3.3.4 Alkenes

Question 1

what are alkenes

Answer 1

unsaturated hydrocarbons

Question 2

what type of bonding do alkenes have

Answer 2

a double covalent bond

Question 3

what is the area of the double covalent bond refered to

Answer 3

a centre of high electron density

Question 4

what is the general formula for alkenes

Answer 4

CnH2n

Question 5

is there rotation in the carbon double bond if alkenes

Answer 5

no

Question 6

what is used for the test of alkenes

Answer 6

bromine water

Question 7

what is the positive result for the presence of an alkene

Answer 7

orange to colourless

Question 8

what is a molecule with a positive charge called

Answer 8

cation

Question 9

explain why there is an attraction between a C=C double bond and Br2.
(3 marks)

Answer 9

• the sigma bond between the C=C bonds is an area of high electron density.
• the Br2 becomes polariseed
• the delta positive Br iis attracted to the C=C bond

Question 10

why is there a colour change between thee bromine water and an alkene

Answer 10

cause the Br2 is an electrophilie which is attracted to the areas of high electron density.

Question 11

what reactions do alkenes undergo

Answer 11

electrophilic addition

Question 12

what is the name of the mechanism where the double bond is eliminated

Answer 12

electrophilic addition

Question 13

what are the elements that undergo electrophilic addition with alkenes

Answer 13

HBr
H2SO4
Br2

Question 14

what is the first stage of electrophilic addition

Answer 14

• the double bond attacks the delta positive element

Question 15

what is the 2nd stage of electrophilic addition

Answer 15

the bond breaks between the 2 elements.

[so the arrow is from the bond to the element]

Question 16

what happens after the 2nd stage of electrophilic addition

Answer 16

the delta positive joins the alkene
where the pi bond is broken already
and theres aleady sigma bonds

Question 17

what happens in the 3rd stage of electrophilic addition

Answer 17

the delta negative element with lone pairs and a negative charge creates a bond with the carbocation

Question 18

what forms after the delta positive binds to the new molecule

Answer 18

a carbocation

Question 19

what shouldnt you forget for the carbo cation

Answer 19

the plus
by the lonley carbon

Question 20

what type of forces do alkenes have

Answer 20

van Deer Waal forrces

Question 21

what is attracted to the high electron density region of the double bond

Answer 21

an electrophile

Question 22

what is an electrophile (1 mark)

Answer 22

electron pair acceptor

Question 23

what happens to the molecules when they come in contact with the alkene

Answer 23

an induced dipole

Question 24

kinda describe the structure of sulphuric acid

Answer 24

s in the middle
with two double bonds on either side
each double bond is attached to an oxygen
up and below the s is OH binded.
the O binds with the S

Question 25

what forms from unsymmetrical alkenes

Answer 25

a major and minor product

Question 26

what are the major products

Answer 26

carbocations that are bonded to more alkyl groups

Question 27

what are primary carbocations

Answer 27

bondedd to 1 alkyl group

Question 28

what are secondary carbocations

Answer 28

bonded to 2 alkyl groups

Question 29

what are tertiary carbocations

Answer 29

bonded to 3 alkyl group

Question 30

what is the role of thee alkyl groups

Answer 30

the donate electron density which stabilises the carbocation they have a positive inductive effect

Question 31

what is the most stable carbocation? And why is this

Answer 31

a tertiary carbocation it has more alkyl groups which have more positive inductive effects

Question 32

(b) State what you would observe if bromine water was added to poly(chloroethene). Explain this observation.

Answer 32

no colour change the polymer is saturated and does not contain any double bonds

Question 33

explain why more of isomer E than isomer F is formed in this reaction. (2 marks)

Answer 33

isomer E is the major product as its formedd from a more stable secondary carbon cation. secondary carbocations are more stable than primary carbocations

Question 34

how are addition poylmers formed

Answer 34

from alkenes and subsitiuted alkenes

Question 35

what is PVC known as?

Answer 35

poly(chloeothene)

Question 36

why are addition polymers unreactive

Answer 36

the carbon-carbon single bonds aree strong and polar

Question 37

what are properties of addition polymers

Answer 37

they are rigid and strong

Question 38

why do addition polymers have high melting and boiling points

Answer 38

due to an increase in van-Deer Waal forces cause there are more electrons in the long chain

Question 39

what hydrocarbon is more stable

Answer 39

a saturated hydrocarbon

Question 40

what are the forces present in poly(chloroethene)

Answer 40

permanenet dipole dipole forces van-Deer waal forces

Question 41

how can we modify PVC

Answer 41

using plasticiers

Question 42

what do plasticisers do to PVC

Answer 42

it makes it flexible

Question 43

how do plasticsiers work

Answer 43

they reduce the intermolecular forces between C and Cl