4.1.3 - Alkenes Flashcards
Alkenes general formula and saturation
- CnH2n
- Unsaturated
Blurt everything you know about sigma bonds σ
- overlap of
orbitals directly between the bonding atoms. - σ bond has direct overlap of orbitals.
- σ bond has electron density between bonding atoms
- Stronger than pi bonds
- Present in single, double and triple bonds
- Free rotation around bond axis
Blurt everything you know about pi bonds π
- side way overlap of two p orbitals
- π bond is above
and below the bonding atoms - π bond has sideways overlap
- π bond is weaker than a σ bond (has low bond enpalthy).
- π bond has electron density above and below bonding atoms
- Present in double and triple bonds only
- Restricted rotation
shape around the each carbon in C=C bond
Trigonal planar
120 degrees
Label where the sigma and pi bond is in a C=C bond
Reactivity of alkenes
Things to remeber when doing E Z isomerism
- Carbons with the same groups attached can be E Z isomers e.g H, CH3, Cl attached to each carbon in the double bond
- Z is Zame side - cis
- E - Enemy (opposite side) - trans (transgender switching to the opposite gender)
- Priority is given to the group with the higher atomic number
What is an electrophile
Electron pair acceptor
What is an nucleophile
Electron pair donor
Blurt everything you know about alkenes to alkanes including the reagents, and an example: ethene goes to ?
Reagent: hydrogen
Conditions: nickel catalyst
Type of reaction: Addition/reduction/hydrogeation
temperature of about 150°C
Blurt everything you know about alkenes to dihaloalkane including the reagents, and an example: ethene goes to ?
Reagent: Bromine
Conditions: Room temperature
Mechanism: Electrophilic Addition
Type of reagent: Electrophile, Br+ Type of Bond Fission: Heterolytic
Blurt everything you know about alkenes to haloalkanes including the reagents, and an example: but-2-ene to 2- goes to ?
Reagent: HCl or HBr (hydrogen halide)
Conditions: Room temperature
Mechanism: Electrophilic Addition
Type of reagent: Electrophile, H+
what is Markownikoff’s rule ?
In most cases, the halogen in the halogen carrier(HCL or HBr) will be added to the carbon with the fewest hydrogens attached to it
What is the order of stability for carbocations
- tertiary > secondary >primary
- In electrophilic addition to alkenes, the major product is formed via the more stable carbocation intermediate.
Blurt everything you know about alkenes to alcohols including the reagents, and an example : ethene to ethanol
-
Reagent : steam
Essential Conditions - High temperature 300 to 600°C
- High pressure 70 atm
- Catalyst of concentrated H3PO4
- This reaction can be called hydration: a reaction where water is added to a molecule
Blurt everything you know about alkenes to poly(alkene) including the reagents, and an example :polyethene
- high pressure
- Catalyst
- addition polymerization reaction
- Easiest way to do it is to make the chain look like a E/Z isomer first then remove the double bonds and put it in brackets
- Or put the number of how many repeating units they want or ‘n’ if its unspecified outside right next to the brackets
Benefits of using waste polymers
- Combustion for energy production
- Organic feedstock
- removal of toxic waste products, e.g.
removal of HCl formed during disposal by
combustion of halogenated plastics
(e.g. PVC)
what does the picture show
what are some disadvantages of poly(alkenes)
Non-biodegredable
the benefits to the environment of development
of biodegradable and photodegradable polymers.
- There will be a reduced dependency on finite
resources (crude oil) and alleviating problems from disposal of persistent plastic waste - Reduced CO2 emissions
- Less accumulation of plastic waste in landfills, oceans, and natural environments.
What type of reactions do alkenes undergo
Electrophilic addition
( as an electrophile - a electron pair acceptor - has been added)
Why can sigma bonds freely rotate whereas pi bonds can’t ?
When can we use e/Z and cist trans
