In a synthesis question, marks are given for the correct reagent and the correct conditions. The same reagent can give different products under different conditions, so the conditions must always be stated.Solvent: aqueous or ethanolic
• NaOH or KOH in water, warm: haloalkane → alcohol (substitution)
• KOH in ethanol, hot: haloalkane → alkene (elimination)Distil or reflux
• Primary alcohol + acidified K2Cr2O7, distil the product off as it forms → aldehyde
• Excess oxidising agent, heat under reflux → carboxylic acidExcess of one reactant
• Excess NH3 with a haloalkane → mainly primary amine
• Excess haloalkane → quaternary ammonium saltCatalysts
• Concentrated H2SO4: esterification and dehydration of alcohols
• H3PO4: hydration of alkenes with steam, at high temperature and pressure
• AlCl3: Friedel-Crafts acylation
• Ni: reduction with H2, for example of nitrilesOther conditions
• UV light: free-radical substitution of alkanes
• About 50 °C: nitration of benzene, to limit further nitration
• Dilute acid after KCN: to give the hydroxynitrile from an aldehyde or ketoneWorked example. Give the reagent and conditions to convert 2-bromopropane into propene. Answer: KOH dissolved in ethanol, heated. Writing only 'KOH' would not score, because warm aqueous KOH gives propan-2-ol instead.
• NaOH or KOH in water, warm: haloalkane → alcohol (substitution)
• KOH in ethanol, hot: haloalkane → alkene (elimination)Distil or reflux
• Primary alcohol + acidified K2Cr2O7, distil the product off as it forms → aldehyde
• Excess oxidising agent, heat under reflux → carboxylic acidExcess of one reactant
• Excess NH3 with a haloalkane → mainly primary amine
• Excess haloalkane → quaternary ammonium saltCatalysts
• Concentrated H2SO4: esterification and dehydration of alcohols
• H3PO4: hydration of alkenes with steam, at high temperature and pressure
• AlCl3: Friedel-Crafts acylation
• Ni: reduction with H2, for example of nitrilesOther conditions
• UV light: free-radical substitution of alkanes
• About 50 °C: nitration of benzene, to limit further nitration
• Dilute acid after KCN: to give the hydroxynitrile from an aldehyde or ketoneWorked example. Give the reagent and conditions to convert 2-bromopropane into propene. Answer: KOH dissolved in ethanol, heated. Writing only 'KOH' would not score, because warm aqueous KOH gives propan-2-ol instead.