Organic Chemistry: Alkenes Flashcards
what is a sigma bond?
overlap of orbitals directly between the bonding atoms
what is a pi bond?
formed by the sideways overlap of adjacent p orbitals above and below the bonding C atoms
what are stereoisomers?
compounds with the same structural formula but with different arrangements of the atoms in 3 dimensional space
what are cahn-ingold-prelog rules?
- the prefix e- or z- is based of the atomic numbers of the atoms
- e-: the atoms with the highest atomic number are on opposite sides
- z-: the atoms with the highest atomic number are on the same side of the double bond
What is e/z isomerism?
e-: the atom with highest atomic number are on opposite sides
z-: the atom with the highest atomic number are on the same side
What is cis/trans isomerism?
- cis: the same group attached is on the same side of the bond
- trans: the same group attached is on opposite sides of bond
what are the 3 types of reaction for alkenes?
- combustion
- electrophilic addition
- addition polymerisation
why is the combustion of alkenes unusual?
lots of other uses due to their reactivity
what is the reaction to go from an unsaturated alkene to saturated alkane?
- addition of hydrogen
- Nickel catalyst
- 150 degrees celsuis
what is addition of halogens to alkenes called?
halogenation - makes a di-substitued haloalkane
how do you test for alkenes?
bromine water added to alkene - Br2(aq) - orange to colourless
what does the addition of hydrogen halides to alkenes form?
haloalkane
why is the addition of hydrogen halide to alkenes a possible problem?
- alkenes are unsymmetrical
- so a mixture of products are usually formed
what is the reaction of an alkene with steam?
alkene + steam –> alcohol
what is the formula for steam?
H2O(g)
what acid catalyst is used when alkenes react with steam?
H3PO4 - phosphoric acid
what are biodegradable polymers?
- made from natural materials
- reduce reliance on crude oil
- naturally decompose
what are photodegradable polymers?
- designed to contain bonds that are weakened by absorbing light - produces reactive radicals
what type of rotation do pi bonds have?
restricted rotation
what shape are alkenes?
- trigonal planar, 120 around each carbon in C=C of alkenes
what are alkenes?
- unsaturated hydrocarbons containing a C=C bond comprising a pi bond and a sigma bond
what impacts the reactivity of alkenes?
relatively low bond enthalpy of the pi bonds
what are the differences between pi bonds and sigma bonds?
- pi bonds are above and below bonding atoms whereas sigma bonds are between the bonding atoms
- pi bonds have sideways overlap whereas sigma bonds have direct overlap
- pi bond has lower bond enthalpy than sigma bond
what are advantages of using polymers?
- combustion for energy production
- use as an organic feedstock
- removal of toxic waste products
why may a compound not have E/Z isomers?
one carbon atom in the double bond is attached to two groups which are identical
why can polymers be used to remove toxic waste products (example)?
- removal of HCl formed during disposal by combustion of halogenated plastics
- e.g PVC
how can polymers be used as an organic feed stock?
- production of plastics and other organic chemicals
what does the monomer unit of alkenes in addition polymerisation?
- contains the double bond
- has an ‘n’ at the front of the molecule
what does the repeat unit of alkenes in a edition polymerisation look like?
- has the ‘n’ at the bottom right of the molecule
- has square brackets
- lines that extend out of the square brackets
why are biodegradable polymers good?
- they leave no visible or toxic residues
