properties of alkene Flashcards
Why do double bonds make alkenes reactive
sigma have a high electron density
Pi bond has a relatively low bond enthalpy
Easy to break, more reactive
What is different about cycloalkenes
Have 2 fewer hydrogens
What do double bonds contain
Pi bond and sigma bonds
When do sigma bonds happen
When 2 s orbitals overlap.
They align horizontally to give a single covalent bond
Sigma bond properties
Strong electrostatic force of attraction between nuclei and shared pairs of electrons due to high electron density between nuclei
Has a high bond enthalpy
What are pi bonds
Parallel overlap of 2 p orbitals above and below the bonding c atoms
Why are pi bonds weaker than sigma bonds
Electron density is spread out above and below the nuclei. The electrostatic attraction is weaker so they have a weaker bond enthaply making them more reactive
Why are alkanes less reactive
Only have sigma bonds
They are non polar
What are alkenes good for
Polymers and petrochemicals
Why are alkenes open to attack from electrophiles
Pi bond sticks out a little and the whole double bond has a high electron density
Electrophile adds to the molecule
What does stereoisomerism occur on
Alkenes
contain double bond
Atoms cant rotate around the double c bond and is rigid
Stereoisomers meaning
Same structural formula but the different arrangement in atoms
What are electrophiles
Electron pair acceptor
Deficient in electrons
Example of electrophiles
delta positive polar bonds, positive ions
Test for alkenes
Bromine water - orange to colorless
electrophilic addition hydrogen gas with ethene conditions
150 degrees, nickel catalyst,
make ethane
What does the hydration of alkenes make
alcohol
hydration of alkene conditions
steam and acid catalyst
What do alkenes reacted with hydrogen halides make
halogenoalkanes
Landfill is useful for disposing plastics that
- are too difficult to recycle
- Too difficult to separate from other materials
- Not enough plastic to extract it
Why is it hard to dispose of polymers
Not biodegradable
what recycled plastic can be used for
plastics cracked into monomers and used as an organic feedstock for plastic or other substances
Some plastics can be remoulded
When is incineration used to dispose of plastic
plastic cant be recycled
energy from burning used to generate energy
Why is burning plastic bad
Can release toxic fumes
Chlorine-based plastics produce harmful HCL gas when burned.
Flue gas scrubbers used to neutralise acidic gases by firing a base
what does biodegradable polymers need to biodegrade
good supply of oxygen and moisture
Light and water so microorganisms can digest
what are biodegradable polymers made from
oil fractions and renewable sources
More expensive than non-biodegrable plastics
Benfit to environment of biodegradable polymers
Less land use, decompose
Can be made from renewable materials reducing dependency in crude oil
What is needed to break down photodegrable polymers
Light
Why does bromine water go orange to colourless in presence of alkenes
Will undergo an electrophilic addition reaction due to the double c bond
Shape of alkenes
trigonal planar
Why the shape of an alkene trigonal planar
3 regions of electron density around each carbon atom
Electrons repel each other
All of the atoms are in the same plane
Why are alkenes so rigid
Position of the pi bonds electron density above and below the plane of the sigma bond
When do cis-trans isomers occur
One of the attached group on each carbon atom on the double bond must be hydrogen.
What is carbocation
Positively charged carbon atom
Why is tertiary carbocation the most stable
The more alkyl group attached to the positively charged carbon atom the more the charge is spread out making the ion more stable
