Chem Exam Main Topics Flashcards
What is Polymerisation?
When alkenes join together
When alkenes join together, what happens to their double bond?
Their double bond opens up
How do you find the monomer used to make an addition polymer?
You find the repeat unit, add a double bond between the carbon atoms and remove the single bonds from each end
What do all alkenes have?
At least one C=C double bond
What are single covalent bonds in organic molecules?
Sigma bonds
When are sigma bonds formed?
When two orbitals overlap in a straight line, in the space between 2 atoms, giving the highest possible electron density between the 2 atoms
Why are sigma bonds the strongest type of covalent bond?
There is a high electron density between the nuclei so there is strong electrostatic attraction between the nuclei and shared pair of electrons, so there is high bond enthalpy
What is a double bond made up of?
A sigma bond and a pi bond
How is a pi-bond formed?
When 2 lobes of p-orbitals overlap sideways
In a pi-bond, how is the electron density spread out?
Above and below the nuclei
Why do pi-bonds have lower bond enthalpy than sigma bonds?
The electron density in a pi-bond is spread out above and below the nuclei, causing the electrostatic attraction between the nuclei and shared pair of electrons to be weaker in pi-bonds
In alkenes, what does the C=C bond contain?
A pi bond and a sigma bond
What causes alkenes to form sterioisomers?
The restricted motion around the C=C double bond
Ethene is said to be ‘completely planar’, what does this mean?
All the H-C-H bond angles are all the same. The atoms all lie in the same plane
What are sterioisomers?
Molecules which have the same structural formula, but different arrangement in space
When do stereoisomers occur?
When two double bonded carbon atoms each have 2 different groups or atoms attatched to them
What is the ‘E-isomer’?
The isomer which has the same groups positioned across the double bond
What is the ‘Z-isomer’?
The isomer which has the same groups positioned either both above or both below the double bond
What happens to the E/Z system when all the groups are different around the C=C double bond?
You assign each group/atom a number of priority. The 2 atoms/ groups with the highest mass number are labelled 1, whilst the 2 atoms or groups with the lowest mass number are labelled 2.
When do you use the cis-trans naming system?
If the carbon atoms have at least one group in common
When do you use the ‘cis’ naming system?
The the groups are on the same side of the double bond
When do you use the ‘trans’ naming system?
When the same groups are on opposite sides of the double bond
When does the cis-trans naming system not work?
When the carbon atoms have totally different groups attached to them
What happens in an alkene electrophilic reaction?
The alkene double bond opens up and atoms are added to the carbon atoms