Organic Chemistry Exam #3 review

Comprehensive vocabulary and conceptual flashcards covering nucleophilic substitution, elimination, and addition reactions to alkenes

Elimination Reaction

A reaction type where a substrate, such as an alkyl halide, reacts to form an alkene by losing atoms (like a hydrogen and a halogen).

SN2 Rate Equation

The reaction rate for a bimolecular substitution, represented as $Rate = k[substrate][nucleophile]$.

SN1 Stereochemistry

A reaction that results in about a 50:50 mixture of retention and inversion of configuration at the electrophilic center.

Nucleophile

An electron-rich species (such as $OH^-$, $CH_3OH$, or $NH_3$) that donates an electron pair to form a new bond.

Electrophile

The species in a reaction (such as the carbon in 2-chlorobutane) that is attacked by a nucleophile because it is electron-deficient.

Leaving Group

The atom or group (such as $Cl^-$) that detaches from the organic molecule during a substitution or elimination reaction.

Oxymercuration of an Alkene

A reaction involving $Hg(OAc)_2$ and water that follows Markovnikov orientation with anti-addition.

Catalytic Reduction

A process using hydrogen gas ($H_2$) and a palladium ($Pd$) catalyst to saturate double bonds; for 1,3-dibromocyclohexa-1,4-diene, 2 moles of $H_2$ are consumed.

Ozonolysis Reagents

A sequence typically involving 1. $O_3$ and 2. $Me_2S$ (or $Zn/H_2O$) used to cleave double bonds into carbonyl groups.

SN2 Reactivity Trend

The ranking of halides from most to least reactive based on steric hindrance, generally where primary halides are more reactive than secondary, which are more reactive than tertiary.

MCPBA

A reagent ($m$-chloroperoxybenzoic acid) used as a step in organic synthesis, often to form epoxides from alkenes.

Hydroboration-Oxidation Reagents

A two-step sequence involving 1. $BH_3 ext{·} THF$ and 2. $H_2O_2$, $NaOH$ used to achieve anti-Markovnikov hydration of an alkene.

Aprotic Solvent in SN2

A solvent like acetonitrile ($CH_3CN$) that is used with reagents like $NaN_3$ to provide high yields of substitution products.

Polar aprotic solvents

Solvents that favor $S_N2$ reactions because they cannot stabilize anions, causing nucleophiles to have higher energy.

E2 elimination

A concerted elimination reaction typically represented on an energy diagram by a single transition state without an intermediate.

Tertiary alkyl halide

A classification of alkyl halide where the halogen-bearing carbon is attached to three other carbons; an example is $\text{2-Bromo-2-methylpropane}$.

Concerted elimination mechanism

A mechanism, such as $E2$, where the removal of a proton and the loss of a leaving group occur simultaneously in one step.

Secondary halide

An alkyl halide where the carbon attached to the halogen is bonded to two other carbon atoms.

Rate of an $S_N2$ reaction

Dependent on the concentration of both the substrate and the nucleophile; doubling the substrate while halving the nucleophile results in no net effect on the rate.

Slowest $S_N2$ reaction

Occurs with the most sterically hindered alkyl halide, typically a tertiary halide or one with significant branching near the leaving group.

Solvolysis with $H_2O$

A reaction condition that typically results in a mixture of $S_N1$ or $E1$ products.

$S_N1$ Rate Equation

$\text{Rate} = k[ ext{alkyl halide}]$, where the rate depends only on the concentration of the substrate and is independent of the nucleophile.

$S_N2$ Transition State

A pentacoordinate state where the nucleophile and leaving group are partially bonded to the central carbon, often denoted with partial charges ($\delta^-$).

Bromination of (E)-3-hexene

The addition of $Br_2$ to an alkene which, through anti-addition, produces a meso dibromide.

Anti-Markovnikov Hydrohalogenation

The reaction of an alkene with $HBr$ in the presence of peroxides ($ext{ROOR}$) to place the bromine on the less substituted carbon.

Pi ($ext{\pi}$) bond

The component of an alkene that acts as a nucleophile during an addition reaction.

Oxymercuration-demercuration

A two-step sequence ($1. Hg(OAc)_2, H_2O; 2. NaBH_4, NaOH$) that yields a Markovnikov alcohol without carbocation rearrangement.

Bromonium ion

The reaction intermediate formed when an alkene like $4 ext{-methylcyclohexene}$ reacts with $Br_2$ in $\text{CCl}_4$.

Ozonolysis

The treatment of an alkene with ozone ($O_3$) followed by zinc and water ($ext{Zn/H}_2 ext{O}$) to cleave the double bond into carbonyl compounds.

Dehydration of alcohols

The conversion of an alcohol to an alkene using acid like concentrated $H_2SO_4$, proceeding through a carbocation intermediate.

Dihydroxylation (Syn)

The reaction using catalytic $OsO_4$ and $\text{NMO}$ to add two hydroxyl ($ext{OH}$) groups to the same side of an alkene.

Hydroboration-oxidation

A sequence ($1. BH_3 imes THF; 2. H_2O_2, NaOH$) that produces an anti-Markovnikov alcohol via syn-addition.

MCPBA followed by acid hydrolysis

A sequence ($1. MCPBA; 2. H^+, H_2O$) that results in the anti-dihydroxylation of an alkene.