C13- Alkenes Flashcards
Stereoisomerism
Molecules with the same structural formula but which occupy different positions in space
Conditions for steroisomerism
Double bonds are present, which cannot freely rotate like single bonds can
Each carbon atom in the double bond has two different groups attached
E/Z isomerism vs optical isomerism
E/Z occurs in compounds with a C=C bond
Optical isomerism happens in compounds with a wider range of functional groups, including alkanes with no functional group
E isomers vs Z isomers
E–> The two largest Groups on opposite sides of the C=C bond
enemies
Z–> The two largest groups are on the same side of the C=C
ze zame zide
Sides are vertical
Cis and trans rules
If one of the attached groups on each side of the C=C is hydrogen
Cis= Z
trans= E
CIP rules
assigns priority of chain substituent groups
The larger the atomic number on the first atom in the substituent group the higher its priority
If these values are equal, continue to the next in the chain
Hydrogenation of alkenes
Opens up C=C bond
Testing for unsaturation of alkenes
Bromine water
When bromine water is added it adds bromine across the double bond, orange colour disappears
Indicates the Prescence of C=C
Pi bond
+ formation
Double bond
Formed due to the perpendicular overlap of P orbitals
One Pi bond forms both above and below the sigma bond
Bromine water
Alkenes
The alkene decolourises bromine water
Removes it by electrophilic addition
Polarised bond
When electrons are unevenly distributed in a chemical bond
Electrophile
An electron deficient species which accept a pair of electrons to form a covalent bond
Carbocation
A chemical species with a positive charge on a carbon atom
Markownikoff’s Rule
carbon cations
Recognises that a more substituted carbon intermediate is more stable and produces the major product
The secondary Carbocation is more stable than the primary
Electrophilic addition
Carbocation formed
Primary, secondary or tertiary carbocation
How to classify Carbocation
Classified by number of alkyl groups on the carbocation
1 other C bonded= primary
2 other C bonded= secondary
Carbocation stability
Addition of a hydrogen halide to an unsymmetrical alkene forms the major product via the most stable carbocation
Primary is least stable, tertiary is most stable
Electrophilic addition
Propene and hydrogen bromide
Mechanism
1 Bromine is mor electronegative than hydrogen, so HBr contains two dipoles
2- the electron pair in the pi bond is attracted to the partially positive hydrogen atom, causing the double bond to break
3- A bond forms between the H atoms of HBr, and a carbon atom that was a part of the double bond
4- Th HBr bond breaks by heterolytic fission, and the electron pair goes to the bromine atom
5- Bromide ion and Carbocation formed
6- Bromide ion reacts with carbocation to form the addition product
Hydration of alkenes
Produces alcohols
steam adds across the double bond
Hydration of alkenes
conditions
Steam
acid catalyst (phosphoric acid)
Alkenes polymerisation
Addition polymerisation
rules for drawing repeat units
written in square brackets
after the bracket place the letter ‘n’ to show there is a large number of repeats
What is a repeating unit
specific arrangement of atoms in a polymer that repeat over and over again
Polyethene and polychlorotethene uses
polyethene- supermarket bags, straws, toys
PVC- flexible or rigid- pipes, bottles flooring
Disposing of waste polymers
challenges
lack of reactivity presents chemists with a challenge
they’re non biodegradable
Recycling of polymers
2 adv 1dis
conserves finite fossil fuels
decreases waste gone to landfill
discarded polymers have to be sorted by type
PVC recycling
hazardous due to high contents of chlorine
New technology can dissolve the polymer and recover it by precipitation
Waste polymers used for fuels
Can be incinerated to produce heat
Feedstock recyling
chemical and thermal processes that reclaim monomers gases or oils from the waste
products resemble those from crude oil in refineries
Can handle unsorted and unwashed products
Bioplastics
Produced from plant starch
Biodegradable polymers
Can be broken down by microorganisms into water CO2 and biological components
compostable polymers degrade and leave no visible or toxic residues
Photodegradable polymers
Photodegradive oil based polymers
contain bonds that are weakened by light
Toxic gas produced upon combustion of PVC
HCl
Unsaturated hydrocarbon
definition
An unsaturated compound contains double or triple covalent bonds.
A hydrocarbon is a compound of carbon and hydrogen only
electrophile
An atom or group of atoms that accepts a pair of electrons to form a new covalent bond
nucleophile
An atom or group of atoms that donates a pair of electrons to form a new covalent bond
Catalyst needed for an alkene to react with hydrogen
nickel
Catalyst need for an alkene to react with steam
steam in the presence of an acid catalyst
3 ways in which waste polypropene polymers can be processed in a sustainable way
recycling
combustion for energy production
use as an organic feedstock
Naming molecules with multiple prefixes
alphabetical
e. g 2 chloro 3 methyl
Why are biodegradable polymers, made form plants unlikely to be carbon netural
while plants take in and release equla volumes of co2
manufacturing and harvesting crop will use fossil fuels, releasing co2
CIP explain exam technique
specify the atoms and which has higher atomic number
