Organic Reactions Overview

Here’s an updated version of your notes with the sample reactions added under each relevant section:

Overview

This lecture covers the major reactions of alkanes, alkenes, and alkynes, focusing on combustion, halogenation, and addition reactions, with step-by-step examples and mechanisms.

Reactions of Alkanes

• Alkanes mainly undergo combustion and halogenation reactions.
• Combustion combines an alkane and oxygen to produce carbon dioxide (CO₂) and water (H₂O).
• Products of combustion are always CO₂ and H₂O, regardless of the size or complexity of the alkane.
• Halogenation replaces a hydrogen in an alkane with a halogen atom (e.g., F₂, Cl₂).
• In halogenation, one hydrogen is swapped for a halogen, producing a substituted alkane and hydrogen halide (e.g., HF, HCl).
• Multiple halogenations can occur if excess halogen is present, eventually replacing all hydrogens.

Sample Reactions for Alkanes

• Combustion:
  CH₄ + 2 O₂ → CO₂ + 2 H₂O
• Halogenation:
  CH₄ + Cl₂ → CH₃Cl + HCl

Reactions of Alkenes and Alkynes

• Alkenes have a carbon-carbon double bond; alkynes have a triple bond.
• Reactions occur at the multiple bonds and are typically addition reactions, combining two reactants into one product.
• Major addition reactions: hydrogenation, halogenation, hydrohalogenation, and hydration.

Hydrogenation

• Addition of H₂ to an alkene or alkyne converts double/triple bonds to single/double bonds, respectively.
• The product is a more saturated molecule (alkene → alkane, alkyne → alkene).

Sample Reaction:
CH₂=CH₂ + H₂ → CH₃–CH₃

Halogenation

• Addition of a halogen (e.g., Br₂, Cl₂) across a double or triple bond.
• Produces a dihalide (alkene → dihaloalkane, alkyne → dihaloalkene).

Sample Reaction:
CH₂=CH₂ + Br₂ → BrCH₂–CH₂Br

Hydrohalogenation

• Addition of a hydrogen halide (e.g., HCl, HBr) to an alkene or alkyne.
• Forms a haloalkane (or haloalkene), with possible structural isomers depending on which carbon receives the halogen.

Sample Reaction:
CH₂=CH₂ + HBr → CH₃–CH₂Br

Hydration

• Addition of water (H₂O) to an alkene or alkyne.
• Produces an alcohol (alkene → alcohol, alkyne → enol/ketone), with possible structural isomers.
• With excess water, further addition can occur on new double bonds.

Sample Reactions:

• Alkene hydration:
  CH₂=CH₂ + H₂O → CH₃–CH₂OH
• Alkyne hydration:
  CH≡CH + H₂O → CH₂=CHOH (enol, tautomerizes to acetaldehyde)

Key Terms & Definitions

• Alkane — hydrocarbon with only single C–C bonds.
• Alkene — hydrocarbon with at least one C=C double bond.
• Alkyne — hydrocarbon with at least one C≡C triple bond.
• Combustion — reaction with O₂ yielding CO₂ and H₂O.
• Halogenation — replacement of hydrogen(s) with halogen(s) in a hydrocarbon.
• Hydrogenation — addition of H₂ to multiple bonds, reducing their multiplicity.
• Hydrohalogenation — addition of HX (X = halogen) across double/triple bonds.
• Hydration — addition of H₂O to double/triple bonds to form alcohols.

Action Items / Next Steps

• Practice predicting products for combustion, halogenation, hydrogenation, hydrohalogenation, and hydration of given alkanes, alkenes, and alkynes.
• Review how to balance combustion reactions.
• Complete any assigned reaction product exercises from lecture.