This is a unimolecular reaction occurring in two steps.
By memorizing that sentence, you will never miss a question on “Reactions of Halogenoalkanes 1.”
Under different conditions, halogenoalkanes can undergo elimination rather than substitution, forming alkenes. Potassium Hydroxide ( KOHcap K cap O cap H Conditions: Ethanolic ( KOHcap K cap O cap H in ethanol), heat. What happens: The halogen and an atom on an adjacent carbon are removed, forming a double bond. Example: 2-chloropropane + hot, ethanolic KClcap K cap C l H2Ocap H sub 2 cap O Key Difference: Substitution vs. Elimination Aqueous OH−cap O cap H raised to the negative power = Substitution (Alcohol) Ethanolic OH−cap O cap H raised to the negative power = Elimination (Alkene) 4. Exclusive Summary of Chemsheets AS 1139 Answers
Nucleophilic substitution is the primary reaction type for halogenoalkanes. A nucleophile (a species with a lone pair that attacks the carbon) replaces the halogen atom. A. Reaction with Aqueous Sodium Hydroxide ( NaOH(aq)NaOH sub open paren a q close paren end-sub reactions of halogenoalkanes 1 chemsheets answers exclusive
Iodide > Bromide > Chloride (due to bond strength).
| Factor | Primary Halogenoalkane | Tertiary Halogenoalkane | | :--- | :--- | :--- | | | SN2 | SN1 | | Steric Hindrance | Low. Carbon is accessible to nucleophiles. | High. Bulky alkyl groups block attack by nucleophiles. | | Carbocation Stability | Primary carbocations are unstable. | Tertiary carbocations are stable due to +I inductive effect of alkyl groups. | | Reaction with NaOH(aq) | Fast substitution. | Slower substitution (due to steric hindrance), but can eliminate. |
) still has a lone pair on the nitrogen atom and can act as a nucleophile itself, leading to further substitution (secondary amines, tertiary amines, and quaternary ammonium salts). Using excess ammonia ensures the primary amine is the major product. This is a unimolecular reaction occurring in two steps
) acts as an , making it highly susceptible to attack by electron-rich species known as nucleophiles .
The relative rates of hydrolysis can be compared using a simple test. The halogenoalkane is warmed with a mixture of ethanol, water, and acidified silver nitrate (AgNO₃). The halide ion (X⁻) produced during hydrolysis reacts with Ag⁺ to form a precipitate of silver halide (AgX). The color of the precipitate identifies the halogen, and the time taken for it to appear indicates the reactivity: the faster the precipitate forms, the faster the reaction.
Heat in a sealed copper tube (to prevent the gas from escaping). Nucleophile: Product: Primary Amine. What happens: The halogen and an atom on
Understanding the Chemsheets AS 1030 answers isn't just about memorizing the products; it’s about recognizing the . Primary Halogenoalkanes favor Substitution . Tertiary Halogenoalkanes favor Elimination .
CH3CH2Br+CN−→CH3CH2CN+Br−cap C cap H sub 3 cap C cap H sub 2 cap B r plus cap C cap N raised to the negative power right arrow cap C cap H sub 3 cap C cap H sub 2 cap C cap N plus cap B r raised to the negative power C. Reaction with Ammonia ( NH3cap N cap H sub 3 Excess concentrated ammonia.
This article provides a comprehensive overview of the reactions covered in that worksheet, offering detailed explanations and key answers for student review. 1. Why Halogenoalkanes React: The Electrophilic Nature
As the halogen atom increases in size down Group 7, the C-X bond becomes weaker and longer. This is due to the poor orbital overlap between the carbon atom's small 2p orbital and the larger halogen orbitals.
R-X+OH−→R-OH+X−R-X plus OH raised to the negative power right arrow R-OH plus X raised to the negative power Mechanism 2: Cyanide Ions ( CN−CN raised to the negative power