Flashcards in 10.2 Functional Group Chemistry Deck (38):
What reactions to alkanes undergo?
What are the products of complete combustion?
Carbon dioxide and water.
What are the products of incomplete combustion?
Incomplete combustion is when there is a limited supply of oxygen and the reaction produces carbon monoxide, carbon and water.
Why are alkanes unreactive?
There are high strength C-C and C-H bonds.
The C-C and C-H bonds and the overall molecules are essentially non polar.
Whta is a substitution reaction?
One in which one atom or group is replaced by another atom or group.
What are free radicals?
Species (atoms or groups of atoms) with an unpaired electron.
What is homolytic fission?
Where a covalent bond breaks so that one electron goes back to each atom making up the original covalent bond.
How is homolytic fission shown?
With fish hook arrows showing the movement of one electron.
How to alkanes undergo substitution reactions?
In the presence of UV light alkanes undergo substitution reactions with halogens, the mechanism for these reactions is FREE RADICAL SUBSTITUTION.
What are the steps of free radical substitution for the reaction of methane with chlorine?
The first stage is photochemical homiletic fission of the bond between the halogen atoms to produce two free radical:
INITIATION Cl2 ----> 2Cl*
PROPOGATION Cl* + CH4 ----> CH3* + HCl
PROPOGATION CH3* + Cl2 ---> CH3Cl + Cl*
TERMINATION Cl* + Cl* ----> Cl2
TERMINATION Cl* + CH3* ----> CH3Cl
TERMINATION H3C* + CH3* ----> C2H6
The Cl* generated in the second propagation step can go on to react further with another methane molecule so the the cycle of propagation sets starts again - a chain reaction.
Why are alkenes more reactive than alkanes?
Onw component (the pi bond) of the C=C is weaker than a normal C-C single bond.
The double bond (four electrons) attracts electrophiles (reagents attracted to electrons).
What reactions to alkenes undergo?
What happens when alkenes react with halogens?
The double bond opens up and the halogens add on.
What happens when alkenes react with hydrogen?
With a nickel catalyst and 150 degrees Celsius heat, the double bond opens up and hydrogen adds on.
What happens when alkenes react with hydrogen and a halogen eg H-Br?
If heated the double bond opens up and they add on to the molecule.
What happens when alkenes react with water?
With a concentrated sulphuric acid catalyst and heat the double bond opens up and the water adds on.
How can alkenes and alkanes be distinguished form each other?
By shaking them with bromine water.
Alkenes will change from orange to colourless.
Alkanes there will be no change in colour.
What are the conditions needed for alkene to undergo addition polymerisation?
Require high temperature and pressure and maybe a catalyst.
What is the structure put in brackets called?
The repeating unit of the polymer, the basic unit form which the whole polymer can be made up.
How are addition polymers named?
According to the monomer from which they were made.
What is the only group that reacts when the polymerisation reaction occurs?
Only the C=C group reacts, all other groups attached to the C=C are unaffected.
How do you draw or find the repeating unit form part of the polymer chain?
Take any two adjacent Cs in the polymer chain to give the repeating unit.
How can you make the repeating unit the original monomer?
Put a double bond between the 2Cs.
How do alcohols combust in oxygen?
The produce water and carbon dioxide.
How are primary alcohols oxidised?
First to an aldehyde which can be oxidised further to a carboxylic acid.
What are some oxidising agents that can be used?
Acidified dichromate(VI) [Cr2O7^2-/H+] colour change from orange to green.
Acidified manganate(VII) [MnO4^-/H+] colour change from purple to colourless.
How do you obtain the carboxylic acid as the main product from the reaction mixture?
Heat under reflux.
How do you obtain the aldehyde as the main product from the reaction mixture?
Distillation so that as the aldehyde distils off as soon as it is formed since the aldehyde has a lower boiling pint that the alcohol as there is no hydrogen bonding between aldehyde molecules.
How are secondary alcohols oxidised?
Ketones which cannot be oxidised any further.
How are tertiary alcohols oxidised?
Cannot be oxidised.
What is the process of esterification?
When an alcohol is heated with a carboxylic cis in the presence of a small amount of concentrates sulfuric acid as a catalyst and an ester is formed.
What type of reaction is an esterification reaction?
Condenstion reaction - two molecules join together with the elimination of water.
How can you work out the structure of n ester?
Put the OH groups of the alcohol and carboxylic acid together, join the O of the alcohol to the C bearing the C=O and then remove the water.
How do you name esters?
The carbon chain containing the COO group is named as alkanoate and the other carbon chain as an alkyl group.
What is a nucleophile?
Species possessing a lone pair of electron which is attracted to an electron deficient region is a molecules and donates a lone pair of electrons to form a coordinate covalent bond.
Why are halogenoalkanes more reactive than alkanes?
The very electronegative halogen atom makes the C that it is attached to more positive so that it attracts a nucleophile.
What type of reactions to halogenoalkanes undergo?
Nucleophilic substitution reactions, for example when 1-bromopropane is heated with aqueous NaOH the Br is replaced by an OH.