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Chemistry > Module 4: Core Organic Chemistry > Flashcards

Module 4: Core Organic Chemistry Flashcards

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
Scale of stability from most stable to least stable
Tertiary - most stable Secondary Primary Methyl - least stable
26
Homologous series definition
Series of organic compounds with the same functional group and each successive member differs by CH2
27
Structural isomers definition
Compounds with the same molecular formula but different structural formulae
28
Stereoisomers definition
Compounds with the same structural formula but with different arrangements in space
29
E/Z isomer definition
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
30
Cis-trans isomers definition
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
31
Homolytic fission definition
The breaking of a covalent bond so that each atom receives one electron from the bonded pair Forming 2 radicals
32
Heterolytic fission definition
The breaking of a covalent bond so that one atom takes both electrons from the bonded pair
33
Radical definition
A species with an unpaired electron
34
Electrophile definition
An electron pair acceptor
35
Nucleophile definition
An electron pair donor
36
Ó bond definition
Overlap of orbitals directly between the bonding atoms
37
Pi bond definition
Sideways overlap of 2 p-orbitals
38
Why is the mp/bp of alkenes lower than alkanes
Rigid double bond prevents the molecules packing together so well so the induced-dipole attractions are slightly weaker
39
What is markownikoff’s rule
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
40
Markownikoff’s rule in simplified terms
Hydrogen likes to be with its friends
41
Limitation of hydration of ethene
Water does not react with alkenes except under extreme conditions
42
Conditions of hydration of ethene
H3PO4 catalyst 300 degrees c 60atm
43
In the lab what is used to carry out electrophilic addition??
Conc H2SO4 H2O
44
Balanced equation of hydrogenation
CH2 = CH2 + H2 ~~> CH3CH3
45
Conditions of hydrogenation
Finely divided nickel catalyst 200 degrees c 10 atm
46
What is another name for hydrogenation
Reduction
47
What is a use of hydrogenation
Used to make margarine from unsaturated vegetable oils
48
Why are alkenes much more reactive than alkanes
Because of low bond enthalpy of the carbon carbon pi bond Makes it easier to break
49
Conditions of bromination
Room temp
50
Why is the double bond of an alkene open to electrophilic attack??
Because they are electron rich
51
Explanation of mechanism of electrophilic addition
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
Properties of polythene Poly(ethane)
Brittle, cheap
53
Uses of polythene Poly(ethane)
Plastic bags Milk bottle crates
54
Properties of poly(propene)
Like polythene but stronger and harder
55
Uses of poly(propene)
Kitchenware
56
Properties of poly(chloroethene)
Flexible and strong
57
Uses of poly(chloroethene)
Rainwater, electrical cable insulation
58
Properties of poly(phenylethene)
Brittle, cheap
59
Uses of poly(phenylethene)
Expanded polystyrene for packaging
60
Properties of poly(tetrafluoroethene)
Very unreactive Low friction Non-stick properties
61
Uses of poly(tetrafluoroethene)
Non-stick saucepan
62
What are synthetic polymers made from??
Oil derived alkenes
63
What happens if synthetic polymers are burnt
Toxic fumes may be formed
64
Are synthetic polymers broken down by bacteria
No because they are non-biodegradable
65
How can chemists reduce damage caused by disposing of polymers and improve sustainability??
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
What do hydrocarbons contain??
Hydrogen and carbon only
67
How many bonds does carbon form?
4
68
How many bonds does hydrogen form??
1
69
How many bonds does oxygen form?
2
70
How many bonds does nitrogen form?
3
71
Aliphatic
Contains straight or branched chains of atoms or non aromatic rings
72
Aromatic
Contain a benzene ring
73
Alicyclics
An aliphatic hydrocarbon which contains a ring of atoms but is it aromatic
74
Explanation of the structure of diamond
Tetrahedral arrangement Carbon forms 4 covalent bonds with other carbon atoms Bond angle 109.5 Giant covalent network Strong covalent bonds throughout
75
Explanation of the structure of graphite
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
Explanation of the structure of graphene
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
Explain the Physical properties of diamond
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
Explain the Physical properties of graphite
High mp/bp Due to strong covalent bonds Soft solids Layers can slide because weak intermolecular forces between Insoluble Conducts electricity
79
Explain the physical properties of graphene
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
What does -ane mean??
No double bond
81
What does -ene mean??
Contains double bond
82
IUPAC Namenciature
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
Why are c-c bonds strong??
Because they are short Because the shared electrons are close to the positive nuclei so there is no repulsion between lone pairs
84
What is the connection between members of a homologous series??
They have similar chemical properties and gradually changing physical properties
85
What does a substitution reaction involve??
Replacing an atom (or groups of atoms) by another atom (or group of atoms
86
Two ways in which covalent bonds can be broken
Homolytic fission Heterolytic fission
87
What does Homolytic fission produce??
Gives 2 free radicals
88
What are free radicals??
A neutral atom or group of atoms which contains an unpaired electron
89
Why are radicals really reactive??
Because of incomplete outershell Cannot be easily isolated
90
What is heterolytic fission??
The breaking of a covalent bond to give a cation and an anion
91
Why does heterolytic fission give both a cation and an anion??
Because electrons are unevenly distributed
92
What is an electrophile??
An electron pair acceptor which is attracted to electron rich molecules
93
What is a nucleophile??
An electron pair donor which is attracted to an atom with partial or full positive charge
94
What is an alkane??
A saturated hydrocarbon
95
General formula for a non cyclic alkane
CnH2n+2
96
Why are alkanes insoluble in water??
Because they are non-polar molecules
97
Why do alkanes float on water?
Because they are less dense than water
98
What are alkanes soluble in??
Organic solvents
99
Colours of the different states of alkanes
CH4 to C4H10 are colourless gases All other alkanes are colourless liquids
100
What is the general trend in mp and bp for alkanes??
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
Why does branching lower the mp and bp of alkanes??
Because molecules pack together less well so the Id id attractions between molecules are weaker
102
Why do alkanes have a tetrahedral shape??
Because the 4 sp3 orbitals of carbon repel each other Bond angle 109.5
103
Why are alkanes generally unreactive??
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
What is a wide use of alkanes??
Widely used as fuels in the home (methane) , for transport (petrol and diesel) and industry (methane and fuel oil)
105
Why is CO toxic??
Because it can bind to haemoglobin and prevent it carrying oxygen round the body
106
Why is there no reaction with cl2 or Br2 in the dark with an alkane??
Because the reaction requires uv light
107
Bromination of methane equation
CH4 + Br2 ~~> CH3Br + HBr
108
3 stages of free radical substitution INITIATION
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
3 stages to free radical substitution PROPAGATION
Each propagation stage consumes a free radical and also generates a free radical
110
3 stages of free radical substitution TERMINATION
Each reaction consumes 2 free radicals which breaks the chain reaction

Chemistry (7 decks)

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