Organics – Alkanes
This is in a plentiful supply of oxygen so the alkane can burn cleanly
This is in limited supply of oxygen which produces carbon monoxide which is toxic
Carbon monoxide
CH4 + Cl2 > CH3Cl + HCl
CH3Cl +Cl2 > CH2Cl2 + HCl
CH2Cl2 + Cl2 > CHCl3 + HCl
CHCl3 + Cl2 > CCl4 + HCl
Any of the hydrogen atoms can be replaced and the reaction continues until all the hydrogen atoms are replaced
Needs to be the in presence of UV light
The mechanism
Initiation
Cl· + Cl· > Cl2
CH3· + CH3· > CH3-CH3
Cl· + CH3· > CH3Cl
- The alkanes are held together by weak London forces, as the molecules get larger, the surface area, the melting and boiling points also rise as the chain increases
- A straight chain will have a larger boiling point compared to an isomer due to having a larger area of contact
- Alkanes are covalently bonded and are hybridised, the s orbital is promoted into the configuration of sp3 which is a more stable molecule. It is also overlapping of the s orbitals of the hydrogen so it is a sigma bond
- Complete combustion
This is in a plentiful supply of oxygen so the alkane can burn cleanly
- Incomplete combustion
This is in limited supply of oxygen which produces carbon monoxide which is toxic
Carbon monoxide
- Combines irreversibly with haemoglobin to form carboxyhaemoglobin
- Prevents oxygen transportation
- Colourless, odourless and very toxic
CH4 + Cl2 > CH3Cl + HCl
CH3Cl +Cl2 > CH2Cl2 + HCl
CH2Cl2 + Cl2 > CHCl3 + HCl
CHCl3 + Cl2 > CCl4 + HCl
Any of the hydrogen atoms can be replaced and the reaction continues until all the hydrogen atoms are replaced
Needs to be the in presence of UV light
The mechanism
Initiation
- The sunlight is needed to start the reaction
- This breaks the Cl-Cl bond
- This is homolytic fission as the molecule splits evenly
- Each chlorine atom produced has a single unpaired electron, a radical
- UV light provides enough energy to allow for the homoloytic fission of the molecule
- A free radical can attack a methane molecule to produce a methyl molecule and hydrogen chloride
- The CH3 radical produced can then attack another chlorine molecule
- In propagation the free radical reacts with a molecule to produce a new molecule and a new free radical
Cl· + Cl· > Cl2
CH3· + CH3· > CH3-CH3
Cl· + CH3· > CH3Cl
- These reactions mop up free radicals, the things causing all the reaction, this terminates the reaction which would go on indefinitely
- Further substitution occurs, producing a variety of products
- Substitution can occur at different positions in the carbon chain