Alkenes

Question 1

What is an alkene
What is the General Formula

Answer 1

Unsaturated hydrocarbons with a C=C Bond
C(n) H(2n)

Question 2

Why is there no rotation about the C=C double bond

Answer 2

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

Question 3

Explain the reactivity of an alkene compare to that of a alkane

Answer 3

Alkenes are more reactive then alkanes due to high electron density of the double bond accepting electrophiles readily.

Question 4

What intermolecular forces does an alkene have?

Answer 4

VDW only
(Not polar so no permanent dipole & doesnt form H-O, H-F, H-N so no Hydrogen bonding either)

Question 5

Explain a hydrocarbons solubility?

Answer 5

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

Question 6

What kind of isomers can alkenes get?

Answer 6

Structural: Chain (branched chains), Position(c=c on different bonds), Geometric (E & Z Isomers)

Question 7

What is an Electrophile?

Answer 7

Lone pair Acceptors

Question 8

Why is a tertiary carbocation the most stable?

Answer 8

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

Question 9

Major products are _________________

Answer 9

The products which are most stable

Ie. Tertiary or secondary products

Question 10

What conditions are needed for the electrophilic addition of H2O to an alkene.
What is Produced?

Answer 10

Acid Catalyst usually H3PO4
300 Degrees, 60-70 ATM
An Alcohol

Question 11

Draw the mechanism for the addition of water to ethene

Answer 11

Question 12

What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?

Answer 12

20 Degrees , HX

Question 13

Draw the Mechanism for the reaction of HBr and ethene

Answer 13

Question 14

How does a molecule with C=C react with an electrophile?

Answer 14

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

Question 15

Draw the mechanism foe the reaction between bromine and ethene

Answer 15

Question 16

Draw the mechanism for the reaction of sulphuric acid with ethene

Answer 16

Question 17

What is an Addition Polymer?

Answer 17

Formation of long chain molecules from lost of small molecules (monomers) with no other products

Question 18

What are Monomers?

What functional group do they commonly have?

Answer 18

Small molecules which each stand as a repeating unit of a polymer

Usually have a C=C which breaks when polymerisation takes places

Question 19

Draw the polymerisation of ethene?

Answer 19

Question 20

Give 3 uses of Poly(chloroethene)

Answer 20

Aka Pvc:

Drainage pipes (without plasticiser)
Vinyl and
Aprons (with plasticiser)

Question 21

What is a Plasticiser?
Give Examples

Answer 21

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

Question 22

Why do molecules with C-C and C-H dont decompose easily.
What problems arises because of this?

Answer 22

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

Question 23

What is Mechanical recycling?

Answer 23

Where plastics are separated into different types washed; ground down ;melted and remoulded.

Question 24

What is Feedstock recycling
What is it used for?
Why is reusing previously feedstocked plastics problematic?

Answer 24

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.

Question 25

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.

Answer 25

Goes from Cloudy ——> Clear