Alkenes Flashcards
Describe the structure of alkenes?
- unsaturated hydrocarbons
- their general formula is CnH2n
What is a sigma bond?
The overlap of two orbitals consisting of a pair of electrons
What is a pi bond?
- the overlap of two p orbitals
Explain the bonds in the double bond of alkenes
- three out of four electrons are used in three sigma bonds to other atoms, this leaves one electron in a p oribtal
- this forms a pi bond as the p orbitals from each carbons overlap
What does the P orbital make alkenes do
The pi bond prevents rotation around the double bond
What is the shape around a double bond
There are three areas of electron density, these repel causing a bond angle of 120 degrees
Define stereoisomers
Compounds with the same structural formula but with different arrangements of atoms in space
Why do stereoisomers exist?
You cant rotate around the carbon double bond
What conditions must an alkene meet to have stereoisomers?
- a double carbon to carbon bond
- different groups attached to each carbon atom of the double bond
What is an E isomer?
- if the atoms with the highest atomic number are on opposite sides
What is a Z isomer?
Used when atoms with the highest atomic number are attached on the same side of the bond
Who made these priority rules?
Cahn - Ingold - prelog rules
What are cis - trans isomers?
Special cases of E/Z isomers where the two carbon atoms within a double bond have the same group
What are cis/trans isomers equivalent to ?
E = trans
Z = Cis
What are the three reactions that alkenes undergo?
- Combustion
- electrophilic addition
- addition polymerisation