Alkenes

• Addition polymerisation is a type of polymerisation where monomers add to each other to form long chains.
• Alkenes are unsaturated hydrocarbons containing a C=C bond comprising a pi-bond and a sigma-bond with restricted rotation of the pi-bond.
• The extent of unsaturation in a hydrocarbon refers to the number of C=C double bonds it has.
• The chemical test for unsaturation involves adding bromine water to the hydrocarbon.
• A π-bond is formed by the sideways overlap of adjacent p-orbitals above and below the bonding C atoms.
• Alkenes have a trigonal planar shape due to equal repulsion of three bonding centres.
• Alkenes are more reactive than alkanes due to the relatively low bond enthalpy of the π-bond in alkenes compared to the higher bond enthalpy of a σ-bond in an alkane.
• Stereoisomerism is a concept where compounds with the same structural formula but with a different spatial arrangement of atoms are referred to as different stereoisomers.
• E/Z isomerism requires restricted rotation about a double bond and two different groups to be attached to each carbon atom of the C=C group.
• Alkenes with the C=C on C-1 cannot exhibit E/Z isomers because C-1 will have two H atoms on it that are the same.
• To determine if an alkene is E or Z, assign priority to the groups on each C either side of the C=C, if priority groups are on the same side then it's Z.
• To assign priority to groups either side of a C=C using Cahn Ingold priority rules, compare the atoms one at a time starting with C, then any atoms on that C with H's being first in the list.
• If the alkene has a ring, priority can be assigned by looking for a lack of symmetry to find the difference.
• E/Z isomers are named by putting the E or Z at the front of the name followed by a hyphen.
• Cis/trans isomers require two atoms on either side of the C=C to be identical.
• Cis/trans isomers are named by putting the cis or trans at the front of the name followed by a hyphen.
• Four reagents that react with alkenes in addition reactions are hydrogen, halogens, hydrogen halides and steam.
• Addition reactions involve a reaction where a group adds to a molecule.
• Hydrogen is a condition needed for addition of hydrogen to alkenes.
• Steam requires a Ni catalyst, 300 o C and 60atm for addition to alkenes.
• The second step in electrophilic addition is when the carbocation accepts a pair of electrons from the negatively charged ion.
• A major product forms from electrophilic addition because haloalkane is formed in greater amounts because the carbocation is more stable on C-A than on C-B.
• In a reaction, all atoms and bonds shown around the C=C double bond should be shown on the left.
• An electron pair donor is referred to as an elecrophile.
• In a reaction, all atoms and bonds shown around the C-C single bond should be shown on the right.
• One disadvantage of combustion of waste polymers is the formation of toxic waste products, such as HCl, that need to be removed.
• To identify a monomer from an addition polymer, pick 2 C atoms and draw them out with all side attachments and a C=C between them.
• The molecule formed when an alkene reacts with steam is an alcohol.
• The first step in electrophilic addition is when the electrophile accepts a pair of electrons from the pi-bond and the less electronegative atom accepts an electron pair from the electrophile.
• The molecule formed when an alkene reacts with hydrogen bromide is a bromoalkane.
• Addition polymerisation is the type of polymerisation involving alkenes.
• Organic feedstocks are used for the production of plastics and other organic chemicals.
• Hydrogen halides and steam are reagents that can react with asymmetric alkenes to form more than one product.
• The order of stability of carbocations from most to least is tertiary, secondary, primary.
• During electrophilic addition, the H atom has a delta+ charge and accepts an electron pair in H-C l.
• Biodegradable and photodegradable polymers provide environmental benefits.
• A common error students make in drawing the electrophilic addition mechanism is the use of curly arrows pointing in the wrong direction.
• The intermediate in an electrophilic addition is when the C=C has become a C-C bond, one C has a bond to the electrophile, and the other becomes a carbocation.
• Markownikoff's rule is used to predict the major product of electrophilic addition by stating that the H atom of the H-X adds to the C atom with the most H atoms already attached.
• Electrophilic addition is the mechanism that alkenes undergo during addition.