topic 6D Flashcards
primary halogenoalkane
- one carbon attached to the carbon atom adjoining the halogen
secondary halogenoalkane
- two carbons attached to the carbon atom adjoining the halogen
tertiary halogenoalkane
- three carbons attached to the carbon atom adjoining the halogen
substitution
swapping a halogen atom for another atom or groups of atoms
nucleophile
electron pair donator e.g. OH-, NH3, CN-
what does the rate of substitution reactions depend on
- on the strength of the C-X bond
- the weaker the bond the easier it is to break and the faster the reaction
is water a good or poor nucleophile
- poor nucleophile but it can react slowly with halogenoalkanes in substitution reactions
nucleophilic substitution with aqueous hydroxide ions
- change in group
- reagent
- conditions
- mechanism
- role of reagent
- change in group: halogenoalkane to alcohol
- reagent: potassium or sodium hydroxide
- conditions: in aqueous solution; heat under reflux
- mechanism: nucleophilic substitution
- role of reagent: nucleophile, OH-
SN2 mechanism for halogenoalkanes
- primary halogenoalkane
- show the transition state
SN1 mechanism
- tertiary halogenoalkanes
- first the halogen breaks away from the halogenoalkane to for a carbocation intermediate
- the OH- nucleophile then attacks the positive carbon
nucelophilic substitution with ammonia
- change in group
- reagent
- conditions
- mechanism
- role of reagent
- change in group: halogenoalkane to amine
- reagent: NH3 dissolved in ethanol
- conditions: heat under pressure in sealed tube
- mechanism: nucleophilic substitution
- role of reagent: nucleophile
elimination with alcoholic hydroxide ions
- change in group
- reagent
- conditions
- mechanism
- role of reagent
- change in group: halogenoalkane to alkene
- reagent: potassium/sodium hydroxide
- conditions: in ethanol; heat
- mechanism: elimination
- role of reagent: base, OH-
hydrolysis reaction with aqueous silver nitrate
- aqueous silver nitrate is added to a halogenoalkane
- halide leaving group combines with a silver ion to form a silver halide precipitate
- the quicker the precipitate is formed the faster the substitution reaction hence the more reactive the haloalkane
rates of hydrolysis of iodo, bromo and chloroalkanes - fastest to slowest & colour of precipitate
- AgI - yellow precipitate
- AgBr - cream precipitate
- AgCl - white precipitate
rates of hydrolysis of primary, secondary & tertiary halogenoalkanes
- primary halogenoalkanes are the least reactive so will take the longest to produce a precipitate.
- then it’s secondary halogenoalkanes.
- tertiary halogenoalkanes are the most reactive so will produce a precipitate almost instantaneously