Halogen Derivatives (Alkyl Halides & Aryl Halides)

Vocabulary flashcards covering classification, nomenclature, preparation, properties, reactions, and tests for alkyl and aryl halogen derivatives.

Halogen derivatives

Organic compounds in which one or more hydrogen atoms of a hydrocarbon are replaced by halogen atoms ($F$, $Cl$, $Br$, $I$), having the general formula $R-X$.

Alkyl halides (Haloalkanes)

Halogen derivatives with the general formula $R-X$ where $R$ is an alkyl group (e.g., $CH_3CH_2Cl$ / chloroethane).

Aryl halides (Haloarenes)

Halogen derivatives with the general formula $Ar-X$ where $Ar$ is an aryl group (e.g., $C_6H_5Cl$ / chlorobenzene).

Monohalides

Halogen derivatives classified by having one halogen atom, with the general formula $R-X$ (e.g., $CH_3Cl$).

Polyhalides

Halogen derivatives classified by having multiple halogen atoms, with the general formula $R-X_n$ (e.g., $CHCl_3$ / trichloromethane).

Methylene chloride (DCM)

The common name for the alkyl halide compound with the chemical formula $CH_2Cl_2$.

Carbon tetrachloride

The common name for the non-polar alkyl halide compound $CCl_4$, which is used as a solvent.

Free radical halogenation

The preparation of alkyl halides from alkanes: $R-H + X_2 \rightarrow R-X + HX$ (under $h\nu$ or $\text{heat}$, where $X = Cl, Br, I$).

Sandmeyer reaction

The method of preparing aryl halides from arene diazonium salts using a copper(I) halide: $Ar-N_2^+ + CuX \rightarrow Ar-X + N_2$ (where $X = Cl, Br$).

Iodoform

An exception to the generally colourless nature of halogen derivatives, known for having a yellow colour.

Boiling point trend of halogen derivatives

Increases in the order $F < Cl < Br < I$ due to increasing molecular mass.

Dehydrohalogenation

An elimination reaction where an alkyl halide reacts with alcoholic $KOH$ to form an alkene: $R-CH_2-CH_2-X + \text{alc. } KOH \rightarrow R-CH=CH_2 + KX + H_2O$.

Wurtz reaction

The reaction of alkyl halides with sodium metal to form higher alkanes: $2R-X + 2Na \rightarrow R-R + 2NaX$.

Finkelstein reaction

A halogen exchange reaction for alkyl halides: $R-Cl / R-Br + NaI \rightarrow R-I + NaCl / NaBr$ in acetone, driven by the precipitation of $NaCl$ or $NaBr$.

Beilstein test

A test for organic halides where heating the compound with a clean copper wire produces a green flame, indicating the presence of halogen.

Aqueous $AgNO_3$ test for $Cl^-$

Forms a white precipitate ($AgCl$) that is soluble in $NH_3$.

Aqueous $AgNO_3$ test for $Br^-$

Forms a cream precipitate ($AgBr$) that is partially soluble in $NH_3$.

Aqueous $AgNO_3$ test for $I^-$

Forms a yellow precipitate ($AgI$) that is insoluble in $NH_3$.

Reactivity order in $S_N1$

The order of reactivity for alkyl halides in $S_N1$ reactions: $3^\to > 2^\to > 1^\to$.

Reactivity order in $S_N2$

The order of reactivity for alkyl halides in $S_N2$ reactions: $1^\to > 2^\to > 3^\to$.

Reactivity towards aqueous $AgNO_3$

The relative order of halide reactivity towards aqueous silver nitrate: $I^- > Br^- > Cl^-$.

Freons

Alkyl halides utilized industrially and commercially as refrigerants.

$$CCl_3F$$

An alkyl halide compound utilized in fire extinguishers.

Halogen Derivatives

Organic compounds in which one or more hydrogen atoms of a hydrocarbon are replaced by halogen atoms ($\text{F}$, $\text{Cl}$, $\text{Br}$, or $\text{I}$).

Alkyl Halides (Haloalkanes)

Halogen derivatives with the general formula $R-X$ where a halogen is bonded to an alkyl group (e.g., chloroethane, $\text{CH}_3\text{CH}_2\text{Cl}$).

Aryl Halides (Haloarenes)

Halogen derivatives with the general formula $\text{Ar}-X$ where a halogen is attached directly to an aromatic ring (e.g., chlorobenzene, $\text{C}_6\text{H}_5\text{Cl}$).

Monohalides

Halogen derivatives that contain a single halogen atom per molecule, represented by the formula $R-X$ (e.g., $\text{CH}_3\text{Cl}$).

Polyhalides

Halogen derivatives containing multiple halogen atoms, represented by the general formula $R-X_n$ (e.g., trichloromethane, $\text{CHCl}_3$).

Free Radical Halogenation

A preparation method for alkyl halides from alkanes in the presence of light ($h\nu$) or heat ($\Delta$): $R-\text{H} + X_2 \xrightarrow{h\nu \text{ or } \Delta} R-X + \text{H}X$, where $X = \text{Cl}, \text{Br}, \text{I}$.

Alkene Hydrohalogenation

An electrophilic addition reaction where an alkene reacts with a hydrogen halide to produce an alkyl halide: $R\text{CH}=\text{CH}_2 + \text{H}X \rightarrow R\text{CH}X-\text{CH}_3$.

Sandmeyer Reaction

A preparation method for aryl halides from arene diazonium salts using cuprous halide: $\text{Ar}-\text{N}_2^+ + \text{Cu}X \rightarrow \text{Ar}-X + \text{N}_2$, where $X = \text{Cl}, \text{Br}$.

Iodoform

A yellow-coloured halogen derivative that serves as an exception to the generally colourless nature of halogen compounds.

Dehydrohalogenation

An elimination reaction where an alkyl halide reacts with alcoholic $\text{KOH}$ to produce an alkene, a halide salt, and water: $R-\text{CH}_2-\text{CH}_2-X + \text{alc. KOH} \rightarrow R-\text{CH}=\text{CH}_2 + \text{K}X + \text{H}_2\text{O}$.

Wurtz Reaction

A coupling reaction specific to alkyl halides in which two alkyl halide molecules react with sodium metal to form a higher alkane: $2R-X + 2\text{Na} \rightarrow R-R + 2\text{Na}X$.

Finkelstein Reaction

A halogen exchange reaction where an alkyl chloride or alkyl bromide reacts with sodium iodide in acetone to yield an alkyl iodide, driven by the precipitation of $\text{NaCl}$ or $\text{NaBr}$: $R-\text{Cl} / R-\text{Br} + \text{NaI} \xrightarrow{\text{acetone}} R-\text{I} + \text{NaCl} / \text{NaBr}$.

Aqueous $\text{AgNO}_3$ Test

A diagnostic test for halide ions ($X^-$) where $\text{Cl}^-$ produces a white precipitate ($\text{AgCl}$) soluble in $\text{NH}_3$, $\text{Br}^-$ produces a cream precipitate ($\text{AgBr}$) partially soluble in $\text{NH}_3$, and $\text{I}^-$ produces a yellow precipitate ($\text{AgI}$) insoluble in $\text{NH}_3$.

Beilstein Test

A qualitative flame test for organic halides where heating the compound on a clean copper wire produces a green flame, confirming the presence of halogen.

Lassaigne's Test

A chemical test used to identify nitrogen, sulfur, and halogens; yields a blue precipitate with $\text{AgNO}_3$ for $\text{Cl}^-$ and a yellow precipitate for $\text{Br}^- / \text{I}^-$ when soluble in $\text{HNO}_3$.

$\text{S}_\text{N}1$ Reactivity Order

The order of reactivity for alkyl halides in unimolecular nucleophilic substitution reactions: $3^\circ > 2^\circ > 1^\circ$.

$\text{S}_\text{N}2$ Reactivity Order

The order of reactivity for alkyl halides in bimolecular nucleophilic substitution reactions: $1^\circ > 2^\circ > 3^\circ$.

Trichlorofluoromethane ($\text{CCl}_3\text{F}$)

A polyhalogenated alkyl derivative used commercially in fire extinguishers.

Freons

A class of halogen derivatives commonly used industrially as refrigerants.

Halogen Electronic Effect

The electronic behavior of a halogen atom acting as electron-withdrawing via an inductive effect ($-I$ effect), while showing no positive mesomeric effect ($+M$ effect).