MODULE 4: Alkenes
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What is the bond angle around a double bonded carbon?
120 degrees
What is stereoisomerism?
Isomers that have the same structural formula but a different arrangement in space
What are the different types of stereoisomerism?
EZ isomerism and cis-trans isomerism
Why does stereoisomerism occur?
Lack of movement around a double bond (due to the pi bond)
What is EZ isomerism?
Stereoisomerism that includes a carbon-carbon double bond and different groups attached to each carbon of the double bond
What is cis-trans isomerism?
Stereoisomerism that includes a carbon-carbon double bond and one of the attached groups must be the same
How do you identify cis-trans and EZ isomerism?
Cis and Z = same side Trans and E = different sides
What is the Cahn-Ingold-Prelog rules?
Atoms/groups of atoms attached to carbons in a double bond are placed in priority of ascending atomic number (then after that, EZ isomerism applies)
Why are alkenes more reactive alkanes?
Because the bond enthalpy of the pi bond is much lower than the bond enthalpy of the sigma bond
How can you test for an alkene?
Add bromine solution to a sample, if sample goes from brown to colourless then alkene present
What addition reactions do alkenes undergo?
Hydrogenation, halogenation, hydrogen halides, hydration
What is an electrophile?
An atom/group of atoms with a partial or full positive charge that is attracted to electrons
What is electrophilic addition?
An addition reaction involving an electrophile
What do curly arrows represent?
The movement of a pair of electrons
What is Markovnikoff’s law?
In an addition reaction, a hydrogen atom will join the bond with the most hydrogens and least carbons attached (forming a majority and minority product)
Why does Markovnikoff’s law occur?
Due to carbocation stability
What is addition polymerisation?
When alkenes become long chains of saturated polymers using high temperatures, pressures and a catalyst
What are the positives of using polymers?
Available, cheap, more convenient to use, unreactive (for storage)
What are the negatives of using polymers?
Non-biodegradable, dangerous chemicals released when recycled/burnt
What are the different types of recycling?
PVC recycling, using them as fuel, feedstock recycling
What are the two types of bioplastics?
Biodegradable polymers and photodegradable polymers
What are biodegradable polymers?
Polymers made of starch or cellulose that can be broken down by microorganisms into water, carbon dioxide and biological compounds
What are photodegradable polymers?
Polymers made of oil-based polymers that has weak bonds that can be broken down by absorbing sunlight