Alkenes Flashcards
What are alkenes?
Unsaturated hydrocarbons, meaning they contain at least one multiple bond between carbon atoms which in an alkene is a C to C double bond.
What is the general formula of alkenes?
CNH2N
What is a C to C double bond made up of?
-A sigma bond formed directly between two carbon atoms by the head-on single overlap of orbitals directly between bonding atoms
-A pie bond formed by the double sideways overlap of p-orbitals above and below the bonding atoms
What is the shape around each carbon?
Trigonal Planar, because there are three bonding regions of electron density around each of the carbon atoms that repel equally to each other creating a bond angle of 120.
What is the rotation around the C to C double bond?
Restricted.
What are sterioisomers?
Compounds with the same structural formula but with different arrangement of atoms in space.
What is the criteria for sterioisomers?
-must have C to C double bond as it cannot rotate
-each carbon must have two different groups attached to it
What is a Z isomer?
Where groups of higher priority are on the same side of the double bond.
What is an E isomer?
Where groups of higher priority are on diagonally opposite sides of the double bond.
Which atoms have the highest priority?
Those with higher atomic numbers.
What is the criteria for Cis-Trans sterioisomerism?
-must have C to C double bond as it cannot rotate
-each carbon must have two different groups attached
-two groups on the C to C double bond must be identical
What is a Trans isomer?
An E isomer.
What is a Cis isomer?
A Z isomer.
What reactions do alkenes undergo?
Electrophilic addition.
What are the conditions and reagents needed to turn an alkene into an alkane?
-Hydrogen gas
-Nickel catalyst, 150 degrees Celsius
What reagents/conditions are needed to turn an alkene into a dibromo alkane?
-room temperature
-Br2
What reagents/conditions are needed to turn an alkene into a halide alkane?
-hydrogen halide
-room temperature
What reagents/conditions are needed to turn an alkene into an alcohol?
-steam/H2O
-concentrated phosphoric acid, high temperature, high pressure
What is an electoophile?
An electron pair acceptor.
What is the most stable carbocation?
Tertiary.
How do you decide which is the major/minor product in an electrophilic addition reaction with an unsymmetrical alkene e.g. propane?
The major product is the one which has the most most directly bonded alkyl groups attached
MINOR
-primary
-secondary
-tertiary
MAJOR
What is addition polymerisation of alkenes?
Alkene monomers join together to from a long, saturated molecule called an addition polymer.
What reagents/conditions are needed for addition polymerisation of an alkene?
-alkene monomer
-high temperature and pressure, catalyst
What are problems with the disposal of addition polymers?
-non biodegradable
-incineration produces toxic gases e.g., HCl
What are benefits of processing waste addition polymers?
-combustion for energy production
-removal of toxic waste products
-used in organic feedstock for the production of plastics and other organic chemicals
What is the role of chemists in minimising environmental damage?
-develop biodegradable polymers
-develop photodegradable polymers(bonds that are weakened by light)
-use of an alkaline scrubber to neutralise HCl gas produced when incinerated
