Module 4 Flashcards
What is a homologous series?
A family of compounds with similar chemical properties whose successive members differ by the addition of CH2 group.
What is a functional group?
Part of the organic molecule that is largely responsible for the molecules properties.
What are structural isomers?
Compounds with the same molecular formula but different structural formulae
What is homolytic fission ?
Each of the bonded atoms takes one o the shared pair of the electrons.
This forms an atom or group of atom with an unpaired electrons which are called radicals.
What is heterolytic fission?
When one of the bonded atom takes both of the electrons from the bond.
What are alkanes?
-main components of natural gas and crude oil
-mainly used as fuels exploiting their reaction with oxygen to produce heat.
-saturated hydrocarbons containing only sigma bonds.
-each carbon atom is surrounded by four electron pairs in four sigma bonds. This causes a tetrahedral arrangement around each carbon atom.
Trends in Alkanes
As chain length increase, the boiling points increase, this is because the longer chain, the larger surface area and more surface contact between molecules, therefore the greater intermolecular forces to overcome.
The more branched the alkanes are the lower the boiling point as there are fewer London forces, there is less surface contact therefore decreasing the intermolecular forces further.
Reactivity of alkanes in terms of combustion.
They can react with a plentiful supply of oxygen to produce carbon dioxide and water. [combustion].
If there is not enough oxygen however, incomplete combustion may occur, therefore forming carbon monoxide (CO) or carbon itself as soot.
Radical substitution
Reaction of alkanes with halogens :
1. Initiation = homolytic fission occurs breaking the diatomic halogen molecule.
2. Propagation = chain reaction
3. Termination = forming a molecule with all electrons paired.
Limitations of radical substitution.
- further substitution.
- substitutions at different positions in a carbon chain
What are alkanes?
-unsaturated carbons.
- contain double c=c bonds, which are pi bonds. - pi bonds lock the 2 carbon atoms together in position, preventing from rotating around the double bond.
-around each carbon atom the shape is a trigonal planar arrangement.
What are stereoisomers?
Have the same structural formula but a different arrangement of atoms in space.
E/Z - must not have the same atom or group on the same carbon atom.
In cis-trans isomers the only difference is that there MUST be a hydrogen atom on each carbon atom.
How do you know which E or Z isomer?
E/ trans isomer = high priority are facing opposite each other.
Z/ cis isomer = priority are on the same side.
Priority is determined by how high the atomic number is.
Hydrogenation of alkanes
Addition reaction
Alkene is mixed with hydrogen and passed over nickel catalyst at 423 K.
This breaks the double bond, and an alkane is formed.
Propene + H2 — propane
Halogenation of alkanes
A rapid addiction reaction with halogens, Cl, Br or iodine.
[just like H2 but with a halogen instead]
Testing for unsaturation
To identify an alkene you could use the addition reaction involving bromine. When adding bromine water to the solution, if it goes from orange to colourless than an alkene is present.
Hydration reactions of alkanes
Alcohols can be formed from alkanes.
Alkanes reacts with steam in the present of a phosphoric acid analyst [H3PO4].
What is an electrophile?
An atom or molecule that in a chemical reaction accepts an electron pair.
Usually a positive ion or an atom with a partial positive charge.
Electrophilic addition reactions in alkanes
What is Markownikoff’s rule?
That two isomeric products are formed when propene [unsymmetrical alkene] reacts with hydrogen bromine [also unsymmetrical].
It figure out the major product the hydrogen fro the hydrogen bromide must be on the carbon with the highest number of hydrogens. So usually at the end.
Carbocation stability
From least to most stable:
Primary, secondary, tertiary
What is PVC?
Poly[chloroethene]/ poly[vinyl chloride].
It is flexible or rigid. Used in pipes, films and sheeting, ducts and profiles.
Poly(propene) uses
Childrens toys
Packing crates
Guttering
Fibres for ropes
Explain disposing of waste polymers.
Polymers are readily available and cheap, however it easy throwaway advantages has very negative impacts on the environment.
To combat this:
- you can recycles polymers. Chopped into flakes, washed, dried and then melted and used by manufacturers.
- you can use waste polymers as fuel.
- feedstock recycling, where you can reclaim monomers, gases or oil from waste polymers.
Oxidation of alcohols
Primary or secondary alcohols can be oxidised, which is usually potassium dichromate or acidified with dilute sulphuric acid.
If the alcohol is oxidised the orange solution containing dichromate ions is reduced to a green solution containing chromium ions.
Oxidation of primary alcohols
Oxidised and distilled into an aldehyde.
Then ab be further oxidised (2[o]) into a carboxylate acid by reflux.
Oxidation of secondary alcohols
Oxidised under reflux into a ketone.
Dehydration of alcohols
Alcohol is dehydrated into an alkene using phosphoric acid. It is heated under reflux.
Substitution reactions of alcohols.
Can be done hydrogen halides in which they form haloalkanes. The alcohol is heated under reflux with sulfuric acid and a sodium halide where the hydrogen halide is formed.
What are nucleophiles
Atoms or groups that’s are electron pair donors.
Nucleophilic substitution in haloalkanes.
Hydrolysis = involves water or an aqueous solution of hydroxide that cause the breaking of a bond in a molecule.
How to measure the rate of hydrolysis of primary haloalkanes
Carry out the reaction in the presence of aqueous silver nitrate, in which you can measure the amount of precipitate formed of the silver halide. Rate of hydrolysis increase as you go down the group of halogens. As iodine has the weakest carbon-halogen bond.
