Alkenes Flashcards
What is an alkene
What is the General Formula
Unsaturated hydrocarbons with a C=C Bond
C(n) H(2n)
Why is there no rotation about the C=C double bond
Due to the Pi Orbital - overlapping pi clouds of electron density above and below the double bond hold the atom in place and don’t allow for rotation
Explain the reactivity of an alkene compare to that of a alkane
Alkenes are more reactive then alkanes due to high electron density of the double bond accepting electrophiles readily.
What intermolecular forces does an alkene have?
VDW only
(Not polar so no permanent dipole & doesnt form H-O, H-F, H-N so no Hydrogen bonding either)
Explain a hydrocarbons solubility?
Not soluble in water
C and H have similar electronegativities and symmetrical structure which results in a non polar molecule
Non polar molecules are not soluble in a polar solvent like water
What kind of isomers can alkenes get?
Structural: Chain (branched chains), Position(c=c on different bonds), Geometric (E & Z Isomers)
What is an Electrophile?
Lone pair Acceptors
Why is a tertiary carbocation the most stable?
Alkyl groups cause a positive inductive effect which increases stability by pushing electrons towards the central carbon
Therefore a tertiary carbocation is the most stable due to having the most alkyl groups
Major products are _________________
The products which are most stable
Ie. Tertiary or secondary products
What conditions are needed for the electrophilic addition of H2O to an alkene.
What is Produced?
Acid Catalyst usually H3PO4
300 Degrees, 60-70 ATM
An Alcohol
Draw the mechanism for the addition of water to ethene
What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?
20 Degrees , HX
Draw the Mechanism for the reaction of HBr and ethene
How does a molecule with C=C react with an electrophile?
C=C double bond with a high electron density induces a temporary dipole in the halogen molecule
The electrons within the pi bond are then attracted to the delta positive dipole on the molecule
Draw the mechanism foe the reaction between bromine and ethene
Draw the mechanism for the reaction of sulphuric acid with ethene
What is an Addition Polymer?
Formation of long chain molecules from lost of small molecules (monomers) with no other products
What are Monomers?
What functional group do they commonly have?
Small molecules which each stand as a repeating unit of a polymer
Usually have a C=C which breaks when polymerisation takes places
Draw the polymerisation of ethene?
Give 3 uses of Poly(chloroethene)
Aka Pvc:
Drainage pipes (without plasticiser)
Vinyl and
Aprons (with plasticiser)
What is a Plasticiser?
Give Examples
Small molecules which get in-between polymer chains and allows them to slide more easily over each other and adds to the flexibility of the material.
Esters and phthalates
Why do molecules with C-C and C-H dont decompose easily.
What problems arises because of this?
Bonds are non polar which are not reacted easily or biodegradable by enzymes
Disposal is probamatic, most end up in land fill
Cannot decompose in water sources ie oceans or lakes
What is Mechanical recycling?
Where plastics are separated into different types washed; ground down ;melted and remoulded.
What is Feedstock recycling
What is it used for?
Why is reusing previously feedstocked plastics problematic?
Plastics heated to a temperature which break polymer bonds leaving original monomers that can be made into new plastics
The creation of entirely new plastics
Each time Thermosoftening plastics are melted and remoulded their physical properties degrade.
So they can only be remoulded a limited number of time.
Cyclohexanol is Converted to cyclohexane within a distillation set up
He then Add Anhydrous calcium chloride to the solution.
How can he tell if the cyclohexene is rid of its water contaminants.
Goes from Cloudy ——> Clear
