Alkenes + Mechanisms

What is a pi bond

• Direct overlap of p-orbitals above and below

Why are alkenes more reactive than alkanes

• in an alkane the single bond between two carbon atoms is a sigma bond

• in an alkene the double bond between atoms is a pi bond

• the pi bond is weaker than the sigma bond so it takes less energy to break the pi bond

  • sigma bond in alkene remains intact

What is the addition reaction of hydrogen to an alkene and what are the conditions

• alkene + hydrogen → alkane

• unsaturated → saturated

• 150°C, Nickel catalyst, Hydrogen

What is the addition reaction of a halogen to an alkene and what are the conditions

• alkene + halogen → haloalkane

• room temperature, halogen

What does a curly arrow show in a mechanism

• Movement of a pair of electrons to make or break a covalent bond

  • Bond making: arrow points to atom where bond is made to

  • Bond breaking: arrow starts from middle of bond

What is an electrophile

Electron pair acceptor

What is a nucleophile

Atom with lone pair

What is heterolytic fission

• the process where a covalent bond breaks and one atom takes both electrons from the bonded pair

What is electrophillic addition and what are the conditions

• addition of a hydrogen holide to an alkene

• alkene + HX → haloalkane

• room temp

What is Markovnikov’s rule to assign the major product

• the hydrogen atom from HX will bond to the carbon atom in the C=C with the most H atoms already attached directly

What is the explanation of the major product

• the secondary carbocation intermediate produces the major product which is … as it is more stable than the primary carbocation intermediate in …

What is the addition reaction of steam to an alkene and what are the conditions required

• alkene + steam → alcohol

• steam, 300°C, 65atm, H3PO4

How do you draw 1 repeating unit of a polymer

• open the double bond

• add brackets

• add bonds which touch brackets

• n bottom right corner

How do you draw multiple repeating units

• open up all double bonds

• add single bonds on side which do not need brackets

• put number of repeating units

What is the issue with disposing polymers

• non-biodegradable

• combustion releases toxic fumes

How should you dispose polymers safely

• incineration; combustion of polymers to produce energy

• organic feedstock

What is the disadvantage of disposing polymers by incineration and how can this be overcame

• burning polymers with Cl atoms products toxic HCl fumes

• this can be neutralised by using acid scrubbers - alkalis