Delocalized Electrons, Aromaticity, and Electrophilic Aromatic Substitution

Flashcards covering key concepts and definitions related to delocalized electrons, aromaticity, and electrophilic aromatic substitution in organic chemistry.

Delocalized Electrons

Electrons that are shared by three or more atoms, playing a crucial role in the stability and reactivity of molecules.

Localized Electrons

Electrons that are restricted to a particular region, belonging to a single atom or shared by two atoms.

Aromatic Compound

A compound that is cyclic, planar, has an uninterrupted cloud of p electrons, and contains an odd number of pairs of p electrons.

pKa Value

A measure of the acidity of a compound; the lower the pKa, the stronger the acid.

Electrophilic Addition Reaction

A reaction where an electrophile reacts with a nucleophile, typically involving alkenes.

Electrophilic Aromatic Substitution

A reaction where an electrophile replaces a hydrogen atom on an aromatic ring, preserving aromaticity.

Kekulé Structure

A representation of benzene with alternating double bonds, which does not accurately describe its delocalized nature.

Resonance Contributors

Structures that can be drawn for a compound by moving electrons, representing different possible forms of the molecule.

Delocalization Energy

The energy associated with the added stability of a compound due to the delocalization of electrons.

Resonance Hybrid

The actual structure of a molecule that is a blend of all possible resonance contributors, accounting for electron delocalization.

Friedel–Crafts Acylation

An electrophilic aromatic substitution that introduces an acyl group into a benzene ring, requiring an acyl chloride or acid anhydride.

Acylium Ion

The electrophilic species generated during Friedel–Crafts acylation that reacts with the benzene ring.

Substitution Reaction

A reaction where one atom or group is replaced with another atom or group, as seen in electrophilic aromatic substitution.

Hückel's Rule

The principle stating that a planar, cyclic compound must have an odd number of pairs of p electrons to be classified as aromatic.

Benzylic Cation

A carbocation where the positive charge is on a benzylic carbon adjacent to an aromatic ring, stabilizing it through delocalization.

Allylic Cation

A carbocation with a positive charge on an allylic carbon adjacent to a double bond.

Benzene

An aromatic hydrocarbon with the formula C6H6, known for its stability due to delocalized electrons.

Carbocation Stability

The stability of carbocations increases with the number of alkyl groups attached, leading to tertiary > secondary > primary stability.

Coupling Reaction

A reaction that forms a carbon-carbon bond by coupling two reactants, often involving a transition metal catalyst.