Haloalkanes and Haloarenes Lecture Notes

A collection of vocabulary terms and definitions regarding the chemistry of Haloalkanes and Haloarenes, including nomenclature, reactions, mechanisms, and specific polyhalogen compounds.

Alkyl halide (haloalkane)

A compound formed by replacing hydrogen atom(s) in an aliphatic hydrocarbon with halogen atom(s), where the halogen is attached to an $sp^3$ hybridised carbon.

Aryl halide (haloarene)

A compound formed by replacing hydrogen atom(s) in an aromatic hydrocarbon with halogen atom(s), where the halogen is attached to an $sp^2$ hybridised carbon.

Chloramphenicol

A chlorine-containing antibiotic produced by soil microorganisms, used for the treatment of typhoid fever.

Thyroxine

An iodine-containing hormone produced by the body; its deficiency causes the disease goiter.

Chloroquine

A synthetic halogen compound used for the treatment of malaria.

Halothane

A halogenated compound used as an anaesthetic during surgery.

Allylic halides

Compounds in which the halogen atom is bonded to an $sp^3$-hybridised carbon atom next to a carbon-carbon double bond ($C=C$).

Benzylic halides

Compounds in which the halogen atom is bonded to an $sp^3$-hybridised carbon atom next to an aromatic ring.

Vinylic halides

Compounds in which the halogen atom is bonded to an $sp^2$-hybridised carbon atom of a carbon-carbon double bond.

Geminal halides (gem-dihalides)

Dihalo-compounds where both halogen atoms are present on the same carbon atom.

Vicinal halides (vic-dihalides)

Dihalo-compounds where halogen atoms are present on adjacent carbon atoms.

Finkelstein reaction

The synthesis of alkyl iodides by the reaction of alkyl chlorides or bromides with $NaI$ in dry acetone.

Swarts reaction

The synthesis of alkyl fluorides by heating an alkyl chloride or bromide in the presence of metallic fluorides like $AgF$, $Hg_2F_2$, $CoF_2$, or $SbF_3$.

Sandmeyer’s reaction

A method to prepare aryl chlorides or bromides by treating a freshly prepared diazonium salt with cuprous chloride or cuprous bromide.

Ambident nucleophiles

Groups like cyanides and nitrites that possess two nucleophilic centres and can link through either atom (e.g., carbon or nitrogen).

$S_N2$ Mechanism

A bimolecular nucleophilic substitution reaction involving a single step transition state, following second order kinetics and resulting in inversion of configuration.

$S_N1$ Mechanism

A unimolecular nucleophilic substitution reaction occurring in two steps via a carbocation intermediate, following first order kinetics and resulting in racemisation.

Inversion of configuration

The stereochemical outcome of an $S_N2$ reaction where the spatial arrangement of the product is flipped relative to the reactant, like an umbrella turning inside out.

Optically active compounds

Compounds that rotate the plane of plane polarised light when it is passed through their solutions.

Dextrorotatory ($d$-form)

An optically active compound that rotates plane polarised light to the right (clockwise), indicated by a $(+)$ sign.

Laevorotatory ($l$-form)

An optically active compound that rotates plane polarised light to the left (anticlockwise), indicated by a $(-)$ sign.

Chiral

Objects or molecules that are non-superimposable on their mirror images; this property is known as chirality.

Achiral

Objects or molecules that are superimposable on their mirror images.

Enantiomers

Stereoisomers related to each other as non-superimposable mirror images that possess identical physical properties except for the direction of optical rotation.

Racemic mixture (racemic modification)

A mixture containing two enantiomers in equal proportions, resulting in zero optical rotation; represented by the prefix $(\\pm)$ or $dl$.

Racemisation

The process of converting an enantiomer into a racemic mixture.

Retention of configuration

The preservation of the integrity of the spatial arrangement of bonds to an asymmetric centre during a chemical reaction.

$\beta$-elimination

A reaction where a haloalkane is heated with alcoholic potassium hydroxide, leading to the removal of hydrogen from the $\beta$-carbon and halogen from the $\alpha$-carbon to form an alkene.

Zaitsev’s rule (Saytzeff rule)

In dehydrohalogenation reactions, the preferred product is the alkene that has the greater number of alkyl groups attached to the doubly bonded carbon atoms.

Organo-metallic compounds

Compounds containing carbon-metal bonds, such as Grignard reagents.

Grignard Reagents

Alkyl magnesium halides ($RMgX$) obtained by the reaction of haloalkanes with magnesium metal in dry ether.

Wurtz reaction

The reaction of alkyl halides with sodium in dry ether to give hydrocarbons containing double the number of carbon atoms present in the original halide.

Wurtz-Fittig reaction

The reaction of a mixture of an alkyl halide and an aryl halide with sodium in dry ether to produce an alkylarene.

Fittig reaction

The reaction of aryl halides with sodium in dry ether to produce compounds where two aryl groups are joined together.

Phosgene (Carbonyl chloride)

An extremely poisonous gas ($COCl_2$) formed by the slow oxidation of chloroform by air in the presence of light.

Freons

Chlorofluorocarbon compounds of methane and ethane that are extremely stable, unreactive, non-toxic, and used as aerosol propellants and refrigerants.

DDT ($p,p’$-Dichlorodiphenyltrichloroethane)

The first chlorinated organic insecticide, effective against malaria-carrying mosquitoes but banned in many places due to its toxicity and environmental stability.