13.1 The properties of the alkenes
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What are alkenes
Unsaturated hydrocarbons Contain at least one carbon to carbon double bond
What is the general formula for the aliphatic alkenes that contain one double bond
CnH2n
What is the general formula for branched alkenes
CnH2n
Do cyclic alkenes and alkenes with more than one double bond follow the CnH2n general formula
NONONO
How are the carbon atoms bonded
Three of the four electrons are used in three σ- bonds; one to the other carbon atom of the double bond and the other two to two other atoms leaving one not involved in sigma bonds This electron is in a p-orbital, a π-bond
How is a π-bond formed
By the sideways overlap of two p-orbitals, one from each carbon atom of the double bond Each carbon atom contributes one electron to the electron pair in the π-bond. The π-electron density is concentrated above and below the line joining the nuclei of the bonding atoms
What does a V-bond do
Locks the two carbon atoms in position and prevents them from rotating around the double bond. Makes the geometry of the alkenes different from that of the alkanes where rotation is possible around every atom
What is the shape around each of the carbon atoms in the double bond
Trigonal planar
Why is the shape around each of the carbon atoms in the double bond trigonal planar
There are three regions of electron density around each of the carbon atoms The three regions repel each other as far apart as possible so bond angle is 120 All of the atoms are in the same place
What makes flamingos pink
Alkenes Flamingos eat algae and crustaceans containing carotenoids Enzymes in liver convert these into pink and orange pigments deposited in feathers