haloalkanes Flashcards
What are haloalkanes
Saturated organic compounds that contain carbon atoms and at least one halogen atom
Are halogenalkanes soluble in water?
- yes
- Halogens are more electronegative than carbon so the carbon-halogen bond is polar
- The positive carbon is electron deficient so it can be attacked by a nucleophile
Do halogenalkanes have a polar bond? Why?
- Yes contain a polar bond
- Halogen has a higher electronegativity than C so halogen-C bond is polar
What type of intermolecular forces do halogens have? Why?
Permanent dipole-dipole and London forces of attraction
C-X bond polarity creates permanent dipoles
When would halogenalkanes have higher boiling points?
- Increased carbon chain length
- Halogen further down group 7
What is the most important factor in determining halogen reactivity?
The strength of the carbon halogen bond
What would bond polarity suggest the order of reactivity would be in haloalkanes?
C-F would be most reactive as most polar bond
What would bond enthalpies suggest the order of reactivity would be?
C-I would be most reactive as it has the lowest bond enthalpy
What is a primary halogen?
The halogen atom is present at the end of the chain
Define nucleophile
Electron pair donor
Give 3 examples of nucleophiles
- OH-
- CN-
- NH3
What is nucleophilic substitution?
A reaction where a nucleophile donates a lone pair of electrons to a partially positive C atom, the partially negative atom leaves molecule and is replaced by nucleophile
What reactant often produces hydroxide ions for hydrolysis?
Water
What fission does water undergo to produce OH-
Heterolytic fission
What are CFCs?
Chlorine-fluoro-carbons, haloalkanes contains C,F and Cl only
What is the problem with CFCs
- Unreactive under normal conditions, they catalyse the breakdown of ozone in the atmosphere via free radical substitution
What is the main function of ozone layer
Provides protection from harmful UV radiation
How do CFCs break the ozone layer down
Free radical substitution
Write an equation for the overall decomposition of ozone into oxygen (O2)
2O3 -> 3O2
How do you produce alcohol from haloalkanes
- By a nucleophilic substitution reaction
- Use a warm aqueous alkali like NaOH to hydrolyse the haloalkane to an alcohol
- The reaction has to occur under reflux
What is needed for the hydrolyzation of haloalkanes to alcohols
Warm aqueous alkali like sodium hydroxide (NaOH) or potassium hydroxide (KOH)
What happens to the reactivity of haloalkenes down group 7?
The reactivity increases
What are the properties of chlorofluorocarbons (CFCs)
- Stable
- Volatile
- Non-flammable
- Non-toxic
Why are holes in the ozone layer harmful
Because they allow more harmful UV radiation to each Earth
What do free nitrogen oxides radicals do?
NO free radicals from nitrogen oxides destory the ozone
How are holes in the ozone layer formed
- CFS in the upper atmosphere absorbs UV radiation and split to form chlorine-free radicals
- These radicals catalyze the destruction of ozone, they destroy ozone molecules and are then regenerated to destroy more ozone
Describe what alternatives to CFCs are used
- HCFCs and HFCs are being used as temporary alternatives until safer products are developed
- Hydrocarbons are used
What are the disadvantages of using HCFCs and HFCs as alternatives to CFCs
- They are broken down in the atmosphere in 10-20 years, they still damage the ozone layer but their damage is smaller than the CFCs
- HFCs and HCFCs are greenhouse gases
What are the advantages of using HFCs over HCFCs
HCFS are also broken down in the atmosphere, unlike HCFCs they don’t contain chlorine so they don’t affect the ozone layer
What did the government do to prevent the use of CFCs internationally?
The Montreal Protocol of 1989 phased out the use of CFCs and other ozone-destroying haloalkanes by the year 2000.
What is the greenhouse effect
It is when various gases in the atmosphere that contain C=O, C-H or O-H bonds are able to absorb infrared radiation and re-emit it in all directions
What are the main greenhouse gases
- Water vapor
- Carbon dioxide
- Methane
What do higher concentrations of greenhouse gases due to industrialization mean to global warming?
Higher concentrations of greenhouse gases mean more heat is being trapped and the Earth is getting warmer (global warming)
Define global warming
Global warming is responsible for recent changes to climates
How are governments working to reduce their greenhouse gas emissions?
- 1997 the Kyoto protocol was signed which means industrialized countries promised to reduce their greenhouse gas emissions to agreed levels, 50% by 2050
- The UK government created policies to use more renewable energy supplies such as wind and solar farms to reduce emission
