Reactions Of Halogenoalkanes 1 Chemsheets Answers Exclusive __top__ Jun 2026
| | Model Answer/Key Points | | :--- | :--- | | Define a nucleophile. | A nucleophile is a species with a lone pair of electrons, ready to donate to an electron-deficient carbon atom. Nucleophiles act as electron pair donors in reaction mechanisms. | | Why are halogenoalkanes attacked by nucleophiles? | The carbon-halogen bond is polar because the halogen is more electronegative, creating a δ⁺ carbon (electrophilic center) that attracts nucleophiles. | | In the reaction of a primary halogenoalkane with aqueous KOH, outline the mechanism. | Draw the SN2 mechanism showing a one-step process where the OH⁻ attacks from the opposite side of the leaving group (X⁻). Include partial bonds (---) in the transition state. | | What are the products when a secondary halogenoalkane is heated with ethanolic KOH? | The major product is the most substituted alkene (Saytzeff's rule). For example, 2-bromobutane produces but-2-ene (major) and but-1-ene (minor). | | Why are iodoalkanes the most reactive in nucleophilic substitution? | The C-I bond is the weakest despite being the least polar. Its low bond enthalpy makes it the easiest to break, leading to faster reactions. |
Halogenoalkanes are classified according to the carbon atom the halogen is bonded to:
Potassium hydroxide (KOH) or Sodium hydroxide (NaOH)
Cδ+−Xδ−C raised to the delta plus power minus X raised to the delta minus power The electron density is pulled toward the halogen atom ( ), leaving the carbon atom electron-deficient (
Substitution Nucleophilic Bimolecular (2 species in the rate-determining step). reactions of halogenoalkanes 1 chemsheets answers exclusive
CH₃CHBrCH₂CH₃ + OH⁻(ethanolic) →
The hydrolysis of halogenoalkanes involves their reaction with water, or more commonly, with aqueous sodium hydroxide (NaOH) to produce alcohols. This is a crucial nucleophilic substitution reaction. The hydroxide ion (OH⁻) acts as the attacking nucleophile, replacing the halogen atom. The general equation is:
The rate of reaction depends on the strength of the C-halogen bond. The C-F bond is the strongest and hardest to break, whereas the C-I bond is the weakest and breaks most easily. 2. Nucleophilic Substitution Reactions (Chemsheets Section)
The nucleophile uses its lone pair to form a new covalent bond with the electron-deficient carbon ( Cδ+C raised to the delta plus power | | Model Answer/Key Points | | :---
Halogenoalkanes undergo nucleophilic substitution with aqueous alkali, ethanolic potassium cyanide, and ammonia to form alcohols, nitriles, and primary amines, respectively. Additionally, elimination reactions occur with hot ethanolic KOH to produce alkenes, with reactivity increasing in the order C-Cl < C-Br < C-I. For the full resource, visit Chemsheets . REACTIONS OF HALOGENOALKANES 1 | Chemsheets
Ag(aq)++I(aq)−→AgI(s)(Rapid yellow precipitate)Ag sub open paren a q close paren end-sub raised to the positive power plus I sub open paren a q close paren end-sub raised to the negative power right arrow AgI sub open paren s close paren end-sub space (Rapid yellow precipitate)
) acts as an , making it highly susceptible to attack by electron-rich species known as nucleophiles .
Nucleophilic substitution can proceed via two primary pathways depending on the structure of the halogenoalkane (primary, secondary, or tertiary). SN2cap S sub cap N 2 Mechanism (Substitution Nucleophilic Bimolecular) | | Why are halogenoalkanes attacked by nucleophiles
Dissolved in ethanol, heated in a sealed copper tube (to prevent volatile ammonia gas from escaping) Nucleophile: Ammonia molecule ( :NH3:NH sub 3 General Equation:
Halogenoalkanes can also undergo elimination reactions to form . In this pathway, the hydroxide ion acts as a base (a proton acceptor) rather than a nucleophile. Reagents: Potassium hydroxide ( ) or Sodium hydroxide (
Produces pentanenitrile and potassium bromide.
While bond polarity determines how easily a nucleophile is attracted to the
Iodide > Bromide > Chloride (due to bond strength).
