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Chemistry > Basic concepts, alkanes and alkenes > Flashcards

Basic concepts, alkanes and alkenes Flashcards

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1
Q

name of functional group added at the end for alkanes

A
  • ane
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2
Q

name of functional group added at the end for alkenes

A
  • ene
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3
Q

name of functional group added at the end for alcohols

A
  • ol
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4
Q

name of functional group added at the end for esters

A
  • oate
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5
Q

name of functional group added at the end for carboxylic acids

A
  • oic acid
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6
Q

name of functional group added at the end for ketones

A
  • one
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7
Q

name of functional group added at the end for aldehyde

A
  • al
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8
Q

name of functional group added at the end for acid chlorides

A
  • oyl chloride
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9
Q

name of functional group added at the end for amides

A
  • amide
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10
Q

prefix for halogenoalkanes

A

chloro- bromo- or iodo-

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11
Q

prefix for amines

A

amino-

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12
Q

prefix for nitriles

A

cyano-

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13
Q

what is organic chemistry

A

the chemistry of carbon compounds

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14
Q

organic compounds are…

A

found naturally in living or once living things

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15
Q

the simplest organic compounds contain

A

C and H only

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16
Q

what may other organic compounds contain

A

O, N, F, Cl, Br, I and S

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17
Q

how are organic compounds usually bonded

A

covalently

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18
Q

what does carbon always form

A

4 bonds

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19
Q

what does H always form

A

1 bond

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20
Q

what does O always form

A

2 bonds

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21
Q

what does N always form

A

3 bonds

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22
Q

what do F Cl Br and I always form

A

1 bond

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23
Q

what does a structural isomer have

A

same molecular formula but different structural formula

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24
Q

what is a functional group

A

a group of atoms that gives a molecule its characteristic reaction

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25
Q

what are alkanes

A
  • simplest organic compound

- contain c and h with single bonds only

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26
Q

what is a homologous series

A

a series of compounds with the same functional group where each successive member differs by CH2 and have similar chemical properties and a gradual change in physical properties

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27
Q

what is general formula

A

simplest algebraic formula of a member of a homologous series eg alkanes eg CnH2n+2

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28
Q

what is molecular formula

A

actual number of atoms of each element in a molecule eg C2H6O

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29
Q

what is structural formula

A

minimal detail that shows the arrangement of atoms in the molecule eg CH3OCH3
CH3CH2OH

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30
Q

what is displayed formula

A

the structure that shows the relative positioning of the atoms and all the bonds between them

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31
Q

what is skeletal formula

A

a simplified structure. H atoms are removed from what is drawn and C-C bonds are drawn as a line. functional groups remain

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32
Q

what is aliphatic

A

compounds containing C and H joined together in straight chains, branched chains or non aromatic rings

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33
Q

what is alicyclic

A

aliphatic compounds containing C and H jointed together in non aromatic rings

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34
Q

what is aromatic

A

a compound containing a benzene (arene) ring

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35
Q

what is a covalent bond

A

a shared pair of electrons between 2 atoms

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36
Q

for reactions to occur with organic substances…

A

covalent bonds must be broken

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37
Q

homolytic fission

A
  • symmetrical bond breaking
  • one electron from the bonding pair goes to each atom of the bond
  • the products formed have an unpaired electron -> radicals
  • the products are extremely reactive -> uncontrollable reactions
  • each half headed arrow shows the movement of an electron from the bonding pair
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38
Q

heterolytic fission

A
  • unsymmetrical bond breaking
  • both electrons of the bonding pair goes to one atom of the bind
  • positive and negative ions formed
  • each curly arrow shows the movement of a pair of electrons
  • the electron pair moves to the more electronegative element which becomes negatively charged
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39
Q

general formula of alkanes

A

CnH2n+2

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40
Q

cyclic alkanes

A

share the same general formula as alkanes, highly reactive and very unstable due to the strained ring

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41
Q

what are alkanes

A
  • saturated hydrocarbons, contain C and H only with single bonds
  • each C atom is joined to 4 other atoms by single covalent bonds - sigma bonds
42
Q

when do sigma bonds form

A

when orbitals overlap directly between atoms

43
Q

shape around carbon atom in an alkane

A

tetrahedral

  • no lone pairs, electron pairs repel to max separation
  • 109.5°
44
Q

physical properties of alkanes

A
  • low mp and bp - weak instantaneous dipole induced dipole interactions between molecules
  • mp and bp increase with increased chain length - more electrons in the molecules so more/ stronger london forces.
    greater surface area of contact between molecules so more london forces
  • mp and bp decreases with increased branching - molecules pack less well together so less SA of contact between molecules and so less/weaker london forces
45
Q

alkanes and water

A
  • insoluble in water as non polar molecules
  • soluble in organic solvents
  • less dense than water (float / upper layer in a mixture)
46
Q

combustion of alkanes

A

all alkanes burn fully to produce CO2 and H2O

e.g CH4 + 2O2 -> Co2 + H2O

47
Q

what happens if insufficient oxygen is available for combustion

A

Co and C instead of Co2 will be formed

Carbon monoxide is toxic as it binds to haemoglobin which prevents it from carrying o2 round the body

48
Q

RCE of Free radical substitution

A

Reagents : Cl2 or Br2
Conditions : UV light as no reaction occurs in the dark
Equation: eg CH4 + BR2 -> Ch3Br + HBr

49
Q

Initiation stage of free radical substitution

A

Br2 -> 2Br•
Homolytic fission forming Br• radicals. Incredibly reactive and lead to a chain reaction forming many products which is hard to control

50
Q

Propagation stage free radical substitution

A

Ch4 + Br• -> •Ch3 + Hbr
• Ch3 + Br2 -> Ch3Br + Br•
Each propagation step consumes one radical and generates one radical to allow the chain reaction to continue. Many products are possible here as more than one H atom can be substituted

51
Q

termination stage free radical substitution

A

•CH3 + Br• -> Ch3Br
•Ch3 + •Ch3 -> C2H6
each reaction consumes 2 radicals breaking the chain reaction

52
Q

why are radical substitution not a good way to produce a specific product

A
  • propagation steps difficult to control and can lead to a wide range of products as more than 1 H atom can be substituted as well as substitution in different positions
  • Br is regenerated in the 2nd propagation step and so a small number of Br molecules initially can lead to a large number of alkane molecules reacting
  • Radicals are extremely reactive, reacting with almost any species they collide with
53
Q

when is most of the product is made

A

during the propagation steps

54
Q

what is a radical

A

species with an unpaired electron in a mechanism

55
Q

what is substitution

A

one atom / group replaced by another atom / group

56
Q

reactions of cycloalkanes

A

generally just the same as alkanes, with the exception of the very small ones, especially cyclopropane

57
Q

extra reactivity of cyclopropane with uv light

A

with UV light radical substitution the reaction occurs with cl2 or br2 in the same way as a non cyclic alkane

58
Q

extra reactivity of cyclopropane without uv light

A

can undergo addition reactions (alkenes theory) which other alkanes cant.
this can still happen in the presence of light but will get substitution reactions as well

59
Q

what happens without uv light to the ring of cyclopropane

A

the ring is broken due to being very strained - the bond angles are 60 rather than 109.5 when carbon makes its four single bonds

60
Q

why is the ring unstable and how can it be made more stable in cyclopropane

A

the overlap between the atomic orbitals in forming the carbon carbon bonds is poorer than normal and there is considerable repulsion between the bonding pairs. the system becomes more stable if the ring is broken

61
Q

general formula of alkenes

A

cnh2n

62
Q

bonding of alkenes

A

they are unsaturated hydrocarbons so contain c and h only with 1 or more c=c double bonds

63
Q

what do each carbon atom of the double bond form

A

3 sigma bonds. the 4th electron of each carbon is in the P orbital, perpendicular to the plane of the molecule. they overlap sideways above and below the bonding atoms to form the pi bond

64
Q

what is a pi bond

A

sideways overlap of p orbitals and below bonding c atoms

65
Q

what is a sigma bond

A

end on overlap of orbitals between bonding atoms

66
Q

what is the shape around each carbon atom of the double bond

A

trigonal planar

67
Q

c2h4 structure and bonding

A

trigonal planar
3 bonding centres - 2 single 1 double
electron pairs repel to max separation
bond angle 120 degrees

68
Q

restricted rotation as a result of pi bonding

A

restricted rotation about the c=c double bond. rotating this bond would mean breaking the pi bond which would require a lot of energy. keeps the molecule in a rigid flat structure

69
Q

what allows e/z isomerism

A

the restricted rotation keeping it rigid and flat structure

70
Q

length and strength of c=c due to pi bonding

A

c=c is shorter than c-c as 4 electrons attracted by the 2 nuclei of the bond instead of 2. c=c is stronger as it has both pi and sigma bonds giving it a greater total bond enthalpy

71
Q

why are alkenes more reactive

A

relative low bond enthalpy of the pi bond means it is broken more easily

72
Q

why is electrophilic attack possible

A

due to the region of high electron density (pi bond) above and below the bond

73
Q

mp and bp of alkenes

A

increase with increasing chain length. mp and bp lower than corresponding alkanes - alkenes cant pack together as efficiently so fewer London forces are established and less energy required to break

74
Q

alkenes soluble or insoluble

A

insoluble

75
Q

what are the main reactions of alkenes

A

electrophilic addition reactions

76
Q

what is an electrophile

A

molecule or positive ion that can accept a pair of electrons to form a covalent bond

77
Q

what is an addition reaction

A

2 molecules react to form 1

78
Q

why is the double bond open to electrophilic attack

A

it is electron rich

79
Q

hydration alkene

A

reagent: steam
conditions: h3po4 catalyst 300°c 60atm
observations: no visible change

80
Q

bromination alkenes

A

reagent: bromine (aq or inert solvent)
condition: room temperature
observations: orange bromine water turns colourless

81
Q

mechanism for bromination

A
  • br2 is polarised as it approaches double bond
  • curly arrow goes from e- rich to e- deficient area. shows movement of e- pair
  • bond breaking is heterolytic -> both e-s go to 1 atom of the bond
82
Q

reaction with hcl alkenes (also same as HBr or HI)

A

Reagent : HCl gas or conc solution
Conditions: room temperature
observations: no visible change

83
Q

what rule is for unsymmetrical alkenes

A

markownikoff rule with major and minor product

84
Q

explanation of electrophilic addition

A
  • an alkyl group donates electron density to any carbon atom to which it is attached (alkyl groups are electron donating)
  • this means that the carbonation with the most alkyl groups attached will be the most stable
  • the electron donating alkyl groups stabilise the positive charge by allowing it to be more spread out
85
Q

reasoning for something being the major product

A

…… is the major product due to the carbocation intermediate it forms via being more stable

86
Q

hydrogenation alkenes

A

used in the production of margarine from vegetable oil

reagent: hydrogen gas
conditions: nickel catalyst
observations: no visible change

87
Q

equation for hydrogenation

A

c2h4 + h2 -> c2h6

88
Q

addition polymerisation

A

many monomers join together to form a polymer (long chain molecule)
pi bonds break and many molecules join together

89
Q

synthetic polymers

A
  • made from oil derived alkenes and replacing many natural materials
  • non biological so difficult to dispose of
  • use up landfill space
  • produce toxic fumes when burnt
90
Q

how can sustainability be improved

A
  • burn polymers to produce heat energy for electricity generation. this conserves fossil fuel supplies
  • removal of toxic waste products from burning
    halogenated plastics form HCl on burning, removed with a base
  • recycling to form new products
  • use polymers as an organic feedstock for the production of new plastics and organic chemicals. monomers and other substances can be reclaimed from waste polymers resulting in mixtures similar to crude oil
  • develop biodegradable and photodegradable polymers. broken down by microorganisms or have bonds that are weakened when exposed to light.
  • develop polymers made from plant based materials eg maize and starch to reduce demand of finite oil reserves
91
Q

ether properties and uses

A

brittle and cheap

plastic bags

92
Q

polypropene properties and uses

A

stronger than polyethylene

used for plastic kitchenware eg buckets

93
Q

polychloroethene uses

A

flexible and strong

drain pipes and phone cables

94
Q

phenylethene properties and uses

A

brittle and cheap

polystyrene - packaging and cups

95
Q

polytetrafluoroethene properties and uses

A

non stick frying pans

teflon

96
Q

what is a stereoisomer

A

compounds with the same structural formula but with a different arrangement in space

97
Q

e/z isomer definition

A

an example of stereoisomers. restricted rotation about the c=c double bond and 2 different groups attached to each carbon atom of the c=c double bonds

98
Q

cis-trans isomers

A

a special case of e/z isomerism where 2 of the groups attached to each carbon atom of the c=c double bond are the same

99
Q

for e/z isomerism must have

A

restricted rotation and 2 different atoms or groups

100
Q

trans

A

across (E)

101
Q

cis

A

same size Z

Chemistry (17 decks)

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