Haloalkanes and Haloarenes

Vocabulary flashcards covering the key definitions, classifications, named reactions, and stereochemical principles of haloalkanes and haloarenes.

Haloalkanes

Compounds containing halogen atoms attached to an alkyl group, represented by the general formula $R-X$ (where $X = F, Cl, Br, I$).

Haloarenes

Compounds containing halogen atoms attached to an aryl group, represented by the general formula $Ar-X$ (where $X = F, Cl, Br, I$).

Allylic halides

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

Benzylic halides

Compounds in which the halogen atom is bonded to an $sp^3$-hybridised carbon atom directly attached to a benzene ring.

Vinylic halides

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

Aryl halides

Compounds in which the halogen atom is bonded directly to an $sp^2$-hybridised carbon atom of an aromatic ring.

Lucas Reagent

A reagent mixture of concentrated $HCl$ and anhydrous $ZnCl_2$ used to convert alcohols to alkyl chlorides.

Markownikoff's rule

The rule stating that when an unsymmetrical reagent is added to an unsymmetrical alkene, the negative part of the adding molecule attaches to the carbon atom with the lesser number of hydrogen atoms.

Test for unsaturation

A chemical test where the discharge of the reddish brown colour of bromine ($Br_2$) in $CCl_4$ indicates the presence of a carbon-carbon double or triple bond.

Finkelstein reaction

A halogen exchange reaction where alkyl chlorides or bromides are treated with $NaI$ in dry acetone to produce alkyl iodides.

Swarts reaction

A reaction where an alkyl chloride or bromide is heated with a metallic fluoride (such as $AgF$, $Hg_2F_2$, $CoF_2$, or $SbF_3$) to yield an alkyl fluoride.

Diazotisation

The reaction in which an aromatic primary amine is treated with a mineral acid like $HCl$ and sodium nitrite ($NaNO_2$) at cold temperatures ($0\text{--}5^\bot\text{C}$) to produce an aromatic diazonium salt.

Sandmeyer's reaction

The chemical conversion of a diazonium salt to a halobenzene by treatment with $HX$ in the presence of cuprous halide ($Cu_2X_2$).

Gattermann's reaction

The reaction of a benzene diazonium salt with hydrogen halide in the presence of copper powder (instead of cuprous halide) to yield a halobenzene.

Dehydrohalogenation ($\beta$-elimination)

An elimination reaction where an alkyl halide having a $\beta$-hydrogen atom is treated with alcoholic $KOH$, resulting in the loss of a hydrogen halide molecule to yield an alkene.

Saytzeff rule

The rule stating that during dehydrohalogenation, if more than one alkene can be formed, the preferred product is the alkene with the greater number of alkyl groups attached to the doubly bonded carbons.

Grignard reagent

An organomagnesium halide with the general formula $RMgX$, synthesized by reacting an alkyl halide with magnesium metal in an ether medium.

Wurtz reaction

The reaction of alkyl halides with sodium metal in dry ether to yield symmetrical alkanes containing double the number of carbon atoms.

Nucleophilic Substitution Reaction

A class of reactions in which a weaker nucleophile (leaving group) is replaced by a stronger incoming nucleophile.

Williamson's ether synthesis

The preparation of ethers ($R-O-R$) through the reaction of a haloalkane with a sodium alkoxide ($R-ONa$).

Substitution Nucleophilic unimolecular ($S_N1$)

A two-step nucleophilic substitution mechanism that proceeds through a carbocation intermediate, with alkyl halide reactivity order of $3^\bot\circ > 2^\bot\circ > 1^\bot\circ$.

Substitution Nucleophilic bimolecular ($S_N2$)

A single-step concerted nucleophilic substitution mechanism with no intermediate, resulting in inversion of configuration and an alkyl halide reactivity order of $1^\bot\circ > 2^\bot\circ > 3^\bot\circ$.

Inversion of configuration

The flipping of the spatial arrangement of bonds at a chiral carbon centre during a backside nucleophilic attack in an $S_N2$ reaction.

Dextrorotatory ($d$-form or $+$ form)

A property of an optically active compound that rotates plane-polarised light towards the right (in a clockwise direction).

Laevorotatory ($l$-form or $-$ form)

A property of an optically active compound that rotates plane-polarised light towards the left (in an anticlockwise direction).

Optical isomers

The dextrorotatory ($d$) and laevorotatory ($l$) forms of a compound that rotate plane-polarised light in equal magnitudes but opposite directions.

Chiral molecule

A molecule that contains a carbon atom bonded to four different groups, rendering it non-superimposable on its mirror image.

Achiral molecule

A molecule that is superimposable on its mirror image.

Enantiomers

Stereoisomers that are related to each other as non-superimposable mirror images.

Racemic mixture

An equimolar mixture containing the $d$ and $l$ forms of a compound that exhibits zero optical rotation due to mutual cancellation of optical activity.