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?
- The molecule must contain a ring (a closed loop of atoms).
- What does the 'planar' requirement mean for aromaticity?
- All ring atoms must lie in the same plane so p orbitals can align.
- What does 'fully conjugated' mean for an aromatic ring?
- 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.
- 4n+2
- How many pi electrons does benzene have?
- 6 pi electrons
- In Huckel's rule (4n+2) applied to benzene, what is the value of n?
- n = 1
- Define an antiaromatic compound.
- A cyclic, planar, fully conjugated molecule with 4n pi electrons, which is destabilized.
- Define a nonaromatic compound.
- 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?
- 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?
- About 36 kcal/mol (150 kJ/mol)
- Why does benzene resist typical alkene addition reactions?
- Addition would destroy the ring's aromatic stabilization.
- Why does benzene undergo substitution rather than addition with electrophiles?
- Substitution replaces a hydrogen and restores aromaticity, unlike addition which would destroy it.
- What is the first step of the electrophilic aromatic substitution mechanism?
- 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?
- The sigma complex
- What hybridization does the carbon attacked by the electrophile have in the arenium ion?
- sp3