4B - Alkenes
- Created by: Strelly22
- Created on: 27-03-21 16:18
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- 4B - Alkenes
- definitions
- stereoisomers
- molecules with the same structural formula but a different arrangement of atoms in 3d space
- electrophile
- an atom (or group of atoms) which is attracted to an electron rich centre or atom where it accepts a pair of electrons to form a new covalent bond
- electronegativity
- a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
- stereoisomers
- bonding
- single bond = sigma
- double bond = sigma + pi
- p orbitals overlap sideways above and below the plane of the molecule
- the shorter the bond, the higher the bond enthalpy so stronger the bond
- isomerism
- E/Z isomers
- must have a C=C bond
- must have 2 different groups of atoms attached to each C in the C=C
- CIP Rules
- 1. look at each C in the C=C at a time
- 2. the one with the larger atomic number has higher priority (if same, count next one out)
- 3. Z = the same side. E = opposite sides
- cyclohexene only found in the Z form
- E/Z isomers
- addition reactions
- + H2
- 150
- Ni catalyst
- + halogen
- rtp
- + HBr
- rtp
- + water
- steam
- H3PO4or H2SO4 catalyst
- when alkenes react with halogens or hydrogen, the atoms join to the carbons so only 1 product is formed
- in symmetrical alkenes, 1 product is formed
- in asymmetrical alkenes, 2 isomeric products are formed
- + H2
- Markownikoff's rule
- when an asymmetric alkene reacts with a hydrogen halide or steam, the major product is always formed from the more stable carbocation
- primary = 2 Hs
- secondary = 1H
- tertiary = 0Hs
- 'X is the more stable product because it forms from the more stable (tyertiary/secondary) carbocation
- atom economy and percentage yield
- AE = sum of molar masses of desired products / sum of molar masses of all products x100
- PY = actual yield / theoretical yield x100
- addition polymerisation
- formation of a very long molecular chain by the repeated addition reactions of many unsaturated alkene molecules (monomers)
- see p45 4B to see a diagram
- polymer waste
- methods of polymer disposal
- landfill
- processing
- use as organic feedstock
- use as a fuel
- novel polymers
- bioplastics
- produced from starch, cellulose, plant oils, proteins
- dont require crude oil
- biodegradable
- produced from starch, cellulose
- decompose in landfill + produce no toxic waste
- photodegradable polymers
- oil based polymer. bonds weaken by absorbing light
- decompose rapidly
- bioplastics
- methods of polymer disposal
- definitions
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