Aromaticity criteria and electrophilic aromatic substitution mechanism steps and directing effects taught in a college organic chemistry sequence.
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- What does 'cyclic' mean as an aromaticity requirement?
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The molecule must contain a ring (a closed loop of atoms).- What does the 'planar' requirement mean for aromaticity?
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All ring atoms must lie in the same plane so p orbitals can align.- What does 'fully conjugated' mean for an aromatic ring?
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Every atom in the ring must have a p orbital available for overlap.- According to Huckel's rule, an aromatic ring must have ____ pi electrons.
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4n+2- How many pi electrons does benzene have?
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6 pi electrons- In Huckel's rule (4n+2) applied to benzene, what is the value of n?
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n = 1- Define an antiaromatic compound.
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A cyclic, planar, fully conjugated molecule with 4n pi electrons, which is destabilized.- Define a nonaromatic compound.
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A molecule that fails at least one aromaticity requirement, such as not being planar or not fully conjugated.- Are all carbon-carbon bond lengths in benzene the same?
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Yes, all six C-C bonds are equal in length, intermediate between single and double bonds.- What is the approximate resonance (stabilization) energy of benzene?
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About 36 kcal/mol (150 kJ/mol)- Why does benzene resist typical alkene addition reactions?
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Addition would destroy the ring's aromatic stabilization.- Why does benzene undergo substitution rather than addition with electrophiles?
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Substitution replaces a hydrogen and restores aromaticity, unlike addition which would destroy it.- What is the first step of the electrophilic aromatic substitution mechanism?
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The electrophile attacks the ring, forming a resonance-stabilized carbocation called the arenium ion.- What is another name for the arenium ion intermediate in EAS?
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The sigma complex- What hybridization does the carbon attacked by the electrophile have in the arenium ion?
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