(2) Alkenes Flashcards
Define an alkene.
Unsaturated hydrocarbon containing at least one C=C double bond.
Why are alkenes more reactive than alkanes?
- the double bond has a high electron density it makes alkenes susceptible to reactions with molecules which have positive charges (electrophiles)
What is the formula for alkenes?
CnH2n
Why don’t double bonds rotate?
- Double bonds consist of one sigma bond and one pi bond.
- Since the pi bonds are bonded sideways and are perpendicular to the plane of the sigma bonds
What are structural isomers?
- molecules which have same molecular formula but different structural formula
What are stereoisomers?
-molecules which have the same structural formula but have different arrangement of atoms in space.
What are position isomers of alkenes?
isomers have different positions of the double bond in the hydrocarbon chain.
the longer the chain, the more isomers there are.
What are geometric isomers?
- A C=C bond with restricted rotation
- each carbon in the C=C double bond must have 2 diff groups attached to it
What is an E isomer?
- highest priority groups on opposite sides of the carbon-carbon double bond.
What is a Z isomer?
high priority groups on same side of double bond
What are the physical properties of alkenes?
- melting and boiling point of alkanes increase as chain length increase as van der Waals forces get larger
- alkanes are insoluble in water
Why are double bonds stronger than single bonds?
- because it has an area of high electron density which is susceptible to attack by electrophiles
Why are alkenes rarely used as fuels?
- because C=C means it is likely incomplete combustion will occur, releasing less energy and more useful
Which is the most stable carbocation?
Tertiary.
What is the positive inductive effect.
- ability of alkyl group to release electron density through a covalent bond
