Haloalkanes Flashcards
What is a Haloalkane
these are saturated organic compounds that contain carbon atoms and at least one halogen atom
What is a primary haloalkane
this is a haloalkane that has the halogen atom at the end of a chain
Explain the electronegativity of a haloalkane
this is when there is a large difference in the electronegatives of carbon and halogens therefore the carbon-halogen bond in haloakanes are polar, the electrons in the C-X bonds spend more time near the halogen atom than the carbon atom, this results in a slightly positive charge on the carbon atom and a slightly negative charge on the halogen atom
What happens to the slightly positive carbon atom in the haloalkane
- the slightly positive carbon atom is attacked by atoms molecules or ions that have a partial or full negative charge like H2O, OH-, NH3, these species are called nucleophiles and they are electron pair donors
DRAW A NUCLEOPHILLE ATTACKING A HALOALKANE
PG 205
What are the factors that effect nucleophile reactions
- strength of the C-X bond, going down the halogen group in the periodic table the atom gets larger, this means that their bonding electrons are further away from the nuclei and there is stronger shielding therefore there are lower mean bond enthalpies and the C-X bonds are easier to break, the higher the mean bond enthalpy the less likely that the halogen will react in a nucleophilic substitution reaction
- the polarity of the C-X bodn, fluorine is the most electronegative element so electronegativity decreases going down the group therefore the polarity of the C-X bond decreases going down the group, the molecules with the highest polarity are more likely to react
What is nucleophilic substitution
- this is a reaction where an atom or group of atoms are exchanged for a nucleophile, nucleophile is attracted to the partial positive charge on the carbon atom and donates its lone pair of electrons to form a new covalent bond
What is hydrolysis reaction
- neutrophilic substitution reaction
- water is the reactant that provides the hydroxide ions that act as nucleophiles
- if water is used one of the H-O bonds undergo hetrolytic fission to produce the nucleophile OH-
- This species attacks the electron deficient carbon atom in the haloalkane molecule
- then the nucleophile bonds to the haloalkane molecule and undergoes heterolytic fission to produce a halide ion
DRAW THE HYDROLYSIS OF 1-IODOPROPANE
DRAW IT
How do you measure the rate of hydrolysis
- change in concentration of a reactant or product in a given time
- halide ions form a colour precipitate of silver halide when acidified silver nitrate is added
What is the most important factor of the hydrolysis of primary alcohol
bond enthalphy
- the C-CL bond is the most polar in the investigation described above and therefore should be the most attractive to the nucleophilic attack, but because of the high C-CL bond enthalpy chloroalkanes have the lowest rate of hydrolysis
- the least polar and least attractive C-I group has a higher rate of hydrolysis because the bond is weaker and easier to break
how is an alcohol made from a haloalkane
- the haloalkane is heated under reflux with an aqueous solution containing hydroxide ions an alcohol is made, this is a nucleophilic substitution reaction and hydrolysis
- rate of reaction is dater than using water
- DRAW THE HYDROLYSIS OF 1-CHLRORPROPANE WITH SODIUM HYDROXIDE
What are chloroflurocarbons
class of organic compounds that contain chlorine and fluorine atoms
Why were chloroflurocarbons used
- non-toxic
- non reactive
What were chloroflurocarbons used for
- used in fire fighting equipment - non-flammable
- aviation industry
- aerosols
- refrigerants
- plastics like polystyrene - did not react with the polymer,
