Summary of Key Organic Chemistry Reactions: Substitution, Elimination, Addition, and Radical Mechanisms

Substitution Reactions

Alcohol from Primary Halide

Primary alkyl halides can be converted to alcohols via nucleophilic substitution, typically using aqueous hydroxide.

• Key Point: The reaction proceeds via an SN2 mechanism for primary halides.

• Equation: $\ce{R-CH2-X + OH^- -> R-CH2-OH + X^-}$

• Example: 1-bromopropane reacts with NaOH to yield 1-propanol.

Alcohol from Tertiary Halide (Solvolysis)

Tertiary alkyl halides react with water or alcohols to form alcohols via an SN1 mechanism.

• Key Point: Carbocation intermediates are formed, allowing rearrangements.

• Equation: $\ce{(CH3)3C-Br + H2O -> (CH3)3C-OH + HBr}$

Ether Formation

Ethers can be synthesized from primary or secondary halides using alkoxide ions (Williamson ether synthesis).

• Key Point: SN2 mechanism; works best with primary halides to avoid elimination.

• Equation: $\ce{R-CH2-X + R'-O^- -> R-CH2-O-R' + X^-}$

Halide Exchange (Finkelstein Reaction)

Halide exchange allows conversion between different alkyl halides, commonly using NaI in acetone.

• Key Point: Useful for preparing alkyl iodides from alkyl chlorides or bromides.

• Equation: $\ce{R-CH2-Cl + NaI -> R-CH2-I + NaCl}$

Thiol Formation

Thiols are synthesized from alkyl halides using sodium hydrosulfide (NaSH).

• Equation: $\ce{R-CH2-X + NaSH -> R-CH2-SH + NaX}$

Ether from Alcohol (Acid-Catalyzed)

Alcohols can be converted to ethers under acidic conditions, often with rearrangement for secondary/tertiary alcohols.

• Equation: $\ce{2 R-OH \xrightarrow{H^+} R-O-R + H2O}$

Nitrile Formation from Primary Halides

Primary alkyl halides react with cyanide ion to form nitriles (SN2 mechanism).

• Equation: $\ce{R-CH2-X + NaCN -> R-CH2-CN + NaX}$

Alkylation of Terminal Alkynes

Terminal alkynes can be alkylated with primary alkyl halides after deprotonation with a strong base (e.g., NaNH2).

• Equation: $\ce{RC#CH + NaNH2 -> RC#C^- Na^+}$ $\ce{RC#C^- + R'-X -> RC#C-R'}$

Formation of Sulfonate Esters

Conversion of Alcohols to Tosylates

Alcohols react with tosyl chloride (TsCl) to form tosylates, which are better leaving groups for substitution and elimination reactions.

• Equation: $\ce{R-OH + TsCl -> R-OTs + HCl}$

Elimination Reactions

Dehydrohalogenation (E2/E1 Mechanisms)

Alkyl halides can be converted to alkenes by elimination of HX using a strong base.

• Equation: $\ce{R-CH2-CH2-X + B^- -> R-CH=CH2 + HB + X^-}$

• Key Point: Zaitsev's rule often applies: the more substituted alkene is favored.

Dehydration of Alcohols

Alcohols can be dehydrated to alkenes using acid catalysis (E1 or E2, depending on substrate).

• Equation: $\ce{R-CH2-CH2-OH \xrightarrow{H_2SO_4} R-CH=CH2 + H2O}$

Synthesis of Alkynes from Dihalides

Vicinal dihalides can be converted to alkynes by double elimination using strong base (e.g., NaNH2).

• Equation: $\ce{R-CHX-CHX-R' + 2 NaNH2 -> RC#CR' + 2 NaX + 2 NH3}$

Addition Reactions

Hydrohalogenation of Alkenes (Markovnikov and Anti-Markovnikov)

Alkenes react with HX (HCl, HBr, HI) to form alkyl halides. Markovnikov's rule applies unless peroxides are present (anti-Markovnikov for HBr).

• Equation: $\ce{RCH=CH2 + HBr -> RCHBr-CH3}$

Hydration of Alkenes

Alkenes react with water in the presence of acid to form alcohols (Markovnikov addition).

• Equation: $\ce{RCH=CH2 + H2O \xrightarrow{H^+} RCH(OH)-CH3}$

Oxymercuration-Demercuration

Addition of water to alkenes using mercuric acetate and sodium borohydride yields Markovnikov alcohols without rearrangement.

• Equation: $\ce{RCH=CH2 + Hg(OAc)2, H2O; NaBH4 -> RCH(OH)-CH3}$

Hydroboration-Oxidation

Alkenes react with borane followed by hydrogen peroxide to yield anti-Markovnikov alcohols (syn addition).

• Equation: $\ce{RCH=CH2 + BH3; H2O2, OH^- -> RCH2CH2OH}$

Hydrogenation of Alkenes and Alkynes

Addition of hydrogen (H2) to alkenes or alkynes using metal catalysts (e.g., Pd/C, Pt, Ni) yields alkanes (syn addition).

• Equation: $\ce{RCH=CH2 + H2 \xrightarrow{Pd/C} RCH2CH3}$

Addition of Halogens (Cl2, Br2)

Alkenes react with halogens to form vicinal dihalides (anti addition).

• Equation: $\ce{RCH=CH2 + Br2 -> RCHBr-CH2Br}$

Halohydrin Formation

Alkenes react with halogen and water to form halohydrins (anti addition).

• Equation: $\ce{RCH=CH2 + Br2, H2O -> RCH(OH)-CH2Br}$

Dihydroxylation of Alkenes

Syn addition of two hydroxyl groups to an alkene using cold, dilute KMnO4 or OsO4.

• Equation: $\ce{RCH=CH2 + OsO4 -> RCH(OH)-CH2OH}$

Epoxidation and Epoxide Opening

Alkenes react with peracids (e.g., mCPBA) to form epoxides, which can be opened to trans diols with acid or base.

• Equation: $\ce{RCH=CH2 + RCO3H -> RCH(O)-CH2O}$ (epoxide)

Cleavage of Alkenes (Oxidative Cleavage)

Alkenes can be cleaved to carbonyl compounds using ozone (ozonolysis) or hot KMnO4.

• Equation (ozonolysis): $\ce{RCH=CHR' + O3 -> RCHO + R'CHO}$

Radical Reactions

Halogenation of Alkanes

Alkanes react with Cl2 or Br2 under UV light to form alkyl halides via a radical chain mechanism.

• Key Point: Bromination is more selective than chlorination.

• Equation: $\ce{RH + Br2 \xrightarrow{hv} RBr + HBr}$

Allylic Bromination

Allylic hydrogens can be selectively brominated using N-bromosuccinimide (NBS) under radical conditions.

• Equation: $\ce{RCH=CH-CH3 + NBS \xrightarrow{hv} RCH=CH-CH2Br}$

Autoxidation of Organics

Organic compounds can undergo autoxidation to form peroxides, which are often unstable and potentially explosive.

• Key Point: Peroxides form via radical chain mechanisms, especially in ethers.

Summary Table: Major Reaction Types and Examples

Reaction Type	General Equation	Example
Substitution (SN2)	$\ce{R-X + Nu^- -> R-Nu + X^-}$	1-bromopropane + NaOH → 1-propanol
Elimination (E2)	$\ce{R-CH2-CH2-X + B^- -> R-CH=CH2 + HB + X^-}$	2-bromobutane + KOH → 2-butene
Addition (Markovnikov)	$\ce{RCH=CH2 + HBr -> RCHBr-CH3}$	Propene + HBr → 2-bromopropane
Radical Halogenation	$\ce{RH + Br2 \xrightarrow{hv} RBr + HBr}$	Methane + Br2 → bromomethane

Additional info: This summary covers core reactions from the first semester of organic chemistry, focusing on mechanisms, reagents, and typical products. For each reaction, understanding the underlying mechanism is crucial for predicting outcomes and solving synthesis problems.