3.3.4 Alkenes Flashcards
General Formula of alkenes
CnH2n
What is an alkene?
Unsaturated hydrocarbons with at least one double covalent bond.
Name the reaction that alkenes can undergo
Addition reactions
Property of the double bond that makes them fairly reactive
High electron density
Name of stereoisomerism that occur in alkenes
E-Z Isomersim
Why does this stereoiomersim occur in alkenes?
Restricted roatoation around the C=C double bond, which contain both pi and sigma bonds.
How does the pi bond arrise in alkenes
The overlap of 2p orbitals that occur both above and below the C atoms and prevent free rotation.
What must be present in order for E-Z isomersim to occur
two different groups/atoms attached to both end of the double bond
Name of mechanism that alkenes undergo
Electrophilic addition
Define electrophile
Electron pair acceptor
name 3 electrophiles
-halogen, e.g. Br2
-hydrogen halide, e.g. HBr
-sulfuric acid, H-OSO2OH
name the conditions and reagent for the reaction of bromine with alkenes
room temperature
bromine (Br2)
name the conditions, reagent and functional group formed for hydrogen bromide and alkenes
room temperature
HBr
halogenoalkane
What is ‘Markovnikoff’s Rule’ about the additon of hydogen halides to alkenes?
In most cases, the halogen will be added to the carbon with the fewest hydogen attached to it
What is the positive intermediate called?
Carbocation
Order of carbocation stability
Tertiary>secondary>primary
How do major and minor products arrise
Addition of hydorgen halides to an unsymmetrical alkene
Why is the major product formed
It is formed via the more stable carbocation intermediate
name the conditions, reagent and functional group formed for the reaction between sulfuric acid and alkenes
room temperature
concentrated H2SO4
alkyl hydrogensulfate
name the product formed in the hydrolysis of alkyl hydrogensulfate.
alcohol
what is the overall role of sulfuric acid
catalyst
define hydrolysis
a reaction where the molecule is split by the addition of water.
name the conditions and reagent of the industricla hydration of alkenes to form alcohols
High temperature:300-600°C
High pressure: 70 atm
Concentrated H3PO4 (catalyst)
why is the direct hydration of alkenes preferred in industry
-no waste products
-high atom economy
-easier and cheaper sepeation of products
describe the test for alkenes and the positive result
Bromine water
orange to colourless
name the type of polymers that are formed using alkenes
addition polymers
property of addition polymers
unreactive
properties of poly(chloroethene)
waterproof
electrical insulator
not react with acids
typical uses of poly(chloroethene)
window frame coverings, guttering, electrical wires and waterproof clothing
what do plasticisers do
weaken intermolecular forces in polymer, allowing the chain to move more easily. Results in a more flexible polymer
