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22 Cards in this Set
- Front
- Back
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aliphatic compound
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An organic compound that is not aromatic.
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annulenes
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Cyclic hydrocarbons with alternating single and double bonds. [6]annulene is also known as benzene.
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antiaromatic compound
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A compound that has a continuous ring of p orbitals as in an aromatic compound, but delocalization of the pi electrons over the ring increases the electronic energy. In most cases, the structure must be planaer (or nearly planar) and have (4N) pi electrons, with N an integer.
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aromatic compound
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A cyclic compound containing some number of conjugated double bonds, characterized by an unusually large resonance energy. Aromatics generally have 4N + 2 pi electrons, with N an integer. Delocalization of the pi electrons over the ring results in the lowering of electronic energy.
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aryl group (abbreviated Ar)
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The aromatic group that remains after the removal of a hydrogen from an aromatic ring; the aromatic equivalent of the generic alkyl group (R).
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benzenoid band
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The weak band around 250 to 270 nm in the UV spectra of benzenoid aromatics. This band is usually characterized by multiple, sharper absorptions (fine structure).
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benzyl group (Ph-CH2-)
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The seven-carbon unit consisting of a benzene ring and a methylene group.
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degenerate orbitals
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Orbitals having the same energy.
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fused rings
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Rings that share a common carbon-carbon bond together with its two carbon atoms.
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heterocycle
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A cyclic compound in which one or more of the ring atoms is not carbon.
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aromatic heterocycle
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A heterocyclic compound that fulfills the criteria for aromaticity and that has a substantial resonance energy.
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Huckel's rule
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A cyclic molecule or ion that has a continuous ring of overlapping p orbitals will be: 1. Aromatic if the number of pi electrons is 4N + 2. 2. Antiaromatic is the number of pi electrons is 4N.
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Kekule structure
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A classical structural formula for an aromatic compound, showing localized double bonds.
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nonaromatic compound
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Neither aromatic nor antiaromatic; lacking the continuous ring of overlapping p orbitals required for aromaticity or antiaromaticity.
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ortho
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Having a 1,2-relationship on a benzene ring.
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meta
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Having a 1,3-relationship on a benzene ring.
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para
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Having a 1,4-relationship on a benzene ring.
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phenyl group (Ph or phi)
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The benzene ring, minus one hydrogen atom, when named as a substituent on another molecule.
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polygon rule
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The energy diagram of the MO's of a regular, completely conjugated cyclic system has the same polygonal shape as the compound, with one vertex (the all-bonding MO) at the bottom. The nonbonding line cuts horizontally through the center of the polygon.
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polynuclear aromatic compounds
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Aromatic compound composed of two or more fused aromatic rings. Naphthalene is an example of a polynuclear aromatic hydrocarbon (PAH or PNA), and indole is an example of a polynuclear aromatic heterocycle.
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resonance energy
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The extra stabilization provided by delocalization, compared with a localized structure. For aromatic compounds, the resonance energy is the extra stabilization provided by the delocalization of the electrons in the aromatic ring.
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tropylium ion
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The cycloheptatrienyl cation.
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