The anion has a nonbonding pair of electrons in a
  p orbital, 6 e-s, aromatic.

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Acidity of Cyclopentadiene

• pKa of cyclopentadiene is 16, much more acidic
  than other hydrocarbons.

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Tropylium Ion

• The cycloheptatrienyl cation has 6 pi electrons
  and an empty p orbital.
• Aromatic more stable than open chain ion

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Dianion of 8Annulene

• Cyclooctatetraene easily forms a -2 ion.
• Ten electrons, continuous overlapping p orbitals,
  so it is aromatic.
  

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Pyridine

• Heterocyclic aromatic compound.
• Nonbonding pair of electrons in sp2 orbital, so
  weak base, pKb 8.8.

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Pyrrole

• Also aromatic, but lone pair of electrons is
  delocalized, so much weaker base.

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Basic or Nonbasic?
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Other Heterocyclics
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Fused Ring Hydrocarbons

• Naphthalene

• Anthracene

• Phenanthrene

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Large Polyaromatic Hydrocarbons (PAHs)
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Fused Heterocyclic Compounds

• Common in nature, synthesized for drugs.

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Allotropes of Carbon

• Amorphous small particles of graphite charcoal,
  soot, coal, carbon black.
• Diamond a lattice of tetrahedral Cs.
• Graphite layers of fused aromatic rings.

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Some New Allotropes

• Fullerenes 5- and 6-membered rings arranged to
  form a soccer ball structure.
• Nanotubes half of a C60 sphere fused to a
  cylinder of fused aromatic rings.

1991 Molecule of the Year by Science
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IUPAC name for C60

• Hentriacontacyclo29.29.0.0.2,14.03,12.
  04,59.05,10.06,58. 07,55.08,53.09,21.
  011,20.013,18.015,30. 016,28.017,25.019,24.022,52.
  023.50.026,49.027,47. 029,45.032,44.033,60.
  034,57.035,43.036,56. 037,41.038,54.039,51.
  040,48.042,46hexaconta-1,3,5(10),6,8,11,13(18),
  14,16,19,21,23,25,27,29(45),30,32(44),33,35(43),
  36,38(54),39(51),40(48),41,46,49,52,55,57,59-triac
  ontaene

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The Nobel Prize in Chemistry 1996
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(No Transcript)
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Proof for C60s Soccer Ball structure
X-ray crystal structure of (C60)OsO44-tert-butylpy
ridine) Note The carbon atoms are green,
hydrogen atoms are white, nitrogen atoms are dark
blue, osmium atom is magenta, and oxygen atoms
are red in the ball-and-stick representation.
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Proof for C70s Rugby Ball structure
X-ray crystal structure of (C70)Ir(CO)(Cl)(PPh3)3
) .Note The carbon atoms are green, chlorine
atom is yellow, hydrogen atoms are white, iridium
atom is light blue, oxygen atom is red, and
phosphorus atoms are magneta in the
ball-and-stick representation.
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Nanotubes
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Nanotubes
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Aromaticity exercises
Acidity of Aromatic compounds
Aromatic vs. Antiaromatic
Heterocycle aromatics
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Quiz
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Quiz

• Show which nitrogen atom(s) in purine is/are
  basic, and which one(s) is/are not basic.

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Why would the reaction below proceed at an
extremely slow rate, if at all?
The cyclopentadienyl cation intermediate would be
anti-aromatic!
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Draw the product (A) of the following Diels-Alder
reaction. A is a key intermediate in the
synthesis of the addicting pain reliever
morphine, isolated form the opium poppy.
The Opium Poppy
What is A?
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A
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Opium continued. . .
such a good dienophile?
Why is
It has a carbonyl adjacent to the double bond to
make it electron poor.
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Youll think Im making these compounds up, but
theyre real. The following reactions have been
used to synthesize dieldrin and aldrin (named for
Diels and Alder), two pesticides having a similar
story to DDT. Identify X, Y, and Z in the
reaction scheme.
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For Next Time

• Read the rest of chapter (except for
• 16-14). Do end-of-chapter problems.