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Chemistry🧪🔫 > 13) ALKENES > Flashcards

13) ALKENES Flashcards

1
Q

how many outer e- does carbon have?

A

4

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2
Q

what does carbon do to achieve a full outer shell?

A

share the 4 e- in 4 covalent bonds

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3
Q

what are the two types of covalent bonds?

A

-sigma
-pi

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4
Q

how is a sigma bond formed?

A

-when carbon only uses 3 of its e- pairs
-each carbon atom has a p-orbital with 1 spare e-

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5
Q

how is a pi bond formed?

A
  • p-orbitals of 2 carbons overlap
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6
Q

where do the 2 orbitals that make up the pi bonds lie on the carbon atoms?

A

lie above + below = maximise bond overlap

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7
Q

what are the bonding arrangement in an alkene?

A
  • 3 sigma bonds
    –> 2 form sigma bonds with other atoms
    –> 1 forms sigma bond with the C of the double bond
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8
Q

describe the shape of an alkene

A

-3 bonding pair e- repel each other
-planar
-120

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9
Q

what is steriomerism?

A

mol. have the same molecular formula + bond arrangement but their atoms are arranged differently

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10
Q

what are the 2 types of steriomerism?

A

1) e/z isomerism
2) cis/trans isomerism

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11
Q

when does cis / trans isomerism occur?

A

when the 2 atoms or group of \toms attached to the C of the C=C bond is the same

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12
Q

when does E/Z isomerism occur?

A

different atoms or group of atoms are attached to each C atom of the C=C bond

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13
Q

describe the position of atoms in saturated compounds?

A

-σ bond atoms are not in fixed position
-free rotation due to
C-C bond

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14
Q

what is a saturated compund?

A

contains single bonds

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15
Q

what is an unsaturated compound?

A

double bonds
C=C

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16
Q

describe the position of atoms in unsaturated compound

A

-groups attached to C=C are fixed in position
-free rotation not possible due to π bond

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17
Q

how can cis isomers be distinguished?

A

two groups on the same side of the double bond

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18
Q

how can trans isomers be distinguished?

A

two groups on opposite sides of the double bond

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19
Q

are alkanes or alkenes more reactive?

A

alkenes are more reactive

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20
Q

why are alkenes more reactive than alkanes?

A

-presence of π bond
-C=C bond requires less energy to break

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21
Q

what are the types of reactions that alkenes can undergo?

A
  • hydrogenation
    -halogenation
    -hydrohalogenation
    -hydration
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22
Q

what is a hydrogenation reaction?

A

reaction between alkene + hydrogen

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23
Q

what catalyst is used in hydrogenation?

A

nickel catalyst

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24
Q

what is the result of a hydrogenation reaction

A

alkane

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25
Q

what is a halogenation reaction?

A

reaction between alkene + halogen

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26
Q

what does a halogenation reaction produce?

A

dihaloalkane

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27
Q

what happens during a halogenation reaction?

A
  • C=C bond broken = new single bond formed
    -halogen bonded to each C
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28
Q

what can halogens be used for?

A

test if a mol. is unsaturated

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29
Q

what colour is bromine water?

A

orange / yellow

30
Q

how can we test if a mol. is unsaturated with bromine water?

A

-unknown compound shaken with bromine water
-addition reaction takes place
-solution decolourises

31
Q

what is a hydrohalogenation reaction?

A

alkene react with hydrogen halides to produce halogenoalkanes

32
Q

what type of reaction is hydrohalogenation?

A

electrophilic addition

33
Q

what happens during a hydration reaction?

A

-alkenes treated with H2SO4 or H3PO4 catalyst
-water added
-converted to alcohol

34
Q

what is the end product of hydration ?

A

alcohol

35
Q

what is electrophilic addition?

A

addition of electrophile to an alkene double bond

36
Q

what is an electrophile?

A

e- pair acceptor

37
Q

why is the the alkene double bond susceptible to attack from electrophiles?

A

area of high e- density

38
Q

is a hydrogen halide mol. polar or nonpolar?

A

polar - difference in electronegativities

39
Q

what happens during an electrophilic addition reaction?

A
  • H atom acts as an electrophile = accepts pair of e- from C=C
    -bond breaks through heterolytic fission
    -C becomes a carbocation (+)
    -δ- atom bonds to carbocation
40
Q

what is a carbocation?

A

positively charged C atom with only 3 covalent bonds

41
Q

what are the 3 types of carbocations?

A

-primary
-secondary
-tertiary

42
Q

what are the alkyl groups attached to the carbocations?

A

-inductive effect
-e- donating groups

43
Q

how is the inductive effect illustrated?

A

arrowheads on bonds

44
Q

what do the bonds with arrowheads show?

A

alkyl groups pushing e- to carbocation

45
Q

what are the effects of the inductive effect?

A

carbocation becomes less +ly charged = charge spread out more = more stable

46
Q

when are the carbocations most stable?

A

tertiary carbocation = have 3 alkyl groups

47
Q

what is a primary carbocation?

A

1 alkyl group attached to carbocation

48
Q

what is a secondary carbocation?

A

2 alkyl groups attached to carbocation

49
Q

what is a tertiary carbocation?

A

3 alkyl groups attached to carbocation

50
Q

which carbocation is the most stable?

A

tertiary

51
Q

which carbocation is the least stable ?

A

primary

52
Q

what is Markovnikov’s rule ?

A
  • in an electrophilic reaction of hydrogen halide to an alkene , the hydrogen will bond to the most substituted C
53
Q

does Markovnikov’s rule favour the major or minor product?

A

major

54
Q

what are the 2 ways an electrophile can attach?

A

1) form major product
2) form minor product

55
Q

where does does the electrophile attach to form the major product?

A

-attach to least substituted C
-most stable

56
Q

where does does the electrophile attach to form the minor product?

A

-attach to most substituted C
-least stable

57
Q

what is addition polymerisation?

A

monomers containing at least 1 C=C forming long chains of polymers

58
Q

what is a polymer?

A

long chain molecule that’s made up of many repeating unit

59
Q

what is a monomer?

A

small reactive mol. that react together to form a polymer

60
Q

what is the general formula of addition polymerisation?

A

W X W X
\ / | |
n C = C –> [ - C – C-]
/ \ | |
Y Z Y Z

61
Q

what is a disadvantage of polymers having low reactivity?

A

makes them non biodegradable

62
Q

what does polymer recycling allow?

A

-reduces the amount of waste going to landfill sites
- reduce the use of finite resources = polymers can be made from crude oil + fractions

63
Q

what is one disadvantage of recycling polymers?

A

-time consuming process to sort into different categories
-need to be chopped, washed, dried + melted = no point if the polymers are mixed

64
Q

why do some polymers have to be destroyed by burning?

A

contain large amount of energy within the polymer chains

65
Q

what is a disadvantage of combusting polymers?

A

-environmental pollution
- C within polymer can be released as CO2 = global warming

66
Q

what is feedstock recycling?

A

waste polymers broken down by chemical + thermal processes into monomers, gases + other oils = used as raw materials for the production of new polymers

67
Q

what is a benefit of feedstock recycling compared to other methods?

A

work with unsorted + unwashed polymers

68
Q

what are bioplastics?

A

polymers made from plant starch / cellulose = provide renewable + sustainable alternatives

69
Q

what are biodegradable polymers?

A

-polymers that can be broken down over time by microorganisms
-broken down using hydrolysis reactions

70
Q

what are compostable polymers?

A

-plant based
-degrade naturally + leave no harmful residue

71
Q

what are photodegradable polymers/

A

-contain bonds that are weakened by absorbing light / visible radiation

72
Q

what are the alternative ways to dispose polymers?

A
  • recycling
    *combustion
  • feedstock recycling
    *bioplastics
    *biodegradable polymers
    *compostable polymers
    *photodegradable polymers

Chemistry🧪🔫 (8 decks)

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