Halogenoalkanes Flashcards
What are CFCs used for?
•Short chain CFCs are gases and used in aerosols propellants refrigerators
•Long chain CFCs are used as dry cleaning and de-greasing solvents
What is a primary halogenoalkane?
When there is only one carbon attached to the carbon atom adjoining the halogen
What is a secondary halogenoalkane?
Two carbons attached to the carbon atom adjoining the halogen
What is a tertiary halogenoalkane
Three carbons attached to the carbon atom adjoining the halogen
Describe how boiling points change in a halogenoalkane
- It increases with increased chain length as there are more Van der waals forces
- Haloalkanes have higher boiling points than hydrocarbon chains of similar lengths due to greater relative molecular mass and polarity (dipole dipole)
Describe how bond enthalpy changes in a halogenoalkane
Bond enthalpy decreases as you go down the group
Attractive forces between shared bonding pair and nucleus of halogens is weaker as you go down the group
This causes reactivity to increase as you go down
Bond polarity
The C-X bond in a haloalkane is POLAR because the halogen(X) is more electronegative
Give the general formula of Halogenoalkanes
CnH(2n+1)X
x= haloalkane
Solubility of haloalkanes
•The polar C-X bonds are NOT POLAR ENOUGH TO MAKE THE HALOALKANE SOLUBLE IN WATER
•Main intermolecular forces are van der waals and dipole dipole (no hydrogen bonds)
Why does boiling point decrease when the branching of chains increases
There is less interaction between molecules because they can’t get as close together decreasing the area of contact which weakens VDW forces
Show reactions which show how chlorine atoms catalyse the decomposition of ozone
Cl• + O3 —> ClO• + O2
ClO• + O3 —> Cl• + 2O2
Show the overall reaction for the decomposition of ozone
2O3–> 3O2
Why have CFCs been banned
Beneficial to the environment as they decompose Ozone
Chemists have developed alternative chlorine free compounds
Why is the hole in the ozone layer significant
Ozone absorbs harmful UV radiation and holes in the ozone layer increases the exposure of humans to UV which leads to sunburn, ageing of skin and skin cancer
How does chlorine catalyse the decomposition of ozone?
The UV radiation causes the C-Cl bonds in the CFCs to break homolytically creating a chlorine free radical which reacts to ozone
What are CFCs
Chlorofluorocarbons are haloalkanes containing only chlorine fluorine and carbon
What are the conditions of nucleophilic substitution with OH-
In an aqueous solution and heated under reflux
What are the conditions of nucleophilic substitution with CN^-
Water/Ethanol mix and heated under reflux
Conditions of nucleophilic substitution with NH3
Dissolved in Ethanol and heat under pressure e.g. in a sealed tube
Why does the carbon halogen bond mentally influence the rate of reaction
The carbon halogen bond has to be broken during the reaction. the harder the bond is to break (the higher the bond enthalpy) the slower the haloalkanes reacts
Why does the mechanism of nucleophilic substitution with NH3 require two moles
One acts as a nucleophilic and the other acts as a base
Conditions for the elimination reaction of a haloalkane with sodium or potassium hydroxide
Ethanol and heat under reflux
What happens when a reagent acts as a nucleophilic
it acts as an electron pair sonar and a substitution takes place
What happens When a reagent acts as a base
it acts as a hydrogen ion acceoter and an elimination takes place
