Chapter 15 - Haloalkanes Flashcards
The chemistry of the haloalkanes, Organohalogen compounds in the environment.
What are nucleophiles?
Species that donate a lone pair of electrons.
Give three examples of nucleophiles
Hydroxide ions ( OH-) Water molecules Ammonia molecules (NH3)
When a haloalkane reacts with a nucleophile, what is the name of the reaction mechanism?
Nucleophilic substitution
What is hydrolysis?
A chemical reaction involving water or aqueous hydroxide that causes the breaking of a bond in a molecule.
Describe the nucleophilic substitution reaction for the hydrolysis of a haloalkane
OH- approaches carbon bonded to halogen on opposite side to halogen
This minimises repulsion between nucleophile and halogen’s dipole
Lone pair of electrons on OH attracted to and donated to carbon atom
New bond formed betwen oxygen and carbon atom
Carbon-halogen bond breaks
Alcohol and halide ion formed
Describe the conditions for the hydrolysis of haloalkanes
Using aqueous sodium hydroxide and is heated under reflux.
What determines how fast a specific carbon-halogen bond will break?
Bond enthalpy
Which halogenoalkane will react the fastest and why?
Iodoalkanes because C-I bonds are the weakest so require less energy to break.
How can hydrolysis of haloalkanes be compared to one another?
Perform the reaction in the presence of aqueous silver nitrate and record the time taken to form a precipitate.
What would the results show?
Chloroalkanes react slowest
Iodoalkanes react fastest
Therefore rate of hydrolysis increases as the strength of the carbon-halogen bond decreases.
How does primary, secondary or tertiary halogenoalkane status affect rate of hydrolysis?
Tertiary reacts the fastest because the intermediary carbocation that is formed is much more stable than a primary carbocation.
How do CFCs deplete the ozone layer?
UV radiation provides sufficient energy for the carbon-halogen bond to break by homolytic fission forming radicals.
What other radicals are responsible for ozone depletion?
Nitrogen oxide radicals
What are the different prefixes for the halogens in a a haloalkane?
bromine- bromo
chlorine- chloro
iodine-iodo
fluorene - fluro
how do you name haloalkanes?
add prefix of halogen to the longest chain. when two or more halogens are listed ts in alphabetical order
what are primary secondary and tertiary haloalkanes?
