2.5 Hydrocarbons Flashcards
What is the equation for combustion of ethane?
C2H6 + 3 1/2 O2 —> 2CO2 + 3H2O
What is the equation for the incomplete combustion of ethane?
C2H6 + 2 1/2 02 —-> 2CO + 3H20
What is halogenation?
a reaction between an organic compound and any halogen (member of group 7)
What are the three steps of halogenation?
- Initiation
- Propagation
- Termination
What is a radical?
a highly reactive species with an unpaired electron.
What occurs in the initiation stage of halogenation between an example of methane and chlorine?
Ultraviolet light has sufficient energy to break the Cl–Cl bond within Cl2 (homolytic fission thus both Cls receives one of the bond electrons), as a result radicals are formed.
What occurs in the propagation stage of halogenation of an example of methane and chlorine?
A propagation reaction uses a radical as a reactant and then forms a radical as a product. This means that the reaction continues. It is therefor called a chain reaction.
What occurs in the termination stage of halogenation of an example of methane and chlorine?
The propagation step continues until two radicals meet, then the reaction stops (termination stage)
This stage the two radicals create a compound with no radical.
Use a whiteboard and write out the free radical substitution mechanism.
of chlorine
Discuss the structures of alkenes:
They are unsaturated so contain a double bond and are thus much more reactive than alkanes.
Discuss ethene:
4 electrons available for bonding, three are normal covalent sigma bonds using both the carbons s orbital electrons and 1 p orbital. This means there are three bond pairs of electrons around each carbon resulting in a trigonal planar shape with bond angles of 120 degrees. The overlapping p bond creates pie bonds above and below the plane of the molecule which restrics the movement creating E-Z isomers.
When does E-Z isomerism occur?
In alkenes where each end of the C=C has two different groups bonded to it.
Why are alkenes susceptible to electrophilic attack?
as they have a pair of electrons in a pie orbital that makes them susceptible to attack from an electrophile (+)
What is an electrophile?
An electron deficient species that can accept a lone pair of electrons.
What is heterolytic bond fission?
When a bond breaks and one of the bonded atoms receive both electrons thus ions are formed.
Write the mechanism of electrophilic addition of HBr to ethene.
which is the major product of the electrophilic addition of propene, 2-bromopropane or 1-bromopropane and why?
2-bromopropane as the cation releases a delta plus that can spread around so position 2 has better potential spread than position 1 thus making it more STABLE. (the cations stability goes: primary<secondary<tertiary)
What is the test for alkenes?
Bromine water is used and if alkenes are present it goes from brown to colourless.
What is hydrogenation?
Alkene + hydrogen with a nickel catalyst to make saturates oils to make butter substitues.
Name three useful polymers:
- polypropene for food containers
- polychloroethene for water pipes
- polyphenylethene or polystyrene is used for packaging.
