6.5.2 Reactions of Halogenoalkanes

• What are halogenoalkanes derived from?

  Alkanes
• The carbon-halogen bond in halogenoalkanes is polar due to the higher electronegativity of the halogen
• Match the component with its description:

  Halogenoalkane ↔️ Organic compound with halogen atoms bonded to alkyl groups

  Halogen ↔️ Fluorine, chlorine, bromine, iodine

  Alkyl group ↔️ Carbon chain derived from alkanes

  Carbon-halogen bond ↔️ Polar covalent bond between carbon and halogen atoms
• What are the two primary types of reactions halogenoalkanes undergo?

  Nucleophilic substitution and elimination
• In nucleophilic substitution, the halogen atom is replaced by a nucleophile.
• Elimination reactions of halogenoalkanes lead to the formation of alkenes
• Under what conditions are elimination reactions favored?

  High temperature and concentrated base
• Steps in the SN1 reaction mechanism

  1️⃣ Carbocation formation

  2️⃣ Nucleophilic attack
• The SN2 reaction is a one-step process that results in inversion of stereochemistry.
• What two atoms are removed from adjacent carbon atoms during elimination reactions?

  Halogen and hydrogen
• Nucleophilic substitution reactions involve the displacement of a leaving group by a nucleophile
• The first step of the SN1 reaction is the formation of a carbocation.
• What is the stereochemical outcome of the SN1 reaction if the starting material is chiral?

  Racemization
• The SN2 reaction is favored in primary alkyl halides due to lower steric hindrance
• Match the feature with the correct nucleophilic substitution mechanism:

  Mechanism ↔️ SN1: Two-step ||| SN2: One-step

  Stereochemistry ↔️ SN1: Racemization ||| SN2: Inversion

  Carbocation formation ↔️ SN1: Yes ||| SN2: No
• What type of bond is formed during elimination reactions?

  Double bond
• The E1 reaction involves the formation of a carbocation in the first step.
• Steps in the E2 reaction mechanism

  1️⃣ Base removes a proton

  2️⃣ Leaving group departs

  3️⃣ Alkene formation
• The E2 reaction requires a trans-planar conformation between the proton and leaving group
• Under what conditions is the E2 reaction favored?

  Strong base and high temperature
• What is the mechanism for forming an alkene in the E1 reaction?

  Proton removal by a base
• The E1 reaction is favored in tertiary alkyl halides due to carbocation stability
• The E2 reaction is a one-step process that forms an alkene.
• What type of conformation is required in the E2 reaction between the proton and leaving group?

  Trans-planar
• Match the reaction feature with the correct reaction type:

  Mechanism ↔️ Two-step for E1

  Rate ↔️ Bimolecular for E2

  Conditions ↔️ Strong base for E2

  Carbocation Formation ↔️ Yes for E1
• What are halogenoalkanes derived from?

  Alkanes
• The carbon-halogen bond in halogenoalkanes is polar because halogens are more electronegative
• Halogenoalkanes undergo nucleophilic substitution and elimination reactions.
• What are the two types of nucleophilic substitution reactions that halogenoalkanes undergo?

  SN1 and SN2
• Order the steps involved in an elimination reaction of a halogenoalkane.

  1️⃣ Base removes a proton

  2️⃣ Halogen atom departs

  3️⃣ Alkene is formed
• In the elimination reaction of ethyl bromide with KOH, the major product formed is ethene
• What type of nucleophile is required for SN2 reactions of halogenoalkanes?

  Strong nucleophile
• What type of molecule is formed when halogenoalkanes undergo elimination reactions?

  Alkene
• Halogenoalkanes undergo two primary types of reactions: Nucleophilic Substitution and Elimination
• Steps involved in the elimination reaction of $CH_{3}CH_{2}Br$ with $KOH$


  1️⃣ Removal of the halogen atom and a hydrogen atom from adjacent carbon atoms

  2️⃣ Formation of a double bond between the carbon atoms

  3️⃣ Release of KBr and H2O
• What two primary types of reactions do halogenoalkanes undergo?

  Nucleophilic Substitution and Elimination
• In Nucleophilic Substitution, the halogen atom is replaced by a nucleophile
• Steps involved in the SN1 reaction of $(CH_{3})_{3}CBr$ with $H_{2}O$


  1️⃣ Formation of a carbocation by breaking the carbon-halogen bond

  2️⃣ Nucleophilic attack by water

  3️⃣ Formation of $(CH_{3})_{3}COH$ and $HBr$
• What is the rate law for the SN1 reaction?

  $rate =$$k[R - X]$
• The SN2 reaction prefers primary alkyl halides due to lower steric hindrance.