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A Level Chemistry > Module 4 Section 1: Basic Concepts and Hydrocarbons > Flashcards

Module 4 Section 1: Basic Concepts and Hydrocarbons Flashcards

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1
Q

All the formula types and what they show

A

General formula - algebraic formula that describes any member or family of compound
Empirical - the simplest ratio of atoms of each element in a compound (cancel numbers down if possible)
Molecular - actual number of atoms of each element in a molecule
Structural - shows atoms carbon by carbon, with the attached hydrogens and functional groups (structure of each section)
Displayed - shows how all the atoms are arranged and all the bonds between them (like ball and stick model)
Skeletal - shows the bonds of carbon skeleton only, with any functional groups. The hydrogen and carbon atoms aren’t shown (zig zag, handy for drawing large complicated structures)

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2
Q

all the formulas for butan - 1 - ol

A

General: CnH(2n+1)OH

Empirical: C4H10O ( ethane, C2H6, is CH3

Molecular: C4H10O

Structural: CH3,CH2,CH2,CH2,OH or CH3(CH2)3OH

Displayed: ball and stick type ( moly mod )

Skeletal: \ /\ /OH

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3
Q

What is a homologous series

A

A group of compounds that have the same functional group and general formula
Consecutive (/successive) members of a homologous series differ by -CH2

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4
Q

What is the simplest homologous series called

A

Simplest is the alkanes
These are straight chain molecules that contain carbon and hydrogen atoms only

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5
Q

General formula for alkanes

A

CnH(2n+2)

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6
Q

What are the first 10 alkanes

A

1 carbon atom: methane CH4
2 carbon atoms: ethane C2H6
3 carbon atoms: propane C3H8
4 carbon atoms: butane C4H10
5 carbon atoms: pentane C5H12
6 carbon atoms: hexane C6H14
7 carbon atoms: heptane C7H16
8 carbon atoms: octane C8H18
9 carbon atoms: nonane C9H20
10 carbon atoms: decane C10H22

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7
Q

How to name any organic compound

A

1) Count the carbon atoms in the longest continuous chain which gives you the stem
2) The main functional group of the molecule usually gives you the end of the name
3) Number the longest carbon chain so that the main functional group has the lowest possible number, if there’s more than one longest chain, pick the one with the most side chains
4) Any side chains or less important functional groups are added as prefixes at the start of the name, put them in alphabetical order with the number of the carbon atom each it attached to
5) If there is more than one identical side chain of functional group, use di- (2), tri- (3) or tetra- (4) before that part of the name - but ignore this when working in alphabetical order

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8
Q

Prefix, suffix and example for alkanes

A

Prefix or suffix: -ane
E.g. propane

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9
Q

Prefix, suffix and example for branched alkanes

A

Prefix or suffix: alkyl-, -yl
E.g. methyl propane

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10
Q

Prefix, suffix and example for alkenes

A

Prefix, suffix: -ene
E.g. propene

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11
Q

Prefix, suffix and example for haloalkanes

A

Prefix, suffix: chloro-, bromo-, iodo-, ( no suffix )
Chloroethane

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12
Q

Prefix, suffix and example for alcohols

A

Prefix, suffix: hydroxy-, -ol
E.g. ethanol

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13
Q

Prefix, suffix and example for aldehydes

A

Prefix, suffix: oxo-, -al
E.g. ethanal

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14
Q

Prefix, suffix and example for ketones

A

Prefix, suffix: oxo-, -one
E.g. propanone

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15
Q

Prefix, suffix and example for cycloalkanes

A

Prefix, suffix: cyclo-, -ane
E.g. cyclohexane

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16
Q

Prefix, suffix and example for Arenes

A

Prefix, suffix: benzene
E.g. ethylbenzene

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17
Q

Prefix, suffix and example for esters

A

Prefix, suffix: oxycarbonyl-, -alkyl, -anoate
E.g. propyl ethanoate

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18
Q

Prefix, suffix and example for Carboxylic acid

A

Prefix, suffix: Carboxy-, -oic acid
E.g. ethanoic acid

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19
Q

Difference between aromatic and aliphatic compounds

A

Aromatic compounds contain a benzene ring
Aliphatic compounds contain carbon and hydrogen joined together in straight chains, branched chains or non - aromatic chains
If an aliphatic compound contains a ( non - aromatic ) ring, then it can be called alicyclic

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20
Q

Difference between saturated and unsaturated compounds

A

Saturated compounds only contain carbon - carbon single bonds - like alkanes
Unsaturated compounds can have carbon - carbon double bonds, triple bonds or aromatic groups

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21
Q

What is an alkyl group

A

An alkyl group is a fragment of a molecule with general formula CnH2n+1
( looks like a bit of an alkane attached to the side of the chain )

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22
Q

What are isomers and what are the two we need to know

A

Two molecules are isomers of one another if they have the same molecular formula but the atoms are arranged differently
The two isomers we need to know are structural isomers and stereoisomers

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23
Q

Structural isomers and the 3 types

A

In structural isomers, the atoms are connected in different ways
Although the molecular formula is the same, the structural formula is different
3 types include: chain isomers, positional isomers and functional group isomers

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24
Q

Chain isomers and examples

A

The carbon skeleton can be arranged differently - e.g. as a straight chain, or branched in different ways
These isomers have similar chemical properties
But their physical properties, like boiling point , will be different because of the change in shape of the molecule
E.g. butane and methylpropane are chain isomers of eachother

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25
Q

Positional isomers and examples

A

The skeleton and the functional group could be the same, only with the functional group attached to a different carbon atom
These also have different physical properties, and the chemical properties might be different too
E.g butan - 1 -ol and butan - 2 - ol

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26
Q

Functional group isomers and examples

A

The same atoms can be arranged into different functional groups
These can have very different chemical properties
E.g. butanoic acid and methyl propanoate

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27
Q

Prefix, suffix and example for acid halide

A

Prefix/ suffix: halocarbonyl-, -oyl halide
e.g. ethanoyl chloride

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28
Q

Prefix, suffix and example for amides

A

Prefix/ suffix: carbamoyl-, -amide
e.g. methanamide

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29
Q

Prefix, suffix and example for nitrile

A

Prefix/ suffix: cyano-, -nitrile
e.g. propanenitrile

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30
Q

Prefix, suffix and example for thiol

A

Prefix/ suffix: sulfanyl-, -thiol
e.g. propanethiol

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31
Q

Prefix, suffix and example for amine

A

Prefix/ suffix: amino-, -amine
e.g. ethylamine

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32
Q

Prefix, suffix and example for sulfide

A

Prefix/ suffix: (no prefix), -sulfanyl (so this is for when secondary)
e.g. hexanethiol

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33
Q

Prefix, suffix and example for ether

A

Prefix/ suffix: (no prefix), -oxy-
e.g. methoxybutane

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34
Q

What is a functional group?

A

A group of atoms in a molecule responsible for the characteristic reactions of the compound

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35
Q

What is the functional group priority list

A

Carboxylic acid
Ester
Acid halide
Amide
Nitrile
Aldehyde
Ketone
Alcohol
Thiol
Amine
Imine
Ether
Sulfide
Alkene
Alkyne
Haloalkane
Nitro

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36
Q

What is heterolytic fission

A

The bond breaks unevenly with one of the bonded atoms receiving both electrons from the bonded pair
Two different substances are formed - a positively charged cation ( X+ ), and a negatively charged anion ( Y- )

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37
Q

What is homolytic fission

A

The bond breaks evenly and each bonding atom receives one electron from the bonded pair
Two electrically uncharged radicals are formed

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38
Q

What are radicals

A

Particles that have an unpaired electron
They are shown in mechanisms by a big dot next to the molecular formula
Radicals are very reactive due to the unpaired electron

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39
Q

How do halogens react with alkanes

A

Halogens react with alkanes in photochemical reactions
These are started by light - this requires ultraviolet light to start
A hydrogen atom is substituted by chlorine or bromine
This is a free radical substitution reaction
E.g. CH4 + Cl2 —UV—> CH3Cl + HCl

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40
Q

What are the three stages of reaction mechanism

A

Initiation reactions
Propagation reactions
Termination reactions

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41
Q

What happens in initiation reactions

A

Free radicals are produced by homolytic fission
UV provides energy to break Cl-Cl bond - this is photodissociation: Cl2 —UV-> 2Cl
The atom becomes a highly reactive free radical, Cl •, because of its unpaired electron

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42
Q

What happens in propagation reactions

A

Free radicals are used up and created in a chain reaction
Cl • attacks a methane molecule: Cl • + CH4 -> •CH3 + HCl
The new methyl free radical, •CH3, can attack another Cl2 molecule: •CH3 + Cl2 -> CH3Cl + Cl •
The new Cl • can attack another CH4 molecule, and so on, uncial all the Cl2 or CH4 molecules are gone

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43
Q

What happens in termination reactions

A

Free radicals are mopped up
If two free radicals join together, they make a stable molecule
There are lots of possible termination reactions
E.g.
Cl • + •CH3 -> CH3Cl
•CH3 + •CH3 -> C2H6

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44
Q

What’s the problem with free radical substitution

A

You do not always get the desired product, instead you get a mixture of products
E.g. if you’re trying to make chloromethane and there’s too much chlorine in the reaction mixture, some of the remaining hydrogen atoms on the chloromethane molecules will be swapped for chlorine atoms
The propagation reactions happens again to make dichloromethane, again to make trichloromethane and again to make tetrachloromethane

Also, it can take place at any point along the carbon chain
So a mixture of isomers can be formed e.g. reacting propane with chlorine will produce a mixture of 1-chloropropane and 2-chloropropane

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45
Q

How to reduce the problems with free radical substitution

A

Have an excess of methane so there’s a greater chance of a chlorine radical colliding only with a methane molecule and not a chloromethane molecule

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46
Q

What are alkenes and what is their structure

A

Unsaturated compounds with the general formula CnH2n
They are hydrocarbons as they are made of carbon and hydrogen atoms only
Alkenes all have at least one C=C double covalent bond
C=C double bonds make the molecule unsaturated as they can make more bonds with extra atoms in addition reactions

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47
Q

What is a σ bond and when is it formed

A

σ bond ( sigma bond ) is formed by two s orbitals direct overlap
The two s orbitals overlap in a straight line - gives the highest possible electron density between the two nuclei
This is is a single covalent bond
The high electron density between the nuclei means there is a strong electrostatic attraction between the nuclei and the shared pair of electrons
This means σ bonds have a high bond enthalpy - strongest type of covalent bonds

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48
Q

What are π bonds

A

π ( pi ) bonds are formed by sideways overlap of two adjacent p orbitals
It’s got two parts: one above and below the molecular axis
This is because the p orbitals which overlap are dumb bell shaped

π bonds are much weaker than σ bonds as the electron density is spread out above and below the nuclei
This means the electrostatic attraction between the nuclei and the shared pair of electrons is weaker, so π bonds have relatively low bond enthalpy

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49
Q

How are alkanes less reactive than alkenes

A

Alkanes only contain C - C and C - H σ bonds, which have a higher bond enthalpy and so are difficult to break
The bonds are also non-polar so they don’t attract nucleophiles or electrophiles
This means that they don’t react easily

50
Q

How are alkenes more reactive than alkanes

A

Alkenes are more reactive than alkanes because the C = C bond contains both a σ bond and a π bond
The C = C double bond contains four electrons so has a high electrons density and the π bond also sticks out above and below the rest of the molecule
This means the π bond is likely to be attacked by electrophiles
The low bond enthalpy of the π bond also contributes to the reactivity of alkenes
Because the double bond’s so reactive, alkenes are good starting points for making other organic compounds or petrochemicals

51
Q

How are carbon atoms in a C =C bond arranged

A

Carbon atoms in a C = C bond and atoms bonded to these carbons all lie in the same plane ( they’re planar )
This means that they are trigonal planar - atoms attached to each double-bonded carbon are at the corners of an imaginary equilateral triangle
However, smaller molecules like ethene are completely planar whereas in larger alkenes, only the C=C unit is planar

52
Q

Why can’t the C=C rotate

A

The atoms can’t rotate around them like they can around single bonds
This is because of the way the p orbitals overlap to form a pi bond
This means they are rigid and don’t bend much either
However, the atoms can still rotate around the single bonds in the molecule
This restricted rotation around the C=C causes alkenes to form stereoisomers

53
Q

What are stereoisomers

A

Have the same structural formula but a different arrangement in space
This happens because of the lack of rotation around the double bond
They occur when the two double bonded carbon atoms each have two different atoms or groups attached to them
One these isomers is called the E-isomer and the other is called the Z-isomer

54
Q

Difference between E and Z isomers

A

The Z-isomer has the same groups either both above or both below the double bond
The E-isomer has the same groups positioned across the double bond

55
Q

E/Z isomers of But-2-ene

A

Z isomer: same groups are both above double bond - Z-but-2-ene
H3C CH3
\ /
C = C
/ \
H H

E isomer: same groups across double bond - E-but-2-ene
H CH3
\ /
C = C
/ \
H3C H

56
Q

What does the Z and E mean is stereoisomerism

A

Z stands for Zusammen: German for “together”
E stand for Entgegen: German for “opposite”

57
Q

What are the CIP rules and how are these used

A

Cahn-Ingold-Prelog rule can work out which is the E isomer and which is the Z isomer for any alkene

58
Q

How to use the CIP rules

A
  1. Look at the atoms directly bonded to each of the C=C atoms
    The atom with the higher ATOMIC NUMBER on each carbon is given higher priority
  2. You can assign the isomers as E and Z by looking at how the groups of the same priority are arranged
  3. You must be cautious if doing this for an alkene with only 3 different groups
    The E/Z system gives the positions of the highest priority group on each carbon, which aren’t always the matching groups
59
Q

Using the CIP rules for 1-bromo-1-chloro-2-fluoro-ethene

A

F Cl
\ /
C = C
/ \
H Br
1. Atoms attached to carbon one are bromine ( AN 35 ) and chlorine ( AN 17 ), bromine is higher priority
Atoms attached to carbon 2 are fluorine ( AN 9 ) and hydrogen ( AN 1 ), fluorine is higher priority
2. Higher priority groups are positioned across double bond so this is an E isomer

60
Q

When may you have to look further along the chain to decide between E/Z isomers

A

If the atoms directly to the carbon are the same then you may have to look at the next atom in the group to work out priority

CH3
|
CH2     Cl
  \        /
   C = C
  /         \

H3C Br

The first carbon is directly bonded to two carbon atoms, so you need to go further along the chain
The methyl carbon only has hydrogen atoms but the ethyl carbon is attached to another carbon atom so it has priority

61
Q

What are cis-trans isomers

A

If the carbon atoms have at least one group in common ( like but-2-ene ), then you can call them cis or trans ( as well as E or Z )

62
Q

What’s the difference between cis and trans isomers

A

Cis means the same groups are on the same side of the double bond
Trans means the same groups are on the opposite sides of the double bond

So E-but-2-ene can be called trans-but-2-ene and Z-but-2-ene can be called cis-but-2-ene

63
Q

When can’t the cis-trans method work

A

If the carbon atoms both have totally different groups attached to them

64
Q

What happens in an electrophilic addition reaction

A

The alkene double bond opens up and atoms are added to the carbon atoms

65
Q

Why do electrophilic addition reactions occur

A

They happen because the double bond has got lots of electrons and is easily attacked by electrophiles

66
Q

What are electrophiles

A

They are electron pair acceptors - they are usually short of electrons
This means they are attracted to areas where there are lots of electrons

67
Q

What type of atoms or molecules are electrophiles

A

Positively charged ions ( e.g. H+ NO2+ )
Polar molecules ( partially positive atom is attracted to electrons
Polarisable bonds ( e.g. Br-Br, Cl-Cl )

68
Q

What happens when hydrogen is added to alkenes

A

Adding hydrogen to C=C bonds produces alkanes
E.g. ethene will react with hydrogen gas in an addition reaction to produce ethane
This needs a nickel catalyst and a temperature of 150°C

69
Q

What do halogens react with alkenes to make and what type of reaction is this

A

Halogens react with alkenes to form dihaloalknes
Halogens add across the double bond and each carbon atoms originally in the bond will bond to a halogen atoms
This is electrophilic addition reaction

70
Q

General equation for hydrogen and alkenes

A

H2C=CH2 + H2 = CH3CH3

71
Q

General equation for halogens and alkenes

A

H2C=CH2 + X2 = CH2XCH2X

72
Q

Mechanism for the creation of a dihaloalkanes from alkenes ( electrophilic addition )

A

E.g. ethene and bromine molecules
Double bond repels electrons in Br2 which polarises Br - Br
Double bond donates electron pair to delta positive Br
Heterolytic fission of Br2 - closer Br gives up bonding electrons to the delta negative Br and bonds to carbon atom
Creates positively charged carbocation ( intermediate)
Br donates lone pair to carbocation, bonding to it, making 1,2-dibromoethane

73
Q

What is a carbocation

A

Organic ion containing a positively charged carbon atom

74
Q

How to test for carbon double bonds

A

When you shake an alkene with orange bromine water, the solution quickly decolourises
This is because the bromine is added across the double bond to form a colourless dibromoalkane

75
Q

What type of molecules or atoms are nucleophiles

A

Anions ( Br-, OH- )
Pi bonds ( C=C )
Atoms with lone pairs ( H2O, NH3 )

76
Q

How are alcohols made by steam hydration

A

Alkenes can be hydrated by steam at 300°C and a pressure of 60-70 atm
This needs a solid phosphoric acid catalyst
The reaction is reversible and the yield is low ( with ethene it’s 5% ) but the gas can be recycled which increases the yield much more

77
Q

What are alkanes

A

Saturated hydrocarbons
General formula CnH2n+2
They are hydrocarbons as they only have carbon and hydrogen atoms

78
Q

Why are alkanes saturated

A

Every carbon atom in an alkane has four single bonds with other atoms
All the carbon-carbon bonds are single bonds

79
Q

What shape are alkane molecules around each carbon

A

Each atom has four pairs of bonding electrons around it
They all repel each other equally so the molecule forms a tetrahedral shape around each carbon
Each bond angle is 109.5°

80
Q

What inter/intramolecular forces are present in alkanes

A

Alkanes have covalent bonds inside the molecules
Between the molecules, there are induced dipole-dipole interactions which hold them together

81
Q

Trends with size of alkanes and boiling points

A

Smallest alkanes are gases at room temperature and pressure - very low boiling points
Larger alkanes are liquids at RTP - higher boiling points
The longer the carbon chain, the stronger induced dipole-dipole interactions
This is because there’s more surface contact and more electrons to interact

82
Q

How does the boiling point increase with chain length

A

As the molecules get longer, it takes more energy to overcome the induced dipole-dipole interactions, and the boiling points rises

83
Q

Why do branched alkanes have a lower boiling points than their straight chain isomers

A

Branched alkanes can’t pack closely together (so there is less surface contact) and they have smaller molecular surface areas - so the induced dipole-dipole interactions are reduced

84
Q

What happens when you burn alkanes in oxygen

A

A combustion reaction occurs which produces carbon dioxide and water

85
Q

What state do combustion reactions occur at

A

They happen between gases, so liquid alkanes have to be vaporised first
Smaller alkanes turn into gases more easily, so they’ll burn more easily too

86
Q

Why do larger alkanes release more energy

A

Release more energy per mole because they have more bonds to react

87
Q

Why are alkanes so good as fuels

A

They release lots of energy when they burn

88
Q

How to use volumes to work out combustion equations

Example: 30cm3 of hydrocarbon X combusts completely with 240cm3 of oxygen. 150cm3 of carbon dioxide is produced, what is the molecular formula of hydrocarbon X?

A

Example: 30cm3 of hydrocarbon X combusts completely with 240cm3 of oxygen. 150cm3 of carbon dioxide is produced, what is the molecular formula of hydrocarbon X?
Using volumes provided, write a reaction equation 30X + 240O2 = 150CO2 + ?H2O
Can be simplified to X + 8O2 = 5CO2 + nH2O
8 moles of oxygen reactions to form 5 moles of CO2 and n moles of H2O. This means that n = (8x2) - (5x2) = 6
Combustion reaction is now X + 8O2 = 5CO2 + 6H2O - can be used to identify X
All carbon atoms from X form carbon dioxide molecules, and all hydrogen atoms from X are used to form water, so the number of carbon atoms in X is 5 and the number of hydrogen atoms is 12
Molecular formula of X is C5H12

89
Q

What happens when the alkane is burned in limited oxygen

A

The alkanes will still burn, but it will produce carbon monoxide and water

90
Q

How is carbon monoxide poisonous

A

The oxygen in your bloodstream is carried around by haemoglobin
Carbon monoxide is better at binding to haemoglobin than oxygen is, so it binds to the haemoglobin in your bloodstream before the oxygen can
This means less oxygen can be carried around your body, leading to oxygen deprivation
At very high concentration, carbon can be fatal

91
Q

How do alkenes form addition polymers

A

The double bonds in alkenes can open up and join together to make long chains called polymers

92
Q

What are the small alkenes called in addition polymers

A

Monomers

93
Q

What is an example of addition polymerisation

A

Poly(ethene) is made by the addition polymerisation of ethene

94
Q

How to draw displayed formula of polymers

A

Monomer:

H H
\ /
C = C n
/ \
H H

Polymer:

H H
\ /
-(- C - C -)-
/ \
H H n

Side links shows that both sides are attached to other units
The molecule in brackets is the repeating unit
n represents the number of repeat units

95
Q

How does addition polymerisation occur

A

Alkenes must be heated at a high temperature and high pressure to open up their double bond and polymerise into long chains of repeating units

96
Q

Name and uses of pol(chloroethene)

A

Also known as poly(vinyl chloride) or PVC
Can be used for: pipes, films and sheeting, bottles

97
Q

Uses for poly(propene)

A

Children’s toys, guttering, rope fibres

98
Q

Name and uses for poly(phenylethene)

A

Also called poly(styrene)
Can be used in packing material, insulating food trays and cups

99
Q

Name and uses for poly(tetrafluoroethene)

A

Also called Teflon or PTFE
Can be used as coating for non stick pans, cable insulation

100
Q

How to dispose of polymers

A

Burying
Reusing
Burning

101
Q

How can waste plastics be buried and what should we do about this

A

Landfill is can be used to deal with waste plastics
Because the amount of waste generated is becoming more of a problem, there’s a need to reduce landfill

102
Q

When is landfill used

A

Used when the plastic is difficult to separate from other waste
When the plastic is not in sufficient quantities to make separation financially worthwhile
When the plastic is difficult technically to recycle

103
Q

Why is reusing plastics beneficial for the environment

A

Many plastics are made from non-renewable oil fractions so it’s beneficial to reuse plastics as much as possible

104
Q

Different ways in which plastics can be reused

A

Can be recycled by melting and remoulding (e.g. polypropene)
Some can be cracked into monomers and used as organic feedstock to make more plastics or other chemicals

105
Q

How can plastics be burned

A

Can be burned to produce heat used for electricity (if recycling isn’t possible)
Process must be controlled to reduce toxic gases (e.g. HCl can be produced when burning PVC)

106
Q

How are waste gases from burning plastics controlled or removed

A

Passed through scrubbers which neutralise gases such as HCl by allowing them to react with a base

107
Q

How do biodegradable polymers decompose

A

Organisms can digest them to form water, carbon dioxide and biological compounds

108
Q

What can biodegradable polymers be made from

A

Made from renewable resources such as starch or oil fractions
These are more expensive than non-biodegradable equivalents

109
Q

How to use biodegradable polymers responsibly

A

Do not decompose in landfill as there’s a lack of moisture and oxygen
Must be placed on a compost heap
Must be collected and separated from non-biodegradable plastics

110
Q

Uses of biodegradable polymers

A

Can be used as sheeting to cover plants from frost
Made from polyethene with starch grains embedded in
Starch is broken down by microorganisms and remaining polyethene crumbles into dust

Scientists started to produce photodegradable polymers which decompose when exposed to sunlight

111
Q

What are bioplastics made from

A

Produced from plant starch, cellulose, plant oils and proteins

112
Q

Difference between primary, secondary and tertiary carbocations

A

Primary: positive carbon atom is connected to 1 other carbon atom
Secondary: positive carbon atom is connected to 2 other carbon atoms
Tertiary: positive carbon atom is connected to 3 other carbon atoms

113
Q

How are the major and minor products formed from alkene addition reactions

A

In addition reactions of an unsymmetrical alkene, the major product is formed from the secondary carbocation
E.g. propene + HBr -> 2-bromopropane (major)
Whereas the primary carbocation intermediate goes on to form the minor product
E.g. propene + HBr -> 1-bromopropane (minor)

114
Q

How do the yields between major and minor products compare

A

Yield of major product is much high than yield of minor product

115
Q

How does markownikoff’s rule occur

A

When an unsymmetrical alkene (e.g. propene) reacts with an unsymmetrical molecules (e.g. hydrogen bromide)

116
Q

How are carbocations classified

A

Classified by the number of R groups attached to positive carbon atom
The more R groups attached to the positive carbon atom, the more stable is it
Primary is the least stable, tertiary is the most

117
Q

Why do more R groups make a carbocation more stable

A

Each alkyl group donates and pushes electrons towards positive charge of the carbocation
So the positive charge is spread over the alkyl groups
The more alkyl groups attached to the positively charged carbon atom, the more the charge is spread out
This makes the ion more stable

118
Q

Why are the yields between major and minor product different

A

The major product is the most stable so more molecules form these molecules to achieve the most stable connection

119
Q

What is markownikoff’s rule summarised as

A

The major product from an addition of a hydrogen halide (HX) to an unsymmetrical alkene is the one where the hydrogen adds to the carbon with the most hydrogen already attached

120
Q

Equation for substitution involving haloalkane and ammonia

A

R - X + NH3 -> R - N+H3 + Br-
R - N+H3 + NH3 -> R - NH2 + NH4+

121
Q

Mechanism of nucleophilic substitution from haloalkane to amine

A

Ammonia acts as Nucleophile and donates electrons to partially positive carbon
Heterolytic fission of C - X bond
Ammonia bonds onto carbon chain producing an amine salt with NH3+ at the end
Second ammonia nucleophile causes a hydrogen to split heterolytically and donate electron to N+ so charge is neutral
Hydrogen ion (proton) bonds to ammonia and forms NH4+ as other product

122
Q

Mechanism of haloalkane to nitrile

A

CN- donates electron to carbon in C-X bond
Heterolytic fission of C-X bond
CN joins onto carbon chain and substitutes X

A Level Chemistry (15 decks)

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