Alkenes Summary
- Created by: Beckaboo
- Created on: 01-05-20 10:05
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- Alkenes
- Properties
- General formula = CnH2n
- Unsaturated
- Has a double bond
- One s-bond and one p-bond
- 120* angles around C=C bond
- equal repulsion
- 3 bonding regions
- Insoluble in water
- Alkenes are non-polar; water is polar
- Like dissolves like
- Alkenes are non-polar; water is polar
- Boiling point increases with chain length
- More points of contact
- More induced dipole dipole interactions
- Lower boiling point than corresponding alkane
- They don't pack as well
- Lower Mr so less induces dipole dipole interactions
- Stereoisomers
- Same structural formula with different spatial arrangement
- p-bond restricts rotation
- Requires a C=C double bond
- Each carbon must be bonded to different atoms or groups
- E = opposite side
- If two of the substituent groups are the same, it is also a trans-isomer
- Z = same side
- If two of the substituent groups are the same, it is also a cis-isomer
- CIP Rules
- Based on atomic numbers
- Highest takes priority
- If highest are diagonally opposite it is an E-isomer
- If highest are on the same side of the C=C bond, it is a Z-isomer
- If they are equal, look at adjacent atoms
- Longer alkyl chains take priority
- Based on atomic numbers
- Reactivity
- More reactive than alkanes
- p-bond has a lower bond enthalpy than s-bond
- p-bond positioning makes it easier to "attack" the electrons
- Addition reactions
- 2 reactants form a single product
- Types of reaction
- Hydrogenation
- + hydrogen
- = alkane
- Bromination
- + bromine
- Mix at RTP
- = dibromo-alkane
- With Hydrogen Halides
- + HBr/HCl
- Mix at RTP
- = bromoalkane
- Hydration
- + water (g)
- 300*, 6MPa, H3PO4 catalyst
- = alcohol
- Hydrogenation
- More reactive than alkanes
- Electrophylic Addition
- Electrophile
- an electron pair acceptor, often positive ions
- Heterolytic fission
- splitting of a covalent bond where one atom takes both electrons
- Diagrams must show
- Curly arrows
- Half arrow head = one electron
- Full arrow head = two electrons
- Lone pairs
- Curly arrows
- Markovnikov's Rule
- Asymmetrical alkene + hydrogen halide
- H will bond to the C with the most H present
- Carbonium ions are more stable when bonded to more alkyl groups
- Inductive effect
- A tertiary carbonium ion is the most stable
- Electrophile
- Polymers
- Addition polymerisation
- Each individual repeating unit is called a monomer
- Most are not biodegradable
- Hard to dispose of
- Properties
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