Alkenes Flashcards
How do you show a double bond when naming an alkene
put the numbers of wherever a double bond occurs, in between the longest carbon chain, eg. “But”. And “ene”
Explain in terms of electron orbital overlap, how C-C single bonds differ from C=C double bonds?
Single bonds form from the end-on overlap of atomic orbitals, producing a sigma bond
The second bond in a double bond is produced by the sideways overlap of 2 p atomic orbitals, to make a pi bond
Single/sigma bonds are free to rotate, pi bonds cannot rotate, as this would break the overlap of the p orbitals
Where do the electrons exist in pi bonding?
Above and bellow the plane of the atoms
What’s stronger the sigma bond or pi bond?
sigma bond, because in a pi bond the electron density is bellow and above the plane of the molecule, whilst the electron density is directly between the 2 carbons in the sigma bond
Will the pi bond or the sigma bond break in a chemical reaction?
pi bond, it’s weaker
What type of bonds does a carbon to carbon triple bond have?
1 sigma bond
2 pi bonds
In what cases is the pi bond stronger than the sigma bond?
Carbon-Oxygen
Carbon-Nitrogen
Define stereoisomerism?
Stereoisomers are molecules that have the same structural formula, but have a different arrangement of atoms in space
How can E/Zisomerism occur?
There is a restricted rotation around a double bond
Each of the atoms of the double bond has 2 different groups attached
How to name with E/Z isomerism?
Functional groups on opposite sides= (E)
Functional groups on same side= (Z)
But these in front of the molecules names
To decide which is the functional group on each side calculate the Mr directly bonded around the carbon (might be a different element eg a halogen) including the carbon. The one with the highest is the functional group
When can Cis or Trans occur?
Is a special case of E/Z isomerism in which 1 of the groups attached to each carbon of the double bond is the same
If these groups on the same side eg higher end, = cis
If these are on opposite groups eg. higher and lower = trans
Explain the addition reaction of ethene with H2?
Requires Ni catalyst, and 150 degrees
Ethane is formed
Explain the addition reaction of ethene with a halogen eg. Cl2?
Room temp and pressure
1,2-dichloroethane formed
Explain the addition reaction of ethene with a halogen bonded to a hydrogen eg. HBR?
Room temp and pressure
Bromoethane formed
Explain the addition reaction of ethene with H2O?
Water is steam
Acid catalyst eg. phosphoric acid
Ethanol formed. OH and H bond to ethane, double bond broken
Colour and solubility of Bromine in water and cyclohexane?
In water:
Orange
Slightly soluble
In cyclohexane:
Orange
Very soluble