Halogenoalkanes Flashcards
what does halogenoalkanes contain ?
saturated hydrocarbon chains with a carbon atom bonded to a halogen atom ( F, CI, Br or I )
what bonds do halogenoalkanes contain ? why ?
polar bonds since the halogens are more electronegative than a carbon atom
- electron density is drawn towards the halogen, forming delta positive and negative regions
how do we make halogenoalkanes ?
ethane + chlorine - >
chloroethane + HCI
condition: UV
how do we make halogenoalkanes ?
ethene + hydrogen bromide - >
bromoethane
physical properties of halogenoalkanes
they have a higher boiling point than their analogous alkane because the polarity of the carbon - halogen bond leads to stronger intermolecular forces
- there are more electrons so London forces are stronger
why are halogen carbon bonds polar ?
due to the greater electronegativity of the halogen atom this leads to a much stronger pd- pd interaction
as alkyl chain length increases what happens to the solubility ?
it decreases
is halogenoalkanes more/ less soluble compared to analogous alkanes ?
more because more similar intermolecular forces with the solvent means greater solubility
what forces makes halogenoalkanes more soluble in water than alkanes
PD - PD forces - must form hydrogen bonds
what is an elimination ?
a reaction which produces an unsaturated product by loss of atoms or groups
what is a base ?
a chemical species with a pair of electrons to remove a hydrogen ion
how are halogenoalkanes usually attacked by ?
nucleophiles
what is hydrolysis ?
a reaction in which a compound is split apart in a reaction with water
what solution is a good test for the presence of halogenoalkanes ?
aqueous silver nitrate
what does AgCI make ?
white
what does AgBr make ?
cream
what does AgI make ?
yellow
in silver chloride, what does the precipitate do in both ammonia (aq) and conc. ammonia ?
- ppt dissolves
- ppt dissolves
in silver bromide, what does the precipitate do in both ammonia (aq) and conc. ammonia ?
- ppt remains
- ppt dissolves
in silver idoide, what does the precipitate do in both ammonia (aq) and conc. ammonia ?
- ppt remains
- ppt remains
testing for haloalkanes
C2H5X (ethanol) + H2O (l) -> C2H5OH (aq) + AgX (s)
comparing the halogen atoms - order them from slowest to fastest
fluorine, chlorine, bromine and iodine
during nucleophilic substitution what bond must break ?
C - halogen bond
how does the rate of hydrolysis become faster ?
the weaker the bond the less energy required to break it
why is ethanol used in the testing of halogenoalkanes ?
solvent
- both haloalkanes and water dissolve in ethanol
Reactant: aqueous potassium hydroxide
formula of attacking species/ nucleophile or base:
conditions:
products:
formula of attacking species/ nucleophile or base: :OH- nucleophile
conditions: warm and aqueous
products: alcohol + halide ion
Reactant: aqueous silver nitrate in ethanol
formula of attacking species/ nucleophile or base:
conditions:
products:
formula of attacking species/ nucleophile or base: :OH2 nucleophile
conditions: warm, acidified silver nitrate
products: alcohol and silver halide precipitate
Reactant: potassium cyanide
formula of attacking species/ nucleophile or base:
conditions:
products:
formula of attacking species/ nucleophile or base: :CN- nucleophile
conditions: heated under reflux in ethanol
products: nitrile and halide ion
Reactant: concentrated ammonia
formula of attacking species/ nucleophile or base:
conditions:
products:
formula of attacking species/ nucleophile or base: :NH3 nucleophile and then base
conditions: ethanol, heat, pressure and sealed tube
products: amine or ammonium salt
Reactant: ethanolic potassium hydroxide
formula of attacking species/ nucleophile or base:
conditions:
products:
formula of attacking species/ nucleophile or base: :OH- base
conditions: heat and ethanol
products: alkene, water and halide ion
