Bonding, Alkenes, Isomers Flashcards
What are the two types of bonds?
Pi and Sigma bonds
What is more common Pi or Sigma?
Sigma bonds
What is a sigma bond?
Sigma bonds are the strongest type of covalent bond. All single bonds and the first part of double or triple bonds are sigma bonds
What is a Pi bond?
The second and third part of a triple bond or the second part of a double bond. The Pi bond is not directly between the nuclei so is weaker than a Sigma bond.
What do the solid and dashed wedges represent when it comes to representing a 3D molecule
-wedges are the bonds going away from the plane of the paper
-dashes are the bonds coming towards the plane of the paper
How does Ethene become 1,2-dibromoethane?
Through electrophilic addition at room temperature and pressure when Bromine (aq) is added to ethene
How does ethene become 1chloroethane when HCl (aq) is added?
Through electrophilic addition under RTP and the addition of HCl (aq)
What two ways does ethene become ethane?
- Through addition with an Ni catalyst and H2 (g) at High temperature and pressure
- With a Pt catalyst and H2 (g) at room temperature and pressure
How does ethene become ethanol?
Through electrophilic addition with the H3PO4 and H2O (g) at high temperature and pressure
Describe alkenes reactions with halogens
Alkenes react with halogens at RTP.
Describe the Bromine test for halogens
- add a few drops of bromine water Br2(aq) to an alkene and shake well
- if the compound contains a carbon carbon double bond (unsaturated) there will be a colour change from orange to colourless
Describe the electrophilic addition mechanism
- The partially positive bromine atom accepts a pair of electrons from the carbon carbon double bond
- The Br-Br bond breaks
- This leaves a carbocation intermediate which is unstable and quickly reacts with the Br- from the broken Br-Br bond
The final product is formed
Define electrophile
An electrophile is a positive ion or molecule with a partially positive region which is attracted to a negative region in a molecule, which reacts by accepting a pair of electrons forming a covalent bond.
Define addition reaction
Addition reactions are when 2 molecules react to give just 1 product molecule (by combining together)
What would happen if an unsymmetrical alkene was used in an electrophilic addition reaction (like propene)?
There would be two products on two/ or more different carbons
How can converting an alkene into an alkane be used?
- to find out how many double bonds an alkene has
- hydrogenation of vegetable oils to convert them into margarine since carbon carbon bonds have a higher mp than carbon carbon double bonds
What are the two types of isomerism?
-structural isomers molecules with the same molecular formula but different structural formulas
-steroisomerism molecules with the same molecular formula but atoms point a different way in space (E/Z isomerism)
MAGIC SENTENCE
What is required for a molecule to have E/Z isomerism?
- a carbon carbon double bond which cannot rotate
- each carbon in the carbon carbon double bond must be bonded to 2 different atoms or groups
