Chapter17

Chapter17

• 1.
  Chapter 17 Spring2009
• 2.
  Benzene Six-membered ringIs planar All C-C bond lengths are equal Kekulé structure Resonance description of benzene Implication of the geometry of the structure above Shorter isolated double bonds Longer single bonds Common representation of benzene
• 3.
  Benzene Benzene isthe parent aromatic molecule. Benzene has the following characteristics that are common among all aromatic compounds Benzene is cyclic and conjugated Benzene is unusually stable in comparison to a molecule with three isolated pi bonds Benzene is planar and has the shape of a regular hexagon. All bond angles are 120º, all carbon atoms are sp 2 hybridized, and all carbon-carbon bond lengths are intermediate in length between a single and double bond. Benzene undergoes substitution reactions rather than electrophilic addition reactions that would destroy its conjugation.
• 4.
  Larger aromatic hydrocarbonshttp://www.cem.msu.edu/~reusch/VirtualText/react3.htm
• 5.
  Pictures of BenzeneElectrostatic potential surface Benzene molecular orbital In top picture notice a p orbital on each C atom. Bottom picture show the overlap of the p orbitals.
• 6.
  Orbital picture ofbenzene each carbon atom is sp 2 hybridized The resonance picture indicates why each C-C bond is the same length.
• 7.
  Electrostatic potential surfaceElectron-rich portion represents π electron cloud
• 8.
  For a compoundto be classified as aromatic, it must fulfill both of the of the following criteria: It must have an uninterrupted cyclic cloud of π electrons above and below the plane of the molecule (this is often called the π cloud. Also, the π cloud must be cyclic , uninterrupted , and planar . The p cloud must contain an odd number of pairs of π electrons. (4n+2 rule)
• 9.
  Common names foraromatic compounds
• 10.
  IUPAC names Toname benzene ring with one substituent, name the substituent and add the word benzene. ethyl benzene ?
• 11.
  If the alkanechain is longer than six carbon atoms name the benzene ring as a phenyl substituent.
• 12.
  Benzyl Benzyl substituent
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  Disubstituted benzenes 1,2-dimethylbenzene 1,3-dimethylbenzene 1,4-dimethylbenzene IUPAC names
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  Same substituent meta-dichlorobenzeneor, 1,3-dichlorobenzene
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  Different substituents Thesetwo have common root names
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  Different substituents Thesetwo have common root names toluene analine
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  Different substituents Thesetwo have common root names meta-chlorotoluene ortho-chloroanaline
• 18.
  Different substituents Thesedon’t have a common root name so alphabetize the name of the substituents.
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  Different substituents Thesedon’t have a common root name so alphabetize the name of the substituents. ortho-bromochlorobenzene para-bromonitrobenzene
• 20.
  Heat of hydrogenationdata The low heat of hydrogenation means that benzene is especially stable – this extra stability is characteristic of all aromatic compounds.
• 21.
  Reaction of aromaticcompounds Benzene does not undergo addition reactions typical of other unsaturated hydrocarbons.
• 22.
  What makes acompound aromatic? A molecule must be cyclic Planar Completely conjugated (alternating single-double bonds) Have a particular number of π electrons
• 23.
  This molecule isnon-aromatic It is cyclic, completely conjugated, non-planar, and contains 8 π electrons
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  This molecule isanti-aromatic Cyclic, planar, completely conjugated, and contain four π electrons.
• 25.
  Aromatic, anti-aromatic, ornon-aromatic Aromatic: A cyclic planar, completely conjugated compound with 4n+2 π electrons Anti-aromatic: A cyclic, planar, completely conjugated compound with 4n π electrons Non-aromatic: A compound that lack one (or more) of the following requirements for aromaticity.
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  Aromatic compounds canhave more than one ring.
• 27.
  Aromatic rings cancontain a single ring with lots of alternating single-double bonds
• 28.
  atomic orbitals molecularorbitals
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  Anti-aromatic
• 30.
  The inscribed polygonmethod Draw the polygon in question inside a circle with its vertices touching the circle and one of the vertices pointing down. Mark the points at which the polygon intersects the circle. Draw a line horizontally through the center of the circle and label MOs as bonding, nonbonding, or antibonding. Add the electrons, beginning with the lowest energy MO.
• 31.
  Label the cation,radical, and anion as aromatic, antiaromatic, or nonaromatic.
• 32.
  Heterocyclic aromatic compounds
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• 34.
  Nucleic acids
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  Thymine
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• 37.
  Aromatic Question Thiamin,or vitamin B1, contains a five-membered, nitrogen-sulfur heterocycle called a thiazalium ring. Explain why the thiazolium ring is aromatic.
• 38.
  Cycloheptatrienyl cation, radicaland anion problem
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