3.3 Halogenoalkanes Flashcards
What is the termination step in free radical substitution, use methane & chlorine as an example
Where two radicals react together
Define a free radical
Species with an unpaired electron
Write an equation for each of the following steps in the mechanism for the reaction of chloromethane with chlorine to form dichloromethane
Haloalkanes produced from free radical substitution can react again with another halogen and undergo further substitution. How to prevent further substitution
Use excess alkane
What are CFCs, state what they cause
Haloalkanes that contain both chlorine and fluorine
They cause depletion of ozone layer
Write three equations to show how trichlorofluoromethane is involved in damaging the ozone layer
Why does fluoroethane not lead to the depletion of ozone
Doesn’t contain a chlorine
C-F bonds are strong and do not break
Define a nucleophile
An electron-pair donor
The different nucleophiles that react with haloalkanes in nucleophilic substitution
Draw mechanism for nucleophilic substitution with NH3, CN and OH. Use bromoethane
Reagent and conditions for nucleophilic substitution with OH^-
Reagent : NaOH or KOH
Conditions : aqueous solvent
Reagents and conditions for nucleophilic substitution by CN^-
Reagent : KCN
Conditions : water and ethanolic solvent
Reagent and conditions for nucleophilic substitution by NH3
Reagents : Excess NH3
Conditions : Ethanol solvent, heat and pressure
What is rate of a reaction equal to
1 / time
Describe method for hydrolysis
Reasons for different rates of hydrolysis
As bond enthalpy decreases, it is easier to break C - halogen bond
Weaker the bond, the faster the rate
Name of mechanism from haloalkane to alkene
Reagents :
Conditions :
Electrophilic addition
Reagents : NaOH or KOH
conditions : hot & ethanolic solvent
Outline eliminations for 2-chlorobutane and draw all possible products
State use of CFC’S
They are used as refrigerators
D
Initiation step for CH3F in free radical substitution
F2 -> .2F
State conditions necessary for free radical substitution
UV light
High temperature
Linked to free radical substitution
C2H6 + 6Br2 -> C2Br6 + 6HBr
State why ultraviolet light is needed in free radical substitution, use chlorine as an example
Provides enough energy to break covalent bonds in chlorine to form free radicals
