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 bromoethane reacts with aqueous to yield ethanol and a bromide ion. Reaction B: Nitrile Formation (Cyanide Substitution) Reagents: Potassium cyanide ( ) dissolved in ethanol. Conditions: Heating under reflux. Nucleophile: Cyanide ion (
CH₃CHBrCH₂CH₃ + OH⁻(ethanolic) →
R-X+CN−→R-C≡N+X−R-X plus CN raised to the negative power right arrow R-C triple bar N plus X raised to the negative power reactions of halogenoalkanes 1 chemsheets answers exclusive
A common exam challenge is determining whether a reaction will proceed via substitution or elimination. Use this summary table to guide your answers: Nucleophilic Substitution Elimination Aqueous (dissolved in water) Ethanolic (dissolved in ethanol) Temperature Warm / Moderate Hot / High Temperature Role of OH−OH raised to the negative power Nucleophile (electron pair donor) Base (proton acceptor) Halogenoalkane Structure Favored by Primary ( 1∘1 raised to the composed with power Favored by Tertiary ( 3∘3 raised to the composed with power
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 ( Reagents: Potassium hydroxide ( ) or Sodium hydroxide
dissolved in hot, pure ethanol) at high temperatures. Ethanol alters the behavior of the hydroxide ion, causing it to act strictly as a strong (proton acceptor) rather than a nucleophile. Mechanism and Isomerism
Most of the "Reactions of Halogenoalkanes 1" focuses on substitution, where the halogen atom is replaced by a nucleophile. A. Reaction with Aqueous Potassium Hydroxide ( OH−cap O cap H raised to the negative power Conditions: Warm/Reflux Nucleophile: Hydroxide ion ( Product: Alcohol Equation: reactions of halogenoalkanes 1 chemsheets answers exclusive
| Reaction | Reagent & conditions | Product | Mechanism | |----------|----------------------|---------|------------| | 1-bromopropane + NaOH(aq) | NaOH(aq), warm | propan-1-ol | SN2 | | 2-bromo-2-methylpropane + NaOH(aq) | NaOH(aq), room temp | 2-methylpropan-2-ol | SN1 | | 1-chlorobutane + KCN | KCN in ethanol/water, reflux | pentanenitrile | SN2 | | 2-bromobutane + NH₃(excess) | conc NH₃ in ethanol, sealed tube, heat | butan-2-amine | SN2 (with excess NH₃ to avoid further substitution) | | 2-bromopropane + NaOH/ethanol | NaOH in ethanol, heat | propene | E2 | | 1-bromo-2-methylpropane + H₂O | H₂O, slow hydrolysis | 2-methylpropan-1-ol | SN2 (very slow) |
This reaction is crucial in organic synthesis because it increases the carbon chain length by one carbon atom. General Equation: