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Synthesis Flashcards

1
Q

What is the term given to breaking bonds

A

Fission

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2
Q

What are the 2 types of fission

A

Homolytic

Heterolytic

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3
Q

Describe homolytic fission

A

Each electron in the sigma bond goes to a different atom

Two neutral species are formed

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4
Q

Where does homolytic fission occur

A

When non-polar covalent bonds are broken

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5
Q

What is the first stage of homolytic fission and how is it triggered

A

Initiation

UV

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6
Q

What do single-headed curly arrows symbolise

A

The movement of a single electron

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7
Q

Why are reactions involving homlytic fission unsuitable for producing organic compounds

A

Compounds will be produced in low yields and are difficult to isolate

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8
Q

Where does heterolytic fission occur

A

When polar covalent bonds are broken

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9
Q

Describe heterolytic fission

A

The more electronegative atom takes both of the electrons to make a positive and a negative ion

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10
Q

Why are heterolytic reactions more suitable for gaining products

A

Far fewer products are formed

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11
Q

What is a nucleophile

A

An electron donor

Negatively charged ion or a neutral molecule that is electron rich

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12
Q

What is an electrophile

A

An electron acceptor

Positively charged ion or neutral molecules that is deficient in electrons

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13
Q

What are aromatic hydrocarbons

A

Subset of hydrocarbons of which the simplest of these is benzene.

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14
Q

What is controversial surrounding the reactivity of benzene

A

It resists addition reactions - rapid decolourisation does not take place when added to bromine.

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15
Q

What type of bonding orbitals surround the carbon atoms in arenes (aromatic hydrocarbons)

A

sp*2 hybrid orbitals

  • three of the half filled sp*2 orbitals form sigma bonds with a hydrogen and the two neighbouring carbons
  • an electron is left occupying a p orbital on each carbon atom - these p orbitals overlap to form a pi molecuar orbital.
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16
Q

What is the total amount of orbitals found in benzene

A

12 sigma bonds

1 pi bond

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17
Q

Describe the 6 electrons that make up benzenes pi bond

A

Delocalised

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18
Q

What accounts for benzenes stability and why doesn’t it undergo addition reactions

A

Its delocalised electrons

Addition reactions would disrupt the electron delocalisation and would reduce its stability

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19
Q

Which reactions can occur on benzene without any disruption to its delocalised electrons

A

Substitution

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20
Q

Which aspect of benzene makes it susceptible to electrophiles

A

The delocalised electrons in the pi molecular orbital

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21
Q

List some electrophilic substitution reactions

A

Alkylation (CH3+)
Chlorination (Cl+)
Nitration (NO2+)
Sulfonation (HOSO2+)

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22
Q

What is the name of the benzene group in an alkane

A

Phenyl group.

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23
Q

What does aromatic mean

A

A system that contains a ring of atoms stabilised by delocalised pi electrons

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24
Q

Define aliphatic

A

molecules with straight or branched chains

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25
Q

Which benzene reactions are involved in dye production

A

Nitration

Alkylation

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26
Q

What can haloalkanes be regarded as

A

An alkane in which one or more hydrogens has been replaced by a halogen

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27
Q

What determines if a haloalkane is primary, secondary or tertiary

A

The number of alkyl groups attached to the carbon atom bearing the halogen atom

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28
Q

What is unique about the carbon atom of a monohaloalkane

A

It is polar since the halogen has a greater electronegativity
This makes the monohaloalkane acts as an electrophile

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29
Q

Why are monohaloalkanes susceptible to attack by nucleophiles

A

The halogen has a greater electronegativity which gives the carbon a slightly positive charge making it an electrophile

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30
Q

How do nucleophiles react with monohaloalkanes

A

The nucleophile donates an electron pair to the carbon atom of the c - x bond (x = the halogen) which forms a covalent bond.
The halogen atom is thrown out as a halide ion.

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31
Q

List some nucleophilic substitutions of monohaloalkanes

A

Monohaloalkanes react with:
Aqueous alkalis to form alcohols
Alcoholic alkoxides to form ethers
Ethanolic cyanide to form nitriles

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32
Q

How are alkoxides formed

A

When an alkali metal is added to an alcohol

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33
Q

How do you name nitriles

A

Prefix includes the amount of carbons of alkane and cyanide parts. eg. ethanenitrile = methane + cyanide

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34
Q

How is a nitrile converted into a carboxylic acid

A

Acid hydrolysis (with water and positive hydrogen ions

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35
Q

Which reaction does a monohaloalkane undergo if heated in reflux with ethanolic potassium (or sodium) hydroxide

A

Elimination

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36
Q

Describe an elimination reaction of a monohaloalkane

A

The halogen and a hydrogen on the adjacent carbon is removed from the alkane so it turns into an alkene - it is eliminated and not replaced

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37
Q

What is an reaction of a monohaloalkane when heated with potassium/sodium hydroxide called

A

Base-induced elimination reaction

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38
Q

What is unique about monohaloalkanes with more than 3 carbons that undergo elimination reactions

A

There is 2 possible products

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39
Q

What are the two different mechanisms by which a monohaloalkane will react under

A

Sn1

Sn2

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40
Q

What is the rate equation of a monohaloalkane undergoing Sn1 mechanism

A

Rate = k[(CH3)3CBr]

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41
Q

What is the meaning of Sn1

A

The reaction involves substitution by a nucleophile and that it follows first order kinetics (only one species is involved in the rate-determining step)

42
Q

Describe the first step of the Sn1 process

A

Involves the slow-rate determining step and shows the C-Br bond undergo heterolytic fission to form a carbocation intermediate

43
Q

Describe the second step of the Sn1 process

A

The fast step which involves the nucleophilic attack on the carbocation by the hydroxide ion

44
Q

What is the rate equation of a monohaloalkane undergoing Sn2 mechanism

A

Rate = k[CH3CH2Br][OH-]

45
Q

What is the meaning of Sn2

A

The reaction involves substitution by a nucleophile and that it follows second order kinetics (there are two species involved in the rate determining step)

46
Q

What is the middle state of the Sn2 mechanism called

A

Transition state

47
Q

What arrangement does the species in the transition state of an Sn2 mechanism adopt

A

trigonal bipyramidal

48
Q

What types of carbocation can undergo the Sn1 mechanism

A

Primary, secondary, tertiary

49
Q

What effect does alkyl groups have on the carbocation

A

A positive inducting effect

50
Q

Describe the inductive effect

A

The alkyl groups are electron donating and can push electrons onto the positively charged carbon atom which stabilises the carbocation.

51
Q

Which type of carbocation is the most likely to react with a nucleophile via an Sn1 mechanism and why

A

Tertiary because they are the most stable

52
Q

What effect is associated with the size of the alkyl groups on a carbocation

A

Steric hindrance

53
Q

Why are tertiary carbocations less likely to react with a nucleophile via an Sn2 pathway

A

The nucleophile is sterically hindered as the three bulky Sn2 groups limits the access to the carbocation

54
Q

Which type of carbocation is most likely to react with a nucleophile via an Sn2 mechanism and why

A

Primary - there is only one alkyl group attached to the carbocation so access to the positively charged carbon will be much easier

55
Q

What is the pathway a primary haloalkane is most likely to react via

A

Sn2

56
Q

Why do alcohols have higher boiling points than most other molecules with similar amounts of electrons and similar shape

A

The polar OH- group forms hydrogen bonds with other molecules so require more energy to separate them

57
Q

How does carbon chain length of an alcohol affect its solubility

A

The longer the carbon chain, the less soluble the alcohol (more non-polar and its more difficult for hydrogen bonds so they have a weaker effect)

58
Q

List the ways of how alcohols can be made

A

By heating monohaloalkanes under reflux with aqueous potassium/sodium hydroxide (nucleophilic substitution)

Alkenes in the presence of water with a sulfuric acid catalyst (acid catalysed addition or hydration)

Aldehydes/ketones by reaction with lithium aluminium hydride dissolved in an ether

59
Q

List the possible reactions of an alcohol

A

Alcohols react with:
Reactive metals such as sodium/potassium to form alkoxides (displacement/redox)

Aluminium oxide/concentrated sulfuric acid/concentrated phosphoric acid to form alkenes (dehydration/elimination)

Carboxylic acids/acid chlorides to form esters using a concentrated sulfuric acid catalyst [(condensation/esterification)(acid chloride is way faster and doesn’t require a catalyst)

60
Q

What is the general structure of an ether

A

R-O-R’ where R and R’ are alkyl groups

61
Q

What is the functional group of an ether

A

The alkoxy group

62
Q

How do you name ethers

A

The shorter chain has ‘yl’ placed at the end of it eg. ‘methoxy’
The other alkyl group is placed after it
The number of the carbon on the larger alkyl group that the alkoxy group is attached to is placed in front of the name

63
Q

What is the boiling point of ethers compared to alcohols and why

A

Lower - no hydrogen bonding between other ether molecules (the oxygen atom is not directly bonded to a hydrogen atom)

64
Q

What explains the reason why ethers low in mass are soluble in water

A

They are able to form hydrogen bonds

65
Q

What does it mean when large ethers are insoluble in water

A

They can be useful for extracting organic compounds from aqueous reaction mixtures

66
Q

How flammable are ethers

A

Highly

67
Q

Why do ethers make good solvents

A

Relatively inert chemically and most organic compounds dissolve them
Easily removed by distillation since they are volatile

68
Q

How can you prepare an ether

A

Heating a haloalkane under reflux with an alkoxide (nucleophilic substitution)

69
Q

Describe how alkenes can be prepared

A

Dehydration of alcohols - the vapour can be passed over hot aluminium oxide/alcohol can be treated with concentrated sulfuric acid/concentrated phosphoric acid

Base-induced elimination of hydrogen halides from monohaloalkanes - heating monohaloalkanes under reflux with ethanolic potassium/sodium hydroxide

70
Q

Describe the process of dehydration

A

The OH- group is removed as well as a H on the adjacent carbon

71
Q

What is another name for dehydration

A

Elimination

72
Q

Why is concentrated phosphoric acid preferred over concentrated sulfuric acid when dehydrating alcohols

A

Sulfuric acid leads to more side reactions and may lead to charring

73
Q

List the possible addition reaction paths of alkenes

A

React with:
Hydrogen to form alkanes (hydrogenation)(catalysed by nickel/platinum)
Halogens to to form dihaloalkanes (halogenation)
Hydrogen halides to form monohaloalkanes (hydrohalogenation)
Water to form alcohols (hydration)(catalysed by acids)

74
Q

What is Markovnikov’s rule

A

The major product is the one in which the H atom ends up attached to the carbon atom of the double bond that has a greater number of hydrogens bonded to it.

75
Q

Describe step 1 of halogenation

A

Bromine approaches the double bond and becomes polarised, electrons move to the bromine away from the double bond.
The positive halogen attacks the double bond and a cyclic intermediate is formed along with a negative halogen ion.
The halogen is acting as an electrophile and the double bonded molecule is the nucleophile

76
Q

Describe step 2 of halogenation

A

The negative halogen ion attacks the cyclic intermediate ion on the opposite side.
The negative halogen ion is acting as the nucleophile and the cyclic intermediate ion is the electrophile

77
Q

Describe step 1 of hydrohalogenation

A

The H-Br molecule is already polarised.
The positive H attacks the double bond forming an intermediate carbocation.
The H-Br molecule breaks heterolytically creating a negative Br ion.

78
Q

Describe step 2 of hydrohalogenation

A

Involves the nucleophilic attack of the Br ion on the carbocation from either side.
If the molecule is unsymmetrical, the molecule with more alkyl groups attached to the carbocation will be more stable because of the positive inductive effect.

79
Q

Describe step 1 of acid-catalysed hydration

A

A positive hydrogen ion bonds with a double bond which makes the alkenes carbon a carbocation

80
Q

Describe step 2 of acid-catalysed hydration

A

The carbocation undergoes nucleophilic attack by a water molecule which makes a protonated alcohol

81
Q

what is a protonated alcohol

A

An alcohol with an extra hydrogen on the OH group (a proton is a positive hydrogen)

82
Q

Describe step 3 of acid-catalysed hydration

A

The protonated alcohol is a strong acid and readily loses a proton (hydrogen ion)

83
Q

How can you prepare a carboxylic acid

A

Carboxylic acids can be prepared by:
Oxidising primary alcohols or aldehydes (heating under reflux with acidified potassium dichromate solution)

Hydrolysing nitriles (heated under reflux with an aqueous acid)

Hydrolysing esters (heated under reflux with an aqueous acid/alkali as a catalyst)

Hydrolysing amides (heating under reflux with an aqueous acid/alkali)

84
Q

What reacts with a carboxylic acid to make salts

A

Metals
Carbonates
Alkalis

85
Q

What do carboxylic acids react with (where no salt end product is formed)

A

Amines to form alkylammonium salts which form amides upon heating
Lithium aluminium hydride (LiAlH4) in ether to form primary alcohols (reduction)

86
Q

What are amines

A

Organic derivatives of ammonia in which one or more hydrogen atoms in ammonia has been replaced by alkyl groups

87
Q

How do you name amines

A

Usually put ‘amine’ after eg. methylamine 🙃
If the amide group is attached to a carbon in the middle of the chain: example = 2 aminopropane
Use for instance ‘ethyl

88
Q

How do you name secondary/tertiary amines

A

Use prefixes ‘di’ and ‘tri’ respectively

89
Q

Why do primary and secondary amines have hydrogen bonding

A

The N-H bond is polar

90
Q

Why do tertiary amines not have hydrogen bonding with other tertiary amines

A

There is not a hydrogen directly connected to the nitrogen

91
Q

Why do primary and secondary amines have higher boiling points than isomeric tertiary amines

A

They contain hydrogen bonds

92
Q

Why are amines with low mass soluble in water

A

They can form hydrogen bonds with waters OH groups

93
Q

How is an amine a weak base

A

The lone pair of electrons on the nitrogen accepts a proton from the water generating alkyammonium ions and hydroxide ions. The OH makes the solution alkali.

94
Q

What do amines react with

A

Mineral acids to form salts

Carboxylic acids to form salts

95
Q

What are the reagents and electrophiles in alkylation

A

R - CH3Cl/AlCl3

E - CH3+

96
Q

What are the reagents and electrophiles in chlorination

A

R - Cl2/FeCl3

E - Cl+

97
Q

What are the reagents and electrophiles in sulfonation

A

R - conc. H2SO4

E - HOSO2+

98
Q

What are the reagents and electrophiles in nitration

A

R - conc. HNO3/H2SO4

E - NO2+

99
Q

What is the name of new organic molecules which chemists are trying to make

A

Target molecules

100
Q

List organic reactions

A 
Substitution
Addition
Elimination
Condensation
Hydrolysis
Oxidation
Reduction
101
Q

What is a functional group

A

The reactive part of a molecule which is responsible for the molecules reactions

102
Q

How can you increase the chain length of a hydrocarbon

A

Adding a cyano group making it nitrile

Advanced higher chemistry (3 decks)

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