Haloalkanes and Haloarenes

A comprehensive set of vocabulary flashcards covering classification, nomenclature, mechanisms, stereochemistry, reactions, and notable polyhalogen compounds from the Haloalkanes and Haloarenes unit.

Haloalkane (Alkyl Halide)

An organic compound in which one or more halogen atoms are bonded to an sp3-hybridised carbon of an alkyl group (R–X).

Haloarene (Aryl Halide)

An organic compound in which a halogen atom is directly bonded to an sp2-hybridised carbon of an aromatic ring.

Monohalo Compound

A molecule containing exactly one halogen atom.

Dihalo Compound

A molecule containing two halogen atoms; may be geminal or vicinal.

Polyhalo Compound

An organic molecule containing three or more halogen atoms (tri-, tetra-, etc.).

Primary (1°) Alkyl Halide

An alkyl halide in which the carbon bearing the halogen is attached to only one other carbon.

Secondary (2°) Alkyl Halide

An alkyl halide in which the carbon bearing the halogen is attached to two other carbons.

Tertiary (3°) Alkyl Halide

An alkyl halide in which the carbon bearing the halogen is attached to three other carbons.

Allylic Halide

A halide in which the halogen is bonded to an sp3 carbon adjacent to a C=C double bond.

Benzylic Halide

A halide in which the halogen is bonded to an sp3 carbon directly attached to an aromatic ring.

Vinylic Halide

A halogenated compound in which the halogen is bonded to an sp2 carbon of a C=C double bond.

Geminal Dihalide (gem-dihalide)

A molecule with two halogen atoms on the same carbon atom.

Vicinal Dihalide (vic-dihalide)

A molecule with two halogen atoms on adjacent carbon atoms.

Markovnikov’s Rule

In HX addition to an unsymmetrical alkene, the hydrogen attaches to the carbon with more hydrogens, giving the more substituted halide.

Finkelstein Reaction

Halogen exchange in which an alkyl chloride/bromide reacts with NaI in dry acetone to form an alkyl iodide.

Swarts Reaction

Preparation of alkyl fluorides by treating an alkyl chloride/bromide with metal fluorides such as AgF or SbF3.

Sandmeyer Reaction

Replacement of an aryldiazonium group by Cl, Br, or CN using cuprous salts (CuCl, CuBr, CuCN).

Grignard Reagent

An organomagnesium halide (RMgX) formed from an alkyl/aryl halide and Mg in dry ether; key organometallic reagent.

Wurtz Reaction

Coupling of alkyl halides with sodium metal in dry ether to give higher alkanes (doubling of carbon atoms).

Wurtz–Fittig Reaction

Coupling of an alkyl halide with an aryl halide in presence of sodium in dry ether to give alkylarenes.

Fittig Reaction

Coupling of two aryl halides with sodium in dry ether to yield biaryl compounds.

Nucleophilic Substitution (SN)

Reaction in which a nucleophile replaces a leaving group (halide) on an electrophilic carbon.

SN2 Mechanism

Bimolecular nucleophilic substitution involving a single transition state and inversion of configuration; rate ∝ [substrate][nucleophile].

SN1 Mechanism

Unimolecular nucleophilic substitution proceeding via a carbocation intermediate; rate ∝ [substrate] only; often yields racemic mixture.

β-Elimination (E2)

Removal of a β-hydrogen and a leaving group to form an alkene in one concerted step.

Zaitsev (Saytzeff) Rule

In β-elimination, the major alkene is the one with the greater number of alkyl groups on the double-bonded carbons.

Ambident Nucleophile

An anion with two different nucleophilic sites, e.g., CN⁻ (C- or N-attack) or NO₂⁻ (O- or N-attack).

Chirality

Property of a molecule that is non-superimposable on its mirror image; possesses a ‘handedness’.

Asymmetric (Chiral) Carbon

A tetrahedral carbon bonded to four different substituents; designated as a stereocentre.

Enantiomers

Non-superimposable mirror-image stereoisomers of a chiral molecule.

Racemisation

Conversion of an optically active compound into a 1:1 mixture of its enantiomers, resulting in optical inactivity.

Inversion of Configuration

The ‘umbrella flip’ stereochemical outcome in SN2 reactions where the configuration at the stereocentre is reversed.

Retention of Configuration

Stereochemical outcome where the spatial arrangement around the stereocentre remains unchanged after reaction.

Phenyl Cation

An unstable, non-resonance-stabilised carbocation derived from aryl halides; its instability hinders SN1 reactions of haloarenes.

Electrophilic Aromatic Substitution

Reaction in which an electrophile replaces a hydrogen on an aromatic ring, e.g., nitration, halogenation, sulphonation.

Ortho/Para-Directing

Describes substituents (like halogens) that direct incoming electrophiles to ortho and para positions on an aromatic ring.

β-Hydrogen

A hydrogen atom attached to the carbon adjacent (β-position) to the carbon bearing the leaving group.

Freon-12 (CCl₂F₂)

A chlorofluorocarbon refrigerant and aerosol propellant; stable but implicated in ozone depletion.

Dichloromethane (Methylene Chloride)

CH₂Cl₂; volatile solvent used in paint removers and degreasing; high exposure affects the CNS.

Chloroform (Trichloromethane)

CHCl₃; historical anesthetic, now mainly a feedstock for refrigerants; can form toxic phosgene on oxidation.

Iodoform (Triiodomethane)

CHI₃; yellow antiseptic compound with characteristic smell; formed in the iodoform test for methyl ketones.

Carbon Tetrachloride

CCl₄; non-flammable solvent and fire extinguisher once widely used; toxic and ozone-depleting.

DDT (p,p′-Dichlorodiphenyltrichloroethane)

A persistent chlorinated insecticide effective against mosquitoes; banned in many countries due to bioaccumulation.

Swarts/Finkelstein vs. Halogen Exchange

General term for reactions where one halogen atom in an alkyl halide is replaced by another via metal halide exchange.

Beta-Elimination vs Substitution

Competition in haloalkanes where strong, bulky bases favor elimination, whereas smaller nucleophiles favor substitution.