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Chemistry > Module 4: Core Organic Chemistry > Flashcards

Module 4: Core Organic Chemistry Flashcards

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1
Q

What is an Alkene??

A

An unsaturated hydrocarbon which contains one or more carbon-carbon double bonds

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2
Q

What is the general formula for a non-cyclic alkene with one double bond

A

CnH2n

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3
Q

Physical properties of alkenes

A

Similar mass to alkanes due to induced dipole attraction between molecules

Mp and bp tend to be slightly lower than alkanes because rigid double bonds prevents the molecules packing together

So the instantaneous induced dipole attractions are slightly weaker

Insoluble in water

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4
Q

What is a double bond??

A

The sideways overlap of p orbitals above and below bonding carbon atoms

And

The overlap of orbitals between the bonding atoms

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5
Q

What are the 3 bonding centres in a carbon

A

2 single bonds

1 double bond

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6
Q

Structure of alkane

A

The four sp3 orbitals repel each other into a tetrahedral arrangement

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7
Q

Structure of an alkene

A

Three sp2 orbitals repel each other into a planar arrangement

2p orbital lies at right angles to them

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8
Q

How is a double covalent bond formed??

A

Covalent bonds formed by overlap of orbitals

Sp2 orbital from each carbon overlaps to form single c-c bond

Resulting bond is a sigma bond

Two 2p orbitals also overlap to form a second bond

For max overlap the 2p orbitals are in line this forms the strong bond

Gives rise to the planar arrangement around c=c bonds

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9
Q

Consequences of pi bonding

A

No rotation possible round pi bond without breaking pi bond

C=C will be shorter than c-c

C=C greater bond energy than c-c

Alkenes more reactive

Pi orbital exposed region of high electron density

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10
Q

Why is c=c shorter than c-c

A

Because there are 4 shared electrons attracting positive nuclei rather than 2

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11
Q

Why does C=C have a greater bond energy than c-c

A

Because the pi bond is weaker than the sigma bond

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12
Q

What is stereoisomerism??

A

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

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13
Q

2 types of stereoisomers

A

E/Z isomerism

Optical isomerism

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14
Q

What is E/Z isomerism

A

Each carbon of the double bond must be bonded to two different atoms or groups

Different compounds that will have different properties

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15
Q

What does E stand for??

A

Entgegen (opposite)

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16
Q

What does Z stand for??

A

Zusammen (together)

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17
Q

When are CIP priority rules used??

A

Can be used to determine whether an isomer is E or Z when there are 3 or 4 different groups

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18
Q

What is a Cis trans isomer??

A

A special case of E/Z isomerism where two of the groups attached to each carbon atom of the c=c double bond are the same

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19
Q

Trans

A

Across (E)

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20
Q

Cis

A

same side (z)

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21
Q

Observation of addition of bromine or bromine in an inert solution

A

Orange bromine water goes colourless

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22
Q

What is addition of bromine a good test for??

A

Alkenes

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23
Q

How does electrophilic addition work?? Example using bromine

A

Br2 (or other element) is polarised by the high electron density of the pi bond in the alkene

The br-br bond and c-c pi bond break by heterolytic fission

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24
Q

Why is a major product more stable

A

Because compared to hydrogen carbon has an electron pushing inductive effect

Helps to stabilise a positive charge next to it, the two surrounding c’s help to stabilise the positive change

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25
Q

Scale of stability from most stable to least stable

A

Tertiary - most stable

Secondary

Primary

Methyl - least stable

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26
Q

Homologous series definition

A

Series of organic compounds with the same functional group and each successive member differs by CH2

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27
Q

Structural isomers definition

A

Compounds with the same molecular formula but different structural formulae

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28
Q

Stereoisomers definition

A

Compounds with the same structural formula but with different arrangements in space

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29
Q

E/Z isomer definition

A

An example of stereoisomerism

Restricted rotation about the c=c double bond

2 different groups attached to each carbon atom of the c=c bond

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30
Q

Cis-trans isomers definition

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

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31
Q

Homolytic fission definition

A

The breaking of a covalent bond so that each atom receives one electron from the bonded pair

Forming 2 radicals

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32
Q

Heterolytic fission definition

A

The breaking of a covalent bond so that one atom takes both electrons from the bonded pair

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33
Q

Radical definition

A

A species with an unpaired electron

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34
Q

Electrophile definition

A

An electron pair acceptor

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35
Q

Nucleophile definition

A

An electron pair donor

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36
Q

Ó bond definition

A

Overlap of orbitals directly between the bonding atoms

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37
Q

Pi bond definition

A

Sideways overlap of 2 p-orbitals

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38
Q

Why is the mp/bp of alkenes lower than alkanes

A

Rigid double bond prevents the molecules packing together so well so the induced-dipole attractions are slightly weaker

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39
Q

What is markownikoff’s rule

A

When a molecule adds across a double bond

The least electronegative atom or group adds to the carbon with the most hydrogen atoms already attached

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40
Q

Markownikoff’s rule in simplified terms

A

Hydrogen likes to be with its friends

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41
Q

Limitation of hydration of ethene

A

Water does not react with alkenes except under extreme conditions

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42
Q

Conditions of hydration of ethene

A

H3PO4 catalyst

300 degrees c

60atm

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43
Q

In the lab what is used to carry out electrophilic addition??

A

Conc H2SO4

H2O

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44
Q

Balanced equation of hydrogenation

A

CH2 = CH2 + H2 ~~> CH3CH3

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45
Q

Conditions of hydrogenation

A

Finely divided nickel catalyst

200 degrees c

10 atm

46
Q

What is another name for hydrogenation

A

Reduction

47
Q

What is a use of hydrogenation

A

Used to make margarine from unsaturated vegetable oils

48
Q

Why are alkenes much more reactive than alkanes

A

Because of low bond enthalpy of the carbon carbon pi bond

Makes it easier to break

49
Q

Conditions of bromination

A

Room temp

50
Q

Why is the double bond of an alkene open to electrophilic attack??

A

Because they are electron rich

51
Q

Explanation of mechanism of electrophilic addition

A

Bromine is polarised as it approaches the double bond

Curley arrow goes from electron rich area to electron deficient area

Br-Br and Pi bond breaking is heterolytic

Both electrons go to 1 atom of the bond ( +ve and -ve ion formed)

52
Q

Properties of polythene

Poly(ethane)

A

Brittle, cheap

53
Q

Uses of polythene

Poly(ethane)

A

Plastic bags

Milk bottle crates

54
Q

Properties of poly(propene)

A

Like polythene but stronger and harder

55
Q

Uses of poly(propene)

A

Kitchenware

56
Q

Properties of poly(chloroethene)

A

Flexible and strong

57
Q

Uses of poly(chloroethene)

A

Rainwater, electrical cable insulation

58
Q

Properties of poly(phenylethene)

A

Brittle, cheap

59
Q

Uses of poly(phenylethene)

A

Expanded polystyrene for packaging

60
Q

Properties of poly(tetrafluoroethene)

A

Very unreactive
Low friction
Non-stick properties

61
Q

Uses of poly(tetrafluoroethene)

A

Non-stick saucepan

62
Q

What are synthetic polymers made from??

A

Oil derived alkenes

63
Q

What happens if synthetic polymers are burnt

A

Toxic fumes may be formed

64
Q

Are synthetic polymers broken down by bacteria

A

No because they are non-biodegradable

65
Q

How can chemists reduce damage caused by disposing of polymers and improve sustainability??

A

Burning at high temps to produce energy - can be used to generate electricity
~~> conserves fossil fuels supplies

Remove toxic waste when they are burnt
(E.g. by using a base)

Developing biodegradable and photodegradable polymers

Use as organic feedstock for the production of plastics

Developing ways of making polymers from plant based materials
~~> allows reduction of oil use

66
Q

What do hydrocarbons contain??

A

Hydrogen and carbon only

67
Q

How many bonds does carbon form?

A

4

68
Q

How many bonds does hydrogen form??

A

1

69
Q

How many bonds does oxygen form?

A

2

70
Q

How many bonds does nitrogen form?

A

3

71
Q

Aliphatic

A

Contains straight or branched chains of atoms or non aromatic rings

72
Q

Aromatic

A

Contain a benzene ring

73
Q

Alicyclics

A

An aliphatic hydrocarbon which contains a ring of atoms but is it aromatic

74
Q

Explanation of the structure of diamond

A

Tetrahedral arrangement

Carbon forms 4 covalent bonds with other carbon atoms

Bond angle 109.5

Giant covalent network

Strong covalent bonds throughout

75
Q

Explanation of the structure of graphite

A

Carbon forms 3 covalent bonds with other covalent atoms

4th electron of each atom is delocalised

Layers of interlinked hexagons

Bond angle = 120

Strong covalent bonds in each layer

Weak London forces

76
Q

Explanation of the structure of graphene

A

Carbon forms 3 covalent bonds with other carbon atoms

4th electron in each carbon is delocalised

Single sheets of interlinked hexagons

1 atom thick

Bond angle = 120

Strong covalent bonds throughout

77
Q

Explain the Physical properties of diamond

A

High mp/bp

Strong and hard

This is because strong covalent bonds require a lot of energy to break

Insoluble

Do not conduct electricity because there are no free electrons or ions to carry a current

78
Q

Explain the Physical properties of graphite

A

High mp/bp
Due to strong covalent bonds

Soft solids
Layers can slide because weak intermolecular forces between

Insoluble

Conducts electricity

79
Q

Explain the physical properties of graphene

A

Conducts electricity as 4th electron from each carbon is delocalised and can move

High strength
Due to a network of strong covalent bonds needed to be broken

80
Q

What does -ane mean??

A

No double bond

81
Q

What does -ene mean??

A

Contains double bond

82
Q

IUPAC Namenciature

A

A systematic name has a root that tells us the longest unbranched hydrocarbon chain or ring

The syllable after the root tells us if there are any double bonds

83
Q

Why are c-c bonds strong??

A

Because they are short

Because the shared electrons are close to the positive nuclei so there is no repulsion between lone pairs

84
Q

What is the connection between members of a homologous series??

A

They have similar chemical properties and gradually changing physical properties

85
Q

What does a substitution reaction involve??

A

Replacing an atom (or groups of atoms) by another atom (or group of atoms

86
Q

Two ways in which covalent bonds can be broken

A

Homolytic fission

Heterolytic fission

87
Q

What does Homolytic fission produce??

A

Gives 2 free radicals

88
Q

What are free radicals??

A

A neutral atom or group of atoms which contains an unpaired electron

89
Q

Why are radicals really reactive??

A

Because of incomplete outershell

Cannot be easily isolated

90
Q

What is heterolytic fission??

A

The breaking of a covalent bond to give a cation and an anion

91
Q

Why does heterolytic fission give both a cation and an anion??

A

Because electrons are unevenly distributed

92
Q

What is an electrophile??

A

An electron pair acceptor which is attracted to electron rich molecules

93
Q

What is a nucleophile??

A

An electron pair donor which is attracted to an atom with partial or full positive charge

94
Q

What is an alkane??

A

A saturated hydrocarbon

95
Q

General formula for a non cyclic alkane

A

CnH2n+2

96
Q

Why are alkanes insoluble in water??

A

Because they are non-polar molecules

97
Q

Why do alkanes float on water?

A

Because they are less dense than water

98
Q

What are alkanes soluble in??

A

Organic solvents

99
Q

Colours of the different states of alkanes

A

CH4 to C4H10 are colourless gases

All other alkanes are colourless liquids

100
Q

What is the general trend in mp and bp for alkanes??

A

Mps and bps increase with chain length as the total number of electrons in each molecule increases

So id id attractions between molecules gets stronger

101
Q

Why does branching lower the mp and bp of alkanes??

A

Because molecules pack together less well so the Id id attractions between molecules are weaker

102
Q

Why do alkanes have a tetrahedral shape??

A

Because the 4 sp3 orbitals of carbon repel each other

Bond angle 109.5

103
Q

Why are alkanes generally unreactive??

A

C-C and C-H bonds are strong and hard to break

C-C and C-H bonds are non-polar so are not attacked by polar regions

104
Q

What is a wide use of alkanes??

A

Widely used as fuels in the home (methane) , for transport (petrol and diesel) and industry (methane and fuel oil)

105
Q

Why is CO toxic??

A

Because it can bind to haemoglobin and prevent it carrying oxygen round the body

106
Q

Why is there no reaction with cl2 or Br2 in the dark with an alkane??

A

Because the reaction requires uv light

107
Q

Bromination of methane equation

A

CH4 + Br2 ~~> CH3Br + HBr

108
Q

3 stages of free radical substitution

INITIATION

A

Bonds broken by light energy (photodissociation)

Homolytic fission occurs - symmetrical bond breaking

Br is a radical and this will lead to a chain reaction because radicals are v reactive

109
Q

3 stages to free radical substitution

PROPAGATION

A

Each propagation stage consumes a free radical and also generates a free radical

110
Q

3 stages of free radical substitution

TERMINATION

A

Each reaction consumes 2 free radicals which breaks the chain reaction

Chemistry (7 decks)

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