B3.3 - Alkenes
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Define alkenes.
alkenes are unsaturated hydrocarbons
What type of bonds do alkenes have?
pi bonds sigma bonds
Define pi bonds
sideways overlap of p-orbitals
Define sigma bonds
end on end overlap of two s-orbitals
What happens around the pi bond?
pi bond locks two carbon atoms in position and prevents them from rotating around he double bond
Explain the term stereoisomers.
have the same structural formula but a different arrangement in space
Explain the term E isomerism.
priority groups are on the opposite sides of the double bond
Explain the term Z isomerism.
priority groups are on the same side of the double bond
Explain the term cis isomers.
groups that are identical on both carbons are on the same side of the carbon bond
Explain the term trans isomers.
groups that are identical on both carbons, are on opposite sides of the double bond
How to identify E/Z isomers?
z - priority groups are on the same side e - priority groups are on alternative sides
Why do alkenes have a higher reactivity?
presence of pi bonds are weaker than sigma bonds
Define the term electrophile.
electron pair acceptor
What type of reactions do alkenes undergo?
electrophile addition
What is the general formula of alkenes?
CnH2n
Define the term cyclic alkenes.
carbon chain is joined at either end to form a ring
What functional group do alkenes have?
C=C
What is a double bond?
a double bond is a sigma bond and pi bond –> when s and p orbitals overlap - sigma or pi bonds
What are the conditions required for addition reaction with hydrogen
Nickel catalyst 150 degrees Celsius
What type of redox reaction occurs during an addition reaction of hydrogen?
ethene gains hydrogen –> reduction
What are the products of an addition reaction with halogen?
dihalogenalkane products
What are the conditions for the addition reaction with steam?
H3PO4(aq) catalyst temperature above 100 degrees celsius
Show the mechanism of electrophilic addition in alkenes: ethene + bromine
check diagram.
What is meant by the term priority group?
priority groups are the groups with the highest atomic number