Alkenes Flashcards
What is a Stereoisomerism?
Molecules with the same molecular and structural formula but a different array in space.
What is an E isomer
• Two higher priority groups are attatched to the carbon on OPPOSITE sides of the double bond.
What is a Z isomer
• Two higher priority groups are attatched to the carbon on the SAME side of the double bond.
What property should each carbon on the double bond have
• Be bonded to 2 different atoms or groups
• two identical groups cant be joined to the same carbon
Which atom takes priority?
atom attached to the carbon with the higher atomic number.
What is an Electrophile?
An electron pair acceptor
Electrophiles that react with alkanes have..
an atom with a partially positive charge
What causes the carbon double bond to break?
When a pair of electrons from the double bind are donated to the electrophile.
What happens when the C=C bond in an alkene breaks?
Alkenes undergo addition reactions and form a single bond.
What happens in electrophilic addition?
• pair of electrons from the C=C bond form a covalent bond with delta positive X atom
• X-Y bond breaks forming :Y- ion
• lone pair on :Y- form covalent bond with +ve carbon
How are alkyl hydrogensulphates formed?
Alkenes are absorbed by cold, concentrated sulfuric acid (H2SO4) which is an electrophille
What happened when you add hydrogensulfate to water?
Causes hydrolysis and ethanol is produced.
Adding HBR/H2SO4 to an unsymmetrical alkene forms..
a major and minor product.
What is a major product?
Product formed from the most stable carbocation.
What is the equation for Direct Hydration?
ethene + water—————> ethanol
(conc. H2SO4)
What role does sulfuric acid have in direct rehydration?
Catalyst
What is a Primary (1°) Carbocation?
1 carbon is bonded to the positively charged carbon atom.
What is a Secondary (2°) Carbocation?
2 carbons bonded to the positively charged carbon atom.
What is a Tertiary (3°) Carbocation?
3 carbons bonded to the positively charged carbon atom.
What is the electron releasing property of an alkyl group called?
Positive inductive effect ( electron pushing )
Number of alkyl groups around positively charged carbon increases with..
stability of carbocation
What forms a minor product?
The less stable carbocation
What is a polymerisation recation?
Reaction that joins together many small molecules(alkenes) to form a very large molecule (polymer).
They form a polyalkene which are unreactive.
How are polyalkekes represented?
Using a repeating unit.
Describe poly(chloroethene)
• hard and rigid
• due to permanent dipole-dipole forces between chains.
• this is due to delta positive C and delta negative Cl
How are Plasticisers used?
• added to poly(chloroethene) to reduce effectiveness of the attractions
• this makes plastic more flexible
Why cant plastics be broken down?
• non biodegradable due to strong covalent non polar bonds between atoms in polymer molecules
Why dies plastic take do long to decompose?
It cant be broken down by nucleophiles.
How can polymers be remoulded?
by heating the polymer
• this breaks the weak van der waals forces between polymer molecules