topic 6D Flashcards

1
Q

primary halogenoalkane

A
  • one carbon attached to the carbon atom adjoining the halogen
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2
Q

secondary halogenoalkane

A
  • two carbons attached to the carbon atom adjoining the halogen
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3
Q

tertiary halogenoalkane

A
  • three carbons attached to the carbon atom adjoining the halogen
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4
Q

substitution

A

swapping a halogen atom for another atom or groups of atoms

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5
Q

nucleophile

A

electron pair donator e.g. OH-, NH3, CN-

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6
Q

what does the rate of substitution reactions depend on

A
  • on the strength of the C-X bond
  • the weaker the bond the easier it is to break and the faster the reaction
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7
Q

is water a good or poor nucleophile

A
  • poor nucleophile but it can react slowly with halogenoalkanes in substitution reactions
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8
Q

nucleophilic substitution with aqueous hydroxide ions
- change in group
- reagent
- conditions
- mechanism
- role of reagent

A
  • 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-
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9
Q

SN2 mechanism for halogenoalkanes

A
  • primary halogenoalkane
  • show the transition state
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10
Q

SN1 mechanism

A
  • tertiary halogenoalkanes
  • first the halogen breaks away from the halogenoalkane to for a carbocation intermediate
  • the OH- nucleophile then attacks the positive carbon
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11
Q

nucelophilic substitution with ammonia
- change in group
- reagent
- conditions
- mechanism
- role of reagent

A
  • 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
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12
Q

elimination with alcoholic hydroxide ions
- change in group
- reagent
- conditions
- mechanism
- role of reagent

A
  • change in group: halogenoalkane to alkene
  • reagent: potassium/sodium hydroxide
  • conditions: in ethanol; heat
  • mechanism: elimination
  • role of reagent: base, OH-
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13
Q

hydrolysis reaction with aqueous silver nitrate

A
  • 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
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14
Q

rates of hydrolysis of iodo, bromo and chloroalkanes - fastest to slowest & colour of precipitate

A
  • AgI - yellow precipitate
  • AgBr - cream precipitate
  • AgCl - white precipitate
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15
Q

rates of hydrolysis of primary, secondary & tertiary halogenoalkanes

A
  • 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
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16
Q

trend in reactivity of primary, secondary & tertiary halogenoalkanes

A
  • primary halogenoalkanes have the highest boiling point and therefore are the least reactive
  • as more carbon atoms are connected to the carbon atom the halogen is connected to, the more reactive the molecule is.
  • reactivity goes tertiary > secondary > primary (most to least)
17
Q

trend in reactivity of chlor, bromo & iodoalkanes in terms of bond enthalpy

A
  • iodoalkanes have the highest melting and boiling points due to greater London forces
  • C-I bonds are weakest hence why iodoalkanes are the most reactive