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Zorluk: ZorBenzene Structure, Aromaticity, and Electrophilic Substitution

In electrophilic aromatic substitution, benzene reacts with strong electrophiles generated by specific catalyst-reagent combinations. Match each benzene reaction system on the left with its corresponding active electrophile species generated during the reaction mechanism on the right.

  • Nitration using concentrated HNO3\text{HNO}_3 and concentrated H2SO4\text{H}_2\text{SO}_4Nitronium ion (NO2+\text{NO}_2^+)
  • Friedel-Crafts acylation using ethanoyl chloride (CH3COCl\text{CH}_3\text{COCl}) and anhydrous AlCl3\text{AlCl}_3Acylium ion (CH3C+=O\text{CH}_3\text{C}^+=\text{O})
  • Catalytic bromination using Br2\text{Br}_2 and FeBr3\text{FeBr}_3Bromonium ion / Polarized bromine complex (Br+\text{Br}^+)
  • Sulfonation using fuming or concentrated H2SO4\text{H}_2\text{SO}_4Neutral sulfur trioxide (SO3\text{SO}_3)

Cevap

Nitration produces the nitronium ion (NO2+\text{NO}_2^+); Friedel-Crafts acylation generates the acylium ion (CH3C+=O\text{CH}_3\text{C}^+=\text{O}); Catalytic bromination produces the bromonium ion (Br+\text{Br}^+); Sulfonation generates neutral sulfur trioxide (SO3\text{SO}_3).
Each benzene electrophilic substitution reaction relies on a specific reagent and catalyst mechanism to create a powerful electrophile capable of disrupting benzene's stable aromatic system. Nitration generates NO2+\text{NO}_2^+ via acid-base protonation of nitric acid by sulfuric acid. Friedel-Crafts acylation forms the acylium ion CH3C+=O\text{CH}_3\text{C}^+=\text{O} through chloride abstraction by the Lewis acid AlCl3\text{AlCl}_3. Bromination generates a polarized Br+\text{Br}^+ complex using FeBr3\text{FeBr}_3. Sulfonation relies on SO3\text{SO}_3, which features an electron-deficient sulfur atom due to polar S=O bonds.

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1
Identify the electrophile in nitration
Concentrated H2SO4\text{H}_2\text{SO}_4 acts as an acid to protonate HNO3\text{HNO}_3. Loss of H2O\text{H}_2\text{O} yields NO2+\text{NO}_2^+ (nitronium ion).
H2SO4\text{H}_2\text{SO}_4 is a stronger acid than HNO3\text{HNO}_3 and forces HNO3\text{HNO}_3 to act as a base.
2
Identify the electrophile in Friedel-Crafts acylation
The catalyst AlCl3\text{AlCl}_3 abstracts Cl\text{Cl}^- from CH3COCl\text{CH}_3\text{COCl}, leaving the resonance-stabilized cations CH3C+=O\text{CH}_3\text{C}^+=\text{O}.
AlCl3\text{AlCl}_3 is an electron-deficient Lewis acid capable of coordinating chloride.
3
Identify the electrophile in bromination
FeBr3\text{FeBr}_3 coordinates with a bromine atom of Br2\text{Br}_2, polarising the bond to create an effective Br+\text{Br}^+ electrophile.
Benzene requires a Lewis acid catalyst to polarize halogen molecules sufficiently for reaction.
4
Identify the electrophile in sulfonation
Equilibrium in concentrated/fuming H2SO4\text{H}_2\text{SO}_4 produces neutral SO3\text{SO}_3, which has a highly electron-deficient sulfur atom.
The three electronegative oxygen atoms in SO3\text{SO}_3 withdraw electron density from the central sulfur atom.

Anahtar Kavram

Generation of Electrophiles in Benzene Electrophilic Substitution
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