Alkenes Flashcards
What is a Z stereoisomers
On ‘Z’ same side of the double bond
What is an E stereoisomers
On ‘E’ither side of the double bond
What are alkanes
General formula CnH2n
Bonds between each carbon and two other molecules are called sigma bonds
Remaining two electrons shared in a pi bond in which the electrons are delocalised - weaker bond
Electrons have a high electron density making them quite reactive
How Unsaturation tested for
Alkene is shook with orange bromine water
Solution turns from orange to colourless
Bromine is added across the double bond to form colourless dibromoalkane through electrophilic addition
What happens in electrophilic substitution
C-C double bond is attacked by electrophiles
H-Br, H-OSO3H, H-H or Br-Br
Electrons move from the double bond to the electrophile giving the carbon atom a positive charge allowing a halogen ion to react
What happens during steam hydration of ethene
Used industrially to produce ethanol Ethene is hydrated by steam at 300 degrees and a pressure of 60atm Solid phosphoric(V) acid catalyst Reversible reaction Low yield Can recycle unreacted ethene gas
How are alkenes hydrated
Reacted with water in the presence of cold concentrated sulphuric acid to produce an alcohol
H-OSO3H
Forms an intermediate
Sulphuric acid is a final product as it is never used up and acts as a catalyst
What halogens during addition polymerisation
Many alkene monomers react together to form a long chain with a repeating unit
What are the properties of poly(alkenes)
Saturated and unreactive
Resist attacks by acids and bases
Longer chains have stronger van der Waals
Chains with fewer branches pack closer together and have stronger van der Waals
What is low density poly(ethene) used for
Soft and flexible
Plastic bags and bottles
What is poly(propene) used for
Tough and strong
Bottle crates
Rope
How do unsymmetrical alkenes form
When a small molecule is added to an alkene, there may be a choice of products. This will occur if the alkene is unsymmetrical, forming a carbocation
The most stable carbocation would form in preference but some other carbocation would also form as a minor product
Tertiary carbocations are more stable than primary and secondary
Define markovnikovs rule
When an electrophile adds to an unsymmetrical alkenes carbon double bond, the most stable carbocation will form as intermediate
Define stereoisomers
Compounds with the same structural formula but a different arrangement in space
