Organic Chemistry Reaction Summary: Alkenes, Alkynes, and Haloalkanes/Radicals

Vocabulary review flashcards detailing the reaction types, reagents, regioselectivity, stereoselectivity, and product outcomes for alkene additions, alkyne reactions, and radical substitutions/additions.

Alkene Hydrohalogenation

An addition reaction in which an alkene reacts with $HX$ to form a haloalkane with Markovnikov ($M$) regioselectivity and no stereoselectivity ($N/A$). Carbocation rearrangements are possible, and a racemic mixture forms if at least one stereocenter is generated.

Alkene Hydration (Acid-Catalyzed)

An addition reaction in which an alkene reacts with $HOH$ in the presence of $H_2SO_4$ to form an alcohol with Markovnikov ($M$) regioselectivity and no stereoselectivity ($N/A$). Carbocation rearrangements are possible, and racemic mixtures form if at least one stereocenter is generated.

Alkene Halogenation

An addition reaction where an alkene reacts with a halogen ($X_2$) to produce a vicinal dihalide. The reaction has no regioselectivity ($N/A$), exhibits anti stereoselectivity, and forms a racemic mixture if stereocenters are produced.

Halohydrin Formation

An addition reaction in which an alkene is treated with $X_2$ and $H_2O$ (with loss of $-HX$) to produce a halohydrin. It displays Markovnikov ($M$) regioselectivity (the $-OH$ group adds to the more substituted carbon) and anti stereoselectivity, yielding a racemic mixture.

Alkene Hydroboration-Oxidation

A two-step addition sequence using 1) $R_2BH$ (or $BH_3$) followed by 2) $H_2O_2, NaOH$ to yield an alcohol from an alkene. It proceeds with non-Markovnikov ($NM$) regioselectivity and syn stereoselectivity in the first step, forming a racemic mixture.

Diol Formation (Alkene Dihydroxylation)

An oxidation reaction that converts an alkene into a vicinal diol using 1) $OsO_4$ and 2) $NaHSO_3, H_2O$. It exhibits no regioselectivity ($N/A$) and syn stereoselectivity in the first step, generating a racemic mixture.

Alkene Ozonolysis

An oxidative cleavage of an alkene using 1) $O_3$ and 2) $Me_2S$ ($(CH_3)_2S$) to yield two carbonyl fragments. It has no regioselectivity ($N/A$) and no stereoselectivity ($N/A$).

Alkene Hydrogenation

The catalytic reduction of an alkene to an alkane using $H_2/Pd$. It exhibits no regioselectivity ($N/A$) and syn stereoselectivity, forming a racemic mixture if stereogenic centers are generated.

Stereogenic Center Racemic Mixture Rule

A general principle in alkene additions stating that racemic mixtures will form if at least one (1 or more) stereocenter or stereogenic center is created in the reaction.

Carbocation Rearrangements in Alkene Additions

Structural carbocation rearrangements that are possible during the hydrohalogenation and acid-catalyzed hydration of alkenes due to open carbocation intermediates.

Alkyne Alkylation

A reaction where a terminal alkyne (R\text{-}C\tbond C\text{-}H) is deprotonated by $NaH$ (or $NaNH_2$) and alkylated using an alkyl halide ($R'\text{-}X$) to form an internal alkyne (R\text{-}C\tbond C\text{-}R'). It has no regioselectivity ($N/A$) and no stereoselectivity ($N/A$).

Alkyne Formation via Dehydrohalogenation ($\beta$-elimination)

The synthesis of alkynes from dihaloalkanes using strong base ($NaNH_2$). An internal alkyne requires $2\text{ equiv}$ of $NaNH_2$, whereas a terminal alkyne requires $3\text{ equiv}$ of $NaNH_2$ followed by an $H_3O^+$ workup. Overall stereoselectivity is $N/A$, but the elimination must occur anti to form a cis-alkene intermediate.

Halogenation of Alkynes

An electrophilic addition of halogen ($X_2$, where $X = Cl$ or $Br$) across an alkyne (R\text{-}C\tbond C\text{-}R') to yield a tetrahaloalkane ($R\text{-}CX_2\text{-}CX_2\text{-}R'$). It has no regioselectivity ($N/A$) and exhibits anti stereoselectivity, with both equivalents of $X_2$ added anti.

Addition of Hydrogen Halide to Alkynes

An electrophilic addition reaction in which an alkyne is treated with $HX$ to form a geminal dihalide ($R\text{-}CX_2\text{-}CH_2\text{-}R'$ or $R\text{-}CX_2\text{-}CH_3$). It shows Markovnikov ($M$) regioselectivity and no stereoselectivity ($N/A$).

Hydroboration-Oxidation of Alkynes

A reaction using 1) $R_2BH$ and 2) $H_2O_2, NaOH_{(aq)}$. An internal alkyne produces a ketone mixture, while a terminal alkyne yields an aldehyde (via an enol intermediate). It exhibits non-Markovnikov ($NM$) regioselectivity and syn stereoselectivity, as $H$ and $BR_2$ add to the same face.

Acid-Catalyzed Hydration of Alkynes

A hydration reaction using $H_2SO_4$ and $H_2O$. An internal alkyne yields a ketone mixture, whereas a terminal alkyne yields a single ketone (via an enol intermediate). The reaction proceeds with Markovnikov ($M$) regioselectivity and no stereoselectivity ($N/A$).

Hydrogenation of Alkynes to Alkanes

The complete catalytic reduction of an alkyne to an alkane using $H_2/Pd$. It displays no regioselectivity ($N/A$) and syn stereoselectivity, with both molecules of $H_2$ added to the same face.

Hydrogenation of Alkynes to CIS-Alkenes

The partial catalytic reduction of an internal alkyne to a cis-alkene using $H_2$ with Lindlar catalyst. It shows no regioselectivity ($N/A$) and syn stereoselectivity.

Hydrogenation of Alkynes to TRANS-Alkenes

The dissolving metal reduction of an internal alkyne to a trans-alkene using sodium in liquid ammonia ($Na / NH_3(l)$). It shows no regioselectivity ($N/A$) and anti stereoselectivity.

Free-Radical Substitution with $Br_2$ (with light/heat)

A radical halogenation converting an alkane to an alkyl halide using $Br_2$ under heat ($\Delta$) or light ($h\nu$). It proceeds with Markovnikov ($M$) regioselectivity to produce the major product and shows no stereoselectivity ($N/A$).

Allylic Substitution with NBS

A radical bromination reaction transforming an alkene into an allylic haloalkene using $N\text{-bromosuccinimide}$ ($NBS$) and light ($h\nu$). It proceeds with Zaitsev regioselectivity and exhibits no stereoselectivity ($N/A$).

Addition of HBr to Alkenes with Peroxide

A radical addition reaction converting an alkene into a non-Markovnikov alkyl halide using $HBr$ in the presence of peroxides ($ROOR$). It proceeds with non-Markovnikov ($NM$) regioselectivity and exhibits no stereoselectivity ($N/A$).