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MECH U3/4 > Organic chem > Flashcards

Organic chem Flashcards

1
Q

Why do carbon atoms form strong covalent bonds with other carbon atoms?

A

Due to the relatively small size of the carbon atom and the high valency of carbon (4 electrons)

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2
Q

What are 3 types of hydrocarbons?

A

Aromatics
Aliphatic
Cycloalkanes

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3
Q

What does the ring in the benzene structure represent?

A

Show the double bond that is spread out around the ring of carbon atoms, making a cloud of delocalised electrons above and below the ring, making it stable.

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4
Q

What are functional groups?

A

Most organic compounds are derivatives of hydrocarbons that have one or more hydrogen atoms replaced by other atoms or groups of atoms.

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5
Q

Order from least important to most important functional group. (11)

A 
Alkyl groups
Alkyl halides
Alkynes
Alkenes
Cyclic compounds
Primary amines
Alcohols
Ketones
Aldehydes
Carboxylic acids
Esters
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6
Q

What are primary amines?

A

Amines are homologous series of organic compounds that contain amino functional group.

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7
Q

Why is CH₃CH₂CH₂OH < CH₃CH₂OCH₃ < CH₃CH₂CH₂CH₃ in reference to the increasing boiling points.

A

Dispersion forces between the molecules of the three compounds will be of similar strength because they all have similar number of electrons.

In butane, there are only dispersion forces, in methoxyethane there are both dispersion forces and dipole-dipole forces so boiling point will be higher than butane. Propan-1-ol has both dispersion forces and relatively strong hydrogen bonds and so has the highest boiling point

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8
Q

How does solubility occur?

A

Solubility in water relates to the ability of three substances to form bonds with water that compensate for the hydrogen bonds that have to be broken between water molecules in the dissolving process.

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9
Q

Why is CH₃CH₂CH₂OH < CH₃CH₂OCH₃ < CH₃CH₂CH₂CH₃ in reference to the increasing solubility.

A

It is not possible for butane to form anything other than dispersion forces with water, as so doesn’t dissolve in water. Methoxyethane will be slightly more soluble than butane as dipole-dipole forces and dispersion forces together may allow a few molecules to dissolve. Propan-1-ol is able to form hydrogen bonds to water molecules and so it is much more soluble.

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10
Q

What is an amino functional group consist of?

A

NH2

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11
Q

How do name an amine, suffix and if there is more important functional group?

A
  • replace ‘e’ at the end of the parent alkane’s name with the suffix ‘-amine’
  • If there is a more important functional group the amine is named as ‘amino-‘
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12
Q

What is the functional group of an alcohol?

A

-OH

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13
Q

How do name an alcohol, suffix and if there is more important functional group?

A
  • remove ‘e’ from end and add suffix ‘-ol’

- - If there is a more important functional group the amine is named as ‘hydroxyl-‘

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14
Q

At what angle are bonds between carbonyl functional groups?

A

120º

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15
Q

What is the carbonyl group of a ketone?

A

-CO-

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16
Q

How do name an ketone, suffix and if there is more important functional group?

A

‘-one’

carbonyl

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17
Q

What is the carbonyl group of a Aldehyde?

A

-CHO-

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18
Q

How do name an aldehyde, suffix and if there is more important functional group?

A

‘-al’

carbonyl

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19
Q

What is the carbonyl group of a carboxylic acid?

A

-COOH

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20
Q

How do name an carboxylic acid, suffix and if there is more important functional group?

A

-oic acid

carboxyl

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21
Q

What is the carbonyl group of a ester?

A

-COO-

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22
Q

How do name an ester suffix and if there is more important functional group?

A

‘-yl’ ‘-oate’

Ester

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23
Q

For alkanes and alkenes, boiling points increase

A

as the size of the alkane molecule increases

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24
Q

Why are boiling points of alkanes considerably low?

A
  • as alkanes are non-polar, only intermolecular forces of attraction between them are weak dispersion forces.
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25
Q

Why do boiling points increase as the length of the molecule increases?

A

length of carbon chain increases the overall forces of attraction between molecules increase because of increased strength of temporary dipoles within molecule

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26
Q

Why do straight chain alkanes have higher boiling points than branched chain isomers?

A

Straight chain alkanes fit together more closely and so have higher boiling points than branched-chain isomers, with are unable to come as close together in the bulk substance.

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27
Q

Why are boiling points of alkenes relatively low?

A

non-polar and the forces of attraction between them are only weak dispersion forces

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28
Q

Why do the boiling points of alkenes increase with molecular size?

A

as the strength of dispersion forces between molecules increases.

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29
Q

Are alkanes and alkenes soluble in water? And why?

A

No as they are non-polar
and weak dispersion forces between water molecules and hydrocarbon molecules are not strong enough to overcome the strong attraction between water molecules, so two substances remain separate and do not mix. (immiscible)

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30
Q

Are alkanes soluble in organic solvents? And why?

A

alkanes mix with other non-polar liquids, such as alkenes and symmetrical haloalkanes.
as forces of attraction between molecules of these liquids are also weak dispersion forces and of similar strength to the alkane-alkane forces of attraction, they are miscible

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31
Q

Why are boiling points of alcohols high?

A

due to presence of hydrogen bonds between neighbouring alcohol molecules.
The -OH is a polar bond as oxygen is more electronegative atom than hydrogen and so it strengthens the intermolecular bonding

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32
Q

What increases the boiling points of alcohols, amines, amides and carboxylic acids?

A

as molar mass increase

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33
Q

Why does alcohol increase in boiling point with increase in molar mass

A

as length of hydrocarbon chain increases from one member of the homologous series to the next the molar mass increases. Increase in molecular size, dispersion forces between molecules also become stronger.

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34
Q

How does the 3D structure of molecules can also affect boiling points of alcohol?

A

The position of the hydroxyl group within the molecule affects the hydrogen bonding. Boiling points of alcohols decrease in the sequence from primary to secondary to tertiary alcohols as hydroxyl group become increasing ‘crowded’, the presence of the alkyl groups restricts a molecules ability to form hydrogen bonds with other molecules.

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35
Q

What are two things that affect the boiling point of alcohols?

A

Molar mass

3D structure

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36
Q

Which of the three alcohols has the highest boiling points?

A

Primary>secondary>tertiary

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37
Q

Why amines and amides have relatively high boiling points?

A

highly polar nitrogen-hydrogen bonds in amine and amide molecules means that these molecules can form hydrogen bonds.

38
Q

How are the hydrogen bonds created in amines?

A

hydrogen bonds form between non-bonding pair of electrons on the electronegative nitrogen atom and partially positive hydrogen atom on another amine molecule.

39
Q

How are hydrogen bonds created in amides?

A

hydrogen bonds form between non-bonding electron pairs on the oxygen atoms of one molecule and the partially positive hydrogen atom on a neighbouring molecule.

40
Q

How do hydrogen bonds form between carboxylic acids?

A

Two molecules of carboxylic acid in liquid state can form a stable species with a molar mass that is double that of a single carboxylic acid molecule, two hydrogen bonds form between the molecules.

41
Q

Why are boiling points high in carboxylic acids?

A

Increase in size from the formation of a dimer increases the strength of dispersion forces between one dimer and its neighbours, therefore a higher boiling point observed

42
Q

Are alcohols, amides, amines and carboxylic acids soluble in water?

A

They are only soluble in water when they have short carbon chains

43
Q

Why are alcohols, amides, amines and carboxylic acids soluble in water?

A

as hydrogen bonds can form between polar functional groups and adjacent water molecules.

44
Q

Why are alcohols soluble in water? (3)

A
  • hydrogen bonds form between partially positive hydrogen atom of ‘-OH’ group and lone-pair electrons on the alcohol.
  • also attraction between partially positive hydrogen within the water molecules and the lone-pair electrons on the alcohol.
  • ‘-OH’ of an alcohol can form bonds with water molecules but the hydrocarbon tail cannot.
45
Q

Why are amines soluble in water?

A

hydrogen bonds can form between the lone-pair electrons of nitrogen and the partial positive hydrogen of an adjacent water molecule or between the hydrogen of an amine group and an oxygen of an adjacent water molecule

46
Q

Why is carboxylic acid soluble in water?

A

When carboxylic acids dissolve in water, hydrogen bonding occurs between water molecules and both the C=O group and the —OH group, more soluble than alcohols in water

47
Q

Why do longer chains not dissolve well in water?

A

The longer hydrocarbon chains disrupt the hydrogen bonds between water molecules.
Only dispersion forces occur between hydrocarbon chain and water molecules, which are not as strong as hydrogen bond, opposing the tendency for a molecule to dissolve.
As chain length increases, the non-polar nature of the molecule also increases and the alcohol becomes less soluble

48
Q

Are alcohols soluble in organic solvents?

A

Only relatively non-polar alcohols with long hydrocarbon chains dissolve well in non-polar solvents

49
Q

What does not dissolve well in organic solvents?

A

Small alcohols such as ethanol (and also solubilities of amines, amides and carboxylic acids in organic solvents show similar trends) , very soluble in water but does not dissolve well in organic solvents.

50
Q

What makes alcohols become more soluble in organic solvents?

A

Alcohols become more soluble in organic solvents as they get larger.

51
Q

Why do short chain hydrocarbons with functional groups not dissolve well in organic solvents?

A

Dispersion forces between hydrocarbon chains and solvent are not strong enough to disrupt the hydrogen bonds that hold the alcohol molecule together. Alcohol molecules do not separate and disperse throughout the solvent.

52
Q

What are small alcohols used as?

A

Fuels

53
Q

What are some examples of carboxylic acid? (4)

A
  • organic acids found in nature, sour taste to lemon juice and vinegar, or making an ant bite sting
  • Carboxylic acids are weak acids, when food goes bad carboxylic acids can be formed.
  • eg. ethanoic acid is produced when wine is left open to oxygen in atmosphere. It changes into vinegar.
54
Q

Are carboxylic acid’s functional group polar or non-polar?

A

Both groups are polar, oxygen being more electronegative than carbon and hydrogen
electrons are drawn away from hydrogen atom, enabling it to react with water to form an H⁺ ion, acts like an acid

55
Q

Why can’t aldehydes, ketones and esters form hydrogen bonds with each other?

A

They do not have a hydrogen atom bonded to an oxygen atom or a nitrogen atom in their molecules.

56
Q

Do aldehydes, ketones and esters have high or low boiling points? Do they have higher boiling points than similar sized alcohols?

A

High boiling points, but not as high as similar-sized alcohols because of dipole-dipole bonds are not as strong as hydrogen bonds.

57
Q

Why do aldehydes, ketones and esters have high boiling points?

A

all contain a carbon-oxygen double bonds.
Oxygen is much more electronegative than carbon so it is polar, and so there is a permanent dipole, which can form dipole-dipole attractions with nearby molecules.

58
Q

As aldehydes, ketones and esters chains increase, what happens to the boiling points?

A

their boiling points increase as the strength of dispersion forces between molecules also increase.

59
Q

Can aldehydes, ketones and esters form hydrogen bonds between water molecules?

A

Only in small aldehydes, ketones and esters, hydrogen bonds can form between a lone pair of electrons on the oxygen atom of carbonyl group and the partially positive hydrogen atoms in water molecules.

60
Q

Are aldehydes, ketones and esters soluble in organic soluble?

A

when the non-polar hydrocarbon chain length of aldehydes, ketones and esters increases, their solubility in water decreases.

61
Q

What are esters?

A

sweet, fruity odours occurring naturally in fruits and flowers, found in perfume or aftershave

62
Q

Are esters polar or non-polar?

A

polar, they have no free hydroxyl groups, so they cannot form hydrogen bonds with each other. Therefore have lower boiling points than carboxylic acids and alcohols of similar relative molecular mass

63
Q

Why are small esters good solvents for organic compounds?

A

As they dissolve well in organic substances and their polar nature

64
Q

What are small esters used for?

A

Butyl ethanoate is used as paint thinner and ethyl ethanoate is found in nail polish removers.

65
Q

What are large esters used for?

A

exist as oils or waxes,

like beeswax

66
Q

Explain why carbon chains in alkanes are not straight, as commonly drawn in structural formulae

A

Carbon atoms in hydrocarbons have four bonds to other atoms. According to valence shell electron repulsion theory, the angle around between each bond is 109.5º and the geometry around each carbon is tetrahedral. This means that carbon-carbon bonds are much less than 180º and so the chain is zig-zag shaped.

67
Q

What catalyst is used for addition reactions with hydrogen?

A

metal catalyst such as nickel

68
Q

What catalyst is used for addition reactions with halogens?

A

no catalyst as it proceeds at room temperature

69
Q

What can be used as a strong inorganic oxidising agents?

A

acidic solutions of potassium dichromate (K₂Cr₂O₇) and potassium permanganate (KMnO₄)

70
Q

What happens to primary alcohols when they are oxidised?

A

First stage, primary alcohol are oxidised to an aldehyde.

In the second stage, further heating of the reaction mixture in the presence of oxidising agent oxidises the aldehyde to a carboxylic acid.

71
Q

What happens to secondary alcohols when they are oxidised?

A

they oxidise to form ketones

72
Q

What happens to tertiary alcohols when they are oxidised?

A

They are not oxidised.

During oxidation of alcohols, there is an increase in number of C-O bonds and simultaneous decrease (at the same carbon atom) in the number of C-H bonds.
In tertiary alcohols, carbon attached to hydroxyl group does not have a C-H bond to break and so oxidation cannot occur at that carbon atom.

73
Q

What colour changes occur in oxidation when using potassium dichromate?

A

dichromate ions in water is orange

when acidified dichromate solution is reduced to chromium ion (Cr³⁺) which is green

74
Q

What colour changes occur in oxidation when using potassium permanganate?

A

is a deep purple colour

when it reacts MnO₄⁻ is reduced to Mn²⁺ which is a very, very pale pink and appears colourless.

75
Q

What happens when carboxylic acids react with metal oxides and hydroxides?

A

They form metal salts and water

76
Q

What happens when carboxylic acids react with metal carbonates and hydrogen carbonates?

A

A salt, water and carbon dioxide

77
Q

What happens when carboxylic acids react with reactive metals?

A

salt and hydrogen gas

78
Q

What happens when carboxylic acid reacts with alcohol?

A

Esterification reaction occurs where carboxylic acid and alcohol make an ester and water

79
Q

What is the reverse condensation reaction between carboxylic acids and alcohols? What is it catalysed with?

A

Hydrolysis of esters

80
Q

What is it catalysed with?What happens when a catalyst is used for the hydrolysis of esters?

A
  • is catalysed by an alkali or dilute acid
  • when it is catalysed by an alkali such as sodium salt, the products are alcohol and sodium of salt of the carboxylic acid. Sodium salt can be easily converted to carboxylic acid by adding dilute acid solution, such as HCl
81
Q

What is the reaction called between an Alkene and hydrogen?

A

Addition (hydrogenation)

82
Q

What is the reaction called between an alkene and water (with a catalyst and heat)

A

Addition (hydration)

83
Q

What is the reaction called between an alkene in the presence of a catalyst? And what are the products

A

Addition polymerisation

Saturated hydrocarbon polymer

84
Q

Why is sulfuric acid used in reactions of the oxidation of alcohols and in the esterfication reaction?

A

In the redox reaction of alcohols with permanganate and dichromate, hydrogen ions are needed as a reactant. The sulfuric acid added to the permanganate and dichromate solutions is the source of hydrogen ions.

In the condensation reaction of an alcohol with carboxylic acid, the sulfuric acid acts as a catalyst increasing the rate of reaction.

85
Q

Why can’t a carboxylic acid functional group attached to an alcohol not oxidise?

A

During the oxidation of alcohols by dichromate, There is an increase in number of C-O bonds and simultaneous decrease (at the same carbon atom) in the number of C-H bonds.
Like the tertiary alcohols, the carboxylic acid C atom in tertiary alcohols cannot be oxidised by dichromate.

86
Q

Why will ethanol condense but not ethene by cooling them?

A

Cooling condenses only the thanks because it has a lower boiling point than ethene. Ethanol has hydrogen bonding and dispersion forces as its intermolecular forces, while non-polar ethene has only dispersion forces as its intermolecular force.

87
Q

Why do alcohols have higher boiling point than their corresponding Alkane?

A

Alcohols contain a hydroxyl group so hydrogen bonds can form between alcohol molecules.

88
Q

What is produced when an alcohol or carboxylic acid reacts with sodium?

A

Sodium ‘-oxide’ and H2 gas

89
Q

What reacts with sodium?

A

Alcohols and carboxylic acids

90
Q

What is one similarity between pentane, pentanal and pentanoic acid when it comes to boiling point?

A

-they all have similar dispersion forces due to their size/structure

91
Q

Why was the experiment carried out in the absence of UV light?

A

To ensure that substitution reactions do not occur

MECH U3/4 (8 decks)

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