ALKENES

Question 1

Define alkene

Answer 1

An unsaturated hydrocarbon

With a C=C functional group

Question 2

What is the general formula for alkenes

Answer 2

CnH2n

Question 3

Outline the bond angles around the C=C in an alkene

Answer 3

120C

Question 4

Outline the type of bonding in the C=C bond of an alkene

Answer 4

One sigma bond and one pi bond

Making them vulnerable to attack from electrophiles

Question 5

Define elctrophile

Answer 5

Electron pair acceptor

Question 6

Outline a pi bond

Answer 6

Sideways overlap of p orbital

Contains to pi bonds

Very reactive
Due to lower bond enthalpy

Question 7

Define addition reaction

Answer 7

A reaction where two molecules react together to produce one

Question 8

Outline the reaction of bromine with alkenes

Answer 8

Reagent: bromine
electrophiles Br (partial pos.)
Conditions: room temp no uv light
Mechanism: Electrophilic addition

Alkene to dihalogenalkane

Question 9

Outline an Electrophilic addition mechanism

Answer 9

C=C bond breaks to the induced dipole of Br2

Br2 bond breaks to the (delta negative Br)

Bromide ions lone pair attack the carbocation

Question 10

Outline the reaction of Hydrogen Bromide with Alkenes

Answer 10

Reagent: HCl or HBr
Electrophile H (delta pos.)
Conditions: room temperature
Mechanism: Electrophilic addition

Alkene to halogenoalkane

Question 11

Define markownikoff’s rule

Answer 11

In most cases the bromine will be added to the carbon with the fewest hydrogens attached to it

Question 12

In _____ addition to alkenes the _____ product is formed via the ____ stable _____________ intermediate

Answer 12

Electrophilic
Major
More
Carbocation

Question 13

Outline the stability of a carbocation

Answer 13

(most stable) tertiary, secondary, primary (least stable)

More carbon atoms surrounding carbocation on tertiary than primary
More electron realising reducing the ion charge and stabilising it

Question 14

Which carbocation will form the majority product

Answer 14

(most) tertiary, secondary, primary (least)

Question 15

Outline the reaction of sulphuric acid with alkenes (Stage 1)

Answer 15

Reagent: concentrated H2SO4
Electrophile, H2SO4
Conditions: Room temperature
Mechanism: Electrophilic addition

Alkene to alkyl hydrogensulphate

Question 16

Outline the structure of H2SO4

Answer 16

H-O    O
       \  //
        S
       /  \\
H-O    O

H-OSO2OH

Question 17

Outline the reaction of sulphuric acid with alkenes (Stage 2)

Answer 17

Reagents: Water
Conditions: Warm mixture
Mechanism; None (hydrolysis)

Alkyl hydrogensulphate to alcohol

Question 18

Define hydrolysis

Answer 18

A reaction where the molecule is split by the addition of water

Question 19

How can alkenes be industrially hydrated to alcohols

Answer 19

React with water in the presence of a catalyst

CH2=CH2 + H20 > CH3CH2OH

Question 20

Define hydration

Answer 20

A reaction where water is added to a molecule

Question 21

What are conditions for alkenes to be industrially hydrated to alcohols

Answer 21

High temperatures (300-600C)
High pressure (70atm)
Catalyst of concentrated H3PO4

Question 22

Outline the test for alkenes

Answer 22

Bromine Water (Br2 aq)
Orange to colourless

Tests for the presence of a double bond

Question 23

Define addition polymer

Answer 23

Formed from alkene monomers into a long polyalkene chain

Question 24

Outline the uses of poly(chloroethene)

Answer 24

Water proof, electrical insulator, doesnt react with acids

Rigid platic (strong intermolecular bonding)

uPVC window frames and guttering (pure)

PVC for wire insulation and waterproof clothing (when plasticiser is added)