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chemistry A1 organic > 3.3.4 Alkenes > Flashcards

3.3.4 Alkenes Flashcards

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1
Q

what are alkenes

A

unsaturated hydrocarbons

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2
Q

what type of bonding do alkenes have

A

a double covalent bond

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3
Q

what is the area of the double covalent bond refered to

A

a centre of high electron density

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4
Q

what is the general formula for alkenes

A

CnH2n

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5
Q

is there rotation in the carbon double bond if alkenes

A

no

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6
Q

what is used for the test of alkenes

A

bromine water

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7
Q

what is the positive result for the presence of an alkene

A

orange to colourless

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8
Q

what is a molecule with a positive charge called

A

cation

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9
Q

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

A
  • 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
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10
Q

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

A

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

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11
Q

what reactions do alkenes undergo

A

electrophilic addition

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12
Q

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

A

electrophilic addition

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13
Q

what are the elements that undergo electrophilic addition with alkenes

A

HBr
H2SO4
Br2

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14
Q

what is the first stage of electrophilic addition

A
  • the double bond attacks the delta positive element
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15
Q

what is the 2nd stage of electrophilic addition

A

the bond breaks between the 2 elements.

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

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16
Q

what happens after the 2nd stage of electrophilic addition

A

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

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17
Q

what happens in the 3rd stage of electrophilic addition

A

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

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18
Q

what forms after the delta positive binds to the new molecule

A

a carbocation

19
Q

what shouldnt you forget for the carbo cation

A

the plus
by the lonley carbon

20
Q

what type of forces do alkenes have

A

van Deer Waal forrces

21
Q

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

A

an electrophile

22
Q

what is an electrophile (1 mark)

A

electron pair acceptor

23
Q

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

A

an induced dipole

24
Q

kinda describe the structure of sulphuric acid

A

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

25
Q

what forms from unsymmetrical alkenes

A

a major and minor product

26
Q

what are the major products

A

carbocations that are bonded to more alkyl groups

27
Q

what are primary carbocations

A

bondedd to 1 alkyl group

28
Q

what are secondary carbocations

A

bonded to 2 alkyl groups

29
Q

what are tertiary carbocations

A

bonded to 3 alkyl group

30
Q

what is the role of thee alkyl groups

A

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

31
Q

what is the most stable carbocation? And why is this

A

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

32
Q

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

A

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

33
Q

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

A

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

34
Q

how are addition poylmers formed

A

from alkenes and subsitiuted alkenes

35
Q

what is PVC known as?

A

poly(chloeothene)

36
Q

why are addition polymers unreactive

A

the carbon-carbon single bonds aree strong and polar

37
Q

what are properties of addition polymers

A

they are rigid and strong

38
Q

why do addition polymers have high melting and boiling points

A

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

39
Q

what hydrocarbon is more stable

A

a saturated hydrocarbon

40
Q

what are the forces present in poly(chloroethene)

A

permanenet dipole dipole forces
van-Deer waal forces

41
Q

how can we modify PVC

A

using plasticiers

42
Q

what do plasticisers do to PVC

A

it makes it flexible

43
Q

how do plasticsiers work

A

they reduce the intermolecular forces between C and Cl

44
Q
A

chemistry A1 organic (5 decks)

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