Organic Reactions: Alkenes, Alkynes, and Benzene Derivatives

Vocabulary practice flashcards covering the addition reactions of alkenes and alkynes, electrophilic aromatic substitutions and functional group transformations of benzene, and aromatic nomenclature and substituent directing effects.

Electrophilic Addition to Alkenes (General Rule)

The general principle where the first step of each alkene addition reaction is the addition of an electrophile to the $sp^2$ carbon that is bonded to the greater number of hydrogens.

Addition of Hydrogen Halides to Alkenes

An electrophilic addition reaction where an alkene ($RCH=CH_2$) reacts with a hydrogen halide ($HX$, where $HX = HF, HCl, HBr, HI$) with $H^+$ acting as the electrophile, yielding an alkyl halide ($RCH(X)CH_3$).

Acid-Catalyzed Addition of Water to Alkenes

The addition of water ($H_2O$) across an alkene double bond catalyzed by $H_2SO_4$, where $H^+$ is the electrophile, producing a secondary alcohol ($RCH(OH)CH_3$).

Acid-Catalyzed Addition of Alcohols to Alkenes

The addition of an alcohol (such as $CH_3OH$) across an alkene double bond catalyzed by $H_2SO_4$, where $H^+$ is the electrophile, producing an ether ($RCH(OCH_3)CH_3$).

Addition of Halogens to Alkenes

The electrophilic addition of halogens ($Cl_2$ or $Br_2$) in solvent $CH_2Cl_2$, where $Cl^+$ or $Br^+$ serves as the electrophile, forming a vicinal dihalide ($RCH(Cl)CH_2Cl$ or $RCH(Br)CH_2Br$).

Halohydrin Formation

The addition of a halogen ($Br_2$) to an alkene in the presence of water ($H_2O$), yielding a halohydrin ($RCH(OH)CH_2Br$) where the halogen acts as the initial electrophile and water provides the nucleophile.

Oxymercuration–Reduction

A two-step reaction of an alkene using 1. $Hg(O_2CCH_3)_2, H_2O, THF$ followed by 2. $NaBH_4$, where $Hg$ acts as both the electrophile and the nucleophile, yielding an alcohol ($RCH(OH)CH_3$).

Alkoxymercuration–Reduction

A two-step reaction of an alkene using 1. $Hg(O_2CCF_3)_2, CH_3OH$ followed by 2. $NaBH_4$, where $Hg$ acts as both the electrophile and the nucleophile, yielding an ether ($RCH(OCH_3)CH_3$).

Addition of a Peroxyacid (Epoxidation)

The reaction of an alkene with a peroxyacid ($RCOOOH$) where oxygen ($O$) acts as both the electrophile and the nucleophile, forming an epoxide (oxirane) and a carboxylic acid ($RCOOH$).

Hydroboration–Oxidation of Alkenes

A two-step alkene hydration reaction using 1. $BH_3/THF$ and 2. $HO^-, H_2O_2, H_2O$, in which $B$ is the electrophile and $H^-$ is the nucleophile; $B$ is subsequently replaced by $OH$ to form an anti-Markovnikov primary alcohol ($RCH_2CH_2OH$).

Catalytic Hydrogenation of Alkenes

The addition of hydrogen ($H_2$) across an alkene double bond catalyzed by $Pd/C$ or $PtO_2$, reducing the alkene to an alkane ($RCH_2CH_3$).

Addition of Hydrogen Halides to Alkynes

Electrophilic addition where $H^+$ is the electrophile; reaction of an alkyne ($RC ≡ CH$) with one equivalent of $HX$ gives a haloalkene ($RC(X)=CH_2$), and reaction with excess $HX$ produces a geminal dihalide ($RC(X)_2CH_3$).

Addition of Halogens to Alkynes

The sequential addition of $Cl_2$ or $Br_2$ in $CH_2Cl_2$ across an alkyne, initially adding one halogen equivalent to form a dihaloalkene, followed by a second equivalent to produce a tetrahaloalkane.

Hydration of Internal Alkynes

The reaction of an internal alkyne ($RC ≡ CR'$) with either $H_2O, H_2SO_4$ or 1. $BH_3/THF$, 2. $HO^-, H_2O_2, H_2O$ to yield a mixture of ketones ($RC(=O)CH_2R'$ and $RCH_2C(=O)R'$).

Mercuric-Ion-Catalyzed Hydration of Terminal Alkynes

The addition of water to a terminal alkyne ($RC ≡ CH$) using $H_2O, H_2SO_4$ and $HgSO_4$, which proceeds via an enol intermediate ($RC(OH)=CH_2$) that tautomerizes to a methyl ketone ($RC(=O)CH_3$).

Hydroboration–Oxidation of Terminal Alkynes

The reaction of a terminal alkyne ($RC ≡ CH$) with 1. $BH_3/THF$ followed by 2. $HO^-, H_2O_2, H_2O$, proceeding through an enol intermediate ($RCH=CHOH$) to yield an aldehyde ($RCH_2CH=O$).

Lindlar Catalyst Hydrogenation

The selective hydrogenation of an internal alkyne ($R-C ≡ C-R'$) with $H_2$ in the presence of Lindlar catalyst to form a cis alkene.

Dissolving Metal Reduction of Alkynes

The reduction of an internal alkyne ($R-C ≡ C-R'$) using sodium or lithium ($Na$ or $Li$) in liquid ammonia ($NH_3(liq)$) at $-78\,^∘\text{C}$ to yield a trans alkene.

Alkynide Ion Alkylation

A two-step synthetic process wherein the proton of a terminal alkyne ($RC ≡ CH$) is removed by sodium amide ($NaNH_2$) to generate an acetylide anion ($RC ≡ C^-$), followed by alkylation with an alkyl halide ($R'CH_2Br$) to yield a substituted alkyne ($RC ≡ CCH_2R'$).

Electrophilic Chlorination of Benzene

The electrophilic aromatic substitution of benzene using $Cl_2$ with catalytic $FeCl_3$ (or other Lewis acids such as $AlCl_3$ or $ZrCl_4$) to yield chlorobenzene.

Electrophilic Bromination of Benzene

The electrophilic aromatic substitution of benzene using $Br_2$ catalyzed by $FeBr_3$ to produce bromobenzene; stoichiometric oxidants (e.g., $CuBr_2$, $HNO_3/H_2SO_4$) may also be used.

Friedel–Crafts Acylation

The reaction of benzene with an acyl chloride ($RCOCl$) in the presence of $AlCl_3$ to form an aryl ketone; no carbocation rearrangements occur, and the reaction fails if meta-directing substituents are present because they are too deactivating.

Friedel–Crafts Alkylation

The reaction of benzene with an alkyl chloride ($RCl$) and $AlCl_3$ to form an alkylbenzene; rearrangements can occur when primary alkyl halides are used.

Sulfonylation of Benzene

A reversible electrophilic aromatic substitution reaction between benzene and concentrated sulfuric acid ($H_2SO_4$) to yield benzenesulfonic acid ($Ph-SO_3H$).

Desulfonylation

The removal of the sulfonic acid group ($-SO_3H$) from an aromatic ring using $H_2SO_4$ and heat, allowing $-SO_3H$ to serve as a removable blocking group.

Nitration of Benzene

The electrophilic aromatic substitution of benzene using concentrated $HNO_3$ and $H_2SO_4$, where the nitronium ion ($NO_2^+$) generated in solution acts as the key electrophile to form nitrobenzene.

Nitro Group Reduction

The catalytic hydrogenation of a nitroarene to an aryl amine ($Ph-NH_2$) using $H_2$ over $Pd-C$, $Pt-C$, or $Ni$.

Wolff–Kishner Reduction

The reduction of an aryl ketone carbonyl to a methylene group using basic conditions: $KOH$, hydrazine ($NH_2NH_2$), and ethylene glycol ($HOCH_2CH_2OH$) with high heat.

Clemmensen Reduction

The reduction of an aryl ketone carbonyl to a methylene group under acidic conditions using zinc amalgam ($Zn(Hg)$) and strong acid ($H^+$).

Benzylic Bromination

A radical substitution reaction using $Br_2$ and peroxides that selectively functionalizes the benzylic position of an alkylbenzene to form a benzylic bromide.

Sidechain Oxidation of Alkylbenzenes

The oxidation of an alkylbenzene sidechain to a carboxylic acid ($-COOH$) using strong oxidants ($Na_2Cr_2O_7$ or $KMnO_4, H^+$ or $H_2CrO_4$); requires the benzylic carbon to have at least one $C-H$ bond.

Diazonium Salt Formation

The conversion of an aniline derivative into an arenediazonium salt using $NaNO_2$ and a strong acid ($HCl$), which in situ generates nitrous acid ($HNO_2$).

Sandmeyer Reaction

A set of copper(I)-catalyzed replacement reactions of arenediazonium salts using $CuCl$ for chlorination, $CuBr$ for bromination, or $CuCN$ for cyanation.

Fluorination of Diazonium Salts

The conversion of an arenediazonium salt to fluorobenzene using fluoroboric acid ($HBF_4$).

Phenol Synthesis from Diazonium Salts

The conversion of an arenediazonium salt into a phenol by treatment with $H_2SO_4, H_2O$ and heat, or alternatively using $Cu_2O, H_2O$.

Toluene (Toulene)

An aromatic hydrocarbon consisting of a benzene ring substituted with a single methyl group ($-CH_3$).

Phenol

An aromatic compound consisting of a benzene ring substituted with a hydroxyl group ($-OH$).

Aniline

An aromatic compound consisting of a benzene ring substituted with an amino group ($-NH_2$).

Anisole

An aromatic ether consisting of a benzene ring substituted with a methoxy group ($-OCH_3$).

Styrene

An aromatic hydrocarbon consisting of a benzene ring substituted with an ethenyl (vinyl) group ($-CH=CH_2$).

Benzaldehyde

An aromatic aldehyde consisting of a benzene ring substituted with a formyl group ($-CHO$).

Benzoic Acid

An aromatic carboxylic acid consisting of a benzene ring substituted with a carboxyl group ($-COOH$).

Xylene

A dimethyl-substituted benzene derivative having two methyl groups attached to the aromatic ring.

Cresol

A substituted benzene derivative bearing both a hydroxyl group ($-OH$) and a methyl group ($-CH_3$).

Ortho, Meta, and Para

Positional descriptors for disubstituted benzene rings: ortho designates 1,2-substitution, meta designates 1,3-substitution, and para designates 1,4-substitution.

Activating Groups (Aromatic Rings)

Substituents that provide lone pairs to the aromatic ring; they donate electron density, activate the ring toward electrophilic aromatic substitution, and direct electrophiles to the ortho and para positions.

Deactivating Groups (Aromatic Rings)

Substituents that do not provide lone pairs to the aromatic ring; they withdraw electron density, deactivate the ring toward electrophilic aromatic substitution, and direct electrophiles to the meta position.

Halogen Directing Effect Exception

A noted exception where halogen substituents are deactivating due to inductive electron withdrawal, but are ortho/para-directing due to resonance donation of their lone pairs.