MODULE 4: Haloalkanes
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Define the term ‘nucleophile’
A nucleophile is an atom or a group of atoms that has a partial negative or fully negative that donated a lone pair of electrons (hydroxide ions, ammonia molecules)
What are some of the properties of haloalkanes?
Polar carbon-halogen bond
What is hydroylsis?
A chemical reaction involving water or an aqueous solution with hydroxide ions that causes breaking of bonds in a molecule
What is another name we can call hydrolysis of a haloalkane and why?
Nucleophilic substitution as hydroxide ions are nucleophiles
What reagent is used in nucleophillic substitution of haloalkanes and what product is formed?
Aqueous sodium hydroxide and it forms an alcohol
What is carbon-halogen bond strength?
Energy required to break a carbon-halogen covalent bond due to ‘bond length’
Apply carbon-halogen bond strength to hydrolysis of haloalkanes
Fluorine’s bond cannot be broken due to the very high bond enthalpy, then as you move down group 17 the bond enthalpy decreases (so iodine’s bond is very easy to break)
How can rate of haloalkane hydrolysis be measured?
Time how long precipitate takes to form in halide test (sodium hydroxide then silver nitrate added)
What would the predicted outcome be for the rate haloalkane hydrolysis?
Fluorine does not produce a precipitate, then as you move down group 17 the rate of hydrolysis increases
What are some of the uses for organohalogen compounds?
Flame retardants, solvents, making polymers
What is the Ozone layer?
A layer of gas in the atmosphere that contains a chemical called ozone that absorbs UV radiation and only allowing a small amount of it to hit Earth
What are the risks of UV radiation?
Genetic damage and skin cancer
How is ozone formed by UV radiations in equation form?
O₂ -> 2O O₂ + O ⇌ O₃
What are CFCs and how were they used?
Chlorofluorocarbons, aerosol propellants. Thought to have had a very strong bond, but later found out that bond destabilised in the stratosphere due to UV radiation
Show the equations for how CFCs deplete ozone
CF₂Cl₂ -> CF₂Cl· + Cl· Cl· + O₃ -> Cl· + O₂ ClO· + O -> Cl· + O₂
What chemical, other than CFCs, deplete ozone?
Nitrogen oxide radicals