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AL. OCR Chemistry > organic chem - alkanes and alkenes > Flashcards

organic chem - alkanes and alkenes Flashcards

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1
Q

3 steps of bromination

A
  • initiation
  • propagation
  • termination
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2
Q

explain first step of bromination

A
  • initiation - UV light sets off reaction by splitting apart the Br2 molecules, creating 2 Br radicals
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3
Q

explain third step of bromination

A
  • termination - 2 radicals come together and give pairing of electrons, becoming stable
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4
Q

disadvantages of bromination by a means of producing bromoalkanes

A
  • cant control products made

- cant control isomers made

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5
Q

explain second step of bromination

A
  • propagation - chain reactions - Br radical reacts with C-H bond in methane, forming methyl radical and HBr
  • methyl radical reacts with Br2 making bromomethane and Br radical
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6
Q

unbranched alkane molecules get bigger - bp?

A

increase - as attraction increase (London forces increase)

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7
Q

branched alkane molecules get bigger - bp?

A

decrease - as branches mean molecules cant get close to each other - attraction is less, intermolecular forces are weaker (London forces decrease)

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8
Q

Z isomer

A

same side of double bond

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9
Q

E isomer

A

different side of double bond

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10
Q

sis isomer

A

same side of double bond

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11
Q

trans isomer

A

different side of double bond

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12
Q

when do you use sis-trans isomerism?

A

if other group on the carbon is a hydrogen

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13
Q

stereoisomer

A

atoms in the isomer are in the same order but have different arrangements in space

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14
Q

how do E/Z and cis/trans isomers arise?

A

restricted movement around C=C bond

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15
Q

when there are different elements around the c=c, which do you take?

A

highest priority from each side (highest atomic number)

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16
Q

ester functional group

A

-COOC

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17
Q

aldehyde functional group

A

-CHO

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18
Q

ketone functional group

A

C(CO)C

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19
Q

aliphatic

A

carbons joined In unbranched, straight chains OR branched chains OR non-aromatic rings

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20
Q

aromatic

A

some or all of carbons found in a benzene ring

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21
Q

alicyclic

A

carbon atoms joined in a ring (cyclic structures with/without branching)

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22
Q

alkynes

A

at least 1 C=C bond

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23
Q

amino functional group

A

NH3

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24
Q

nitrile functional group

A

CN (triple bond)

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25
Q

empirical formula

A

simplest ratio of the atoms of each element in a compound

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26
Q

molecular formula

A

number and type of atoms in each compound

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27
Q

general formula

A

simplest algebraic formula for the homologous series (eg. CnH2n)

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28
Q

displayed formula

A

shows relative positions of atoms in a molecule and the bonds between them

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29
Q

structural formula

A

shows arrangement of atoms in a molecule

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30
Q

skeletal formula

A

simplified organic formula - removing all C and H atoms and bonds to H atoms

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31
Q

homolytic fission

A

bond breaks and each atom takes 1 of the electrons from the shared pair

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32
Q

ways of breaking a covalent bond

A
  • homolytic fission

- heterolytic fission

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33
Q

heterolytic fission

A

bond breaks and one of the atoms take both electrons from the shared pair

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34
Q

conditions for reaction of alkanes and halogens

A

sunlight - uv radiations provides activation energy

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35
Q

why are alkenes more reactive then alkanes

A

C=C allows addition reactions to take place much more easily as π bond breaks more easily then σ bond (only bond in alkanes)

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36
Q

bonds in alkenes

A

σ and π

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37
Q

reaction of alkene -> alkane

A

HYDROGENATION

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38
Q

conditions for hydrogenation

A

423K, nickel catalyst - alkene reacted with hydrogen

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39
Q

reaction of alkene -> haloalkane (eq. + conditions)

A

alkene + gaseous hydrogen halide –(room temp)–> haloalkane

40
Q

reaction of alkene -> alcohol

A

HYDRATION

41
Q

conditions for hydration

A

alkene + steam –> alcohol

phosphoric acid catalyst

42
Q

products of oxidisation of primary alcohols

A

aldehydes -> carboxylic acids

43
Q

products of oxidisation of secondary alcohols

A

ketones

44
Q

why are alcohols soluble

A

polar molecules due to difference in electronegativity between O and H

45
Q

boiling point trend down group of haloalkanes

A

increase - as van Der Waals forces increase in strength due to no. of electrons

46
Q

solubility of haloalkanes

A

dissolve in alcohol but not in water

47
Q

why is the carbon-halogen bond generally polar?

A

halogen is much more electronegative

48
Q

nucleophile

A

a species that DONATES an electron pair to form a chemical bond

49
Q

pattern as go down group 7 of speed of hydrolysis

A

increase, as weaker chemical bonds are easier to break

50
Q

useful properties of CFCs (3)

A
  • stable
  • non-flammable
  • non-toxic
51
Q

uses of CFCs

A
  • aerosols
  • fridges
  • aircon
52
Q

how do CFCs break down ozone

A

catalyse the reaction

53
Q

overall equation of ozone breakdown by CFCs

A

O3 + O –> 2O2

54
Q

species responsible for ozone destruction (not CFCs)

A

Nitrogen oxides

55
Q

dehydration reaction - example

A

alcohol –> alkene

56
Q

hydration reaction - example

A

alkene –> alcohol

57
Q

alcohol –> haloalkane reaction - type of reaction

A

substitution

58
Q

haloalkane –> alcohol (type of reaction)

A

hydrolysis

59
Q

alkene –> haloalkane - type of reaction

A

electrophilic addition

60
Q

alcohol –> ketone

A

oxidation

61
Q

alcohol –> aldehyde

A

oxidation

62
Q

aldehyde –> carboxylic acid

A

oxidation

63
Q

alcohol –> carboxylic acid

A

oxidation

64
Q

alkene –> dihaloalkane

A

electrophilic addition

65
Q

alkane –> haloalkane - type of reaction

A

free radical substitution

66
Q

alkene –> alkane

A

hydrogenation

67
Q

conditions for hydration

A

H3PO4 catalyst
300 degrees C
60-70 atm

68
Q

dehydration conditions

A

conc. H2SO4

69
Q

oxidation conditions

A

K2Cr2O7
H2SO4
heat

70
Q

alcohol –> haloalkane (substitution) conditions

A

sodium halide
H2SO4
REFLUX

71
Q

requirement for H-bonding

A

must have a H bonded to either O, F or N

72
Q

London forces

A

instantaneous dipoles - electrons concentrated on one side of molecule, induces dipoles in neighbouring molecules

73
Q

dipole-dipole forces

A

between sigma + and sigma -

74
Q

compared to alkanes, alcohols are…

A

less volatile
higher melting points
greater water solubility

75
Q

why are alcohols less volatile then alkanes

A

permanent dipole means more attractions between molecules ∴ more energy required to overcome

76
Q

bonding in alkanes

A

sigma (σ) - single bonds

saturated hydrocarbon

77
Q

shape of alkanes

A

each c atom surrounded by 4 σ bonds - repulsion creates tetrahedral arrangement and bond angle approx 109.5

78
Q

conditions required for E/Z isomerism

A
  • C=C bond

- different groups on each of the Cs of bond

79
Q

conditions required for cis-trans isomerism

A
  • same as E/Z

BUT must have H as one of bonded groups

80
Q

products of unsymmetrical alkene reaction

A

major + minor

81
Q

markownikoff’s rule

A

when unsymmetrical alkene reacts with hydrogen halide, the H of hydrogen halide attaches itself to the atom with most number of H’s bound to it and least number of C’s

82
Q

why is the major product more stable

A

more alkyl groups attached

positive electron inductive effect, spreading charge out making carbocation more stable

83
Q

bioplastics

A

produced from plant starch

84
Q

structural isotope

A

same molecular formula but different structural formula

85
Q

why are alkanes unreactive

A
  • high enthalpy and low polarity of σ bond
86
Q

why are alkenes reactive

A

low bond enthalpy of π bond

87
Q

as you go down halogens, reactivity of nucleophilic sub of haloalkanes…
- why?

A

increases - reaction rate increases
- bonds get weaker + break more easily
greater atomic radius, more sheilding, weaker attraction, weaker bonds more easily broken

88
Q

3 ways chemists can make polymer disposal more environmentally friendly

A
  • make photodegradable polymers
  • make biodegradable polymers
  • develop ways of sorting AND recycling polymers
89
Q

2 main ways of making ethanol

+ equations

A
  • fermentation of yeast
    C6H12O6 + H2O -> 2C2H5OH + 2CO2
  • hydration of ethene
    C2H2 + H2O -> C2H5OH
90
Q

why are there still concerns about ozone depletion

A
  • long residence time of CFCs

- (not just CFCs) - other ozone depleting substances

91
Q

bond angle and type of molecule in alkenes

A

planar

120

92
Q

restricted movement?

A

atoms attached to the carbons cannot change place

93
Q

3 methods ensuring polymers are used sustainably

- explain

A
  • combustion - burnt to produce energy
  • toxic products - combustion can produce toxic products (HCl) removed and safely disposed of
  • feedstock recycling - broken down into monomers to produce new polymers
94
Q

hydrolysis of haloalkane?

A

when halogen is replaced by OH group = alcohol

95
Q

radical

A

atom/molecule with single unpaired electron

96
Q

why are alkanes not very reactive

A
  • low bond polarity of sigma bond

- high enthalpy of “”

AL. OCR Chemistry (20 decks)

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