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A-level Chemistry > Organic chemistry > Flashcards

Organic chemistry Flashcards

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1
Q

What are aliphatic hydrocarbons?

A

Straight or branched carbon backbone

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2
Q

What are alicyclic hydrocarbons?

A

Carbon atoms in a ring

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3
Q

What are aromatic hydrocarbons?

A

Delocalised ring

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4
Q

What is a general formula?

A

A formula for all members of a homologous series that involves algebra. e.g. alkanes are CnHn+2

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5
Q

What is a displayed formula?

A

A drawing of the molecule

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6
Q

What is a structural formula?

A

A formula that gives the minimum detail for the arrangement of atoms in a molecule. An example would be CH3(CH2)2CH3 for butane

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7
Q

What is an empirical formula?

A

A formula that shows the smallest integer ratio of atoms in the compound (e.g. H2O2 = HO)

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8
Q

How do skeletal formulae work?

A

A zigzag where each corner represents an atom in the carbon backbone

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9
Q

What are structural isomers?

A

Compounds with the same molecular formulae but different structural formulae

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10
Q

What are the three ways structural isomers can happen?

A

Alkyl groups in different places (different carbon backbone)
Functional groups in different places (e.g. primary vs secondary alcohols)
Different functional groups (e.g. aldehydes vs ketones)

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11
Q

What are stereoisomers?

A

Compounds with the same structural and molecular formulae, but with a different arrangement of atoms in space (different displayed formulae). This is usually due to a double bond preventing the atoms from rotating freely

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12
Q

What is homolytic fission?

A

When a covalent bond breaks and each electron goes to a different atom, forming two highly reactive radicals (atoms with an unpaired electron)

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13
Q

What is heterolytic fission?

A

When a covalent bond breaks and both electrons go to the more electronegative part, forming a positive and a negative ion

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14
Q

What does a curly arrow in a diagram represent?

A

The movement of two electrons

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15
Q

What is a sigma bond?

A

A type of covalent bond where electron orbitals of two atoms overlap end-to-end. Sigma bonds are generally stronger than pi bonds because the extent of overlap is maximum. Single bonds consist of a single sigma bond.

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16
Q

What is a pi bond?

A

A type of covalent bond where the lobes (ends) of two electron orbitals overlap. Double bonds consist of a sigma bond and a pi bond.

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17
Q

Describe the bonding in an alkane

A

Alkanes contain sigma bonds (C-H and C-C). C and H have similar electronegativity values, meaning alkanes are non-polar

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18
Q

Why do alkanes’ boiling points increase as the chain length increases?

A

The surface area of contact between molecules increases, increasing the number of induced dipole-dipole forces

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19
Q

Why do branched alkanes have lower boiling points?

A

The surface area of contact between molecules is lower

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20
Q

Why do alkanes have low reactivity with many reagents?

A

All the covalent bonds in alkanes have low electronegativity and high bond enthalpy

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21
Q

What are the types of combustion of alkanes?

A

Complete (producing CO2 and water), and incomplete (producing CO2, water, carbon and carbon monoxide)

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22
Q

Describe the bonding in alkenes

A

Double C=C bonds which contain a sigma and a pi bond. The pi bond restricts rotation around the C=C double bond

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23
Q

Why do alkenes have a trigonal planar shape?

A

Each carbon atom has 3 areas of electron density, the double bond and the two C-H single bonds. The negatively charged areas repel, forming bond angles of 120.

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24
Q

What are electrophiles?

A

Species which accept electron pairs

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25
Q

Why are alkenes more reactive than alkanes?

A

The high density of the C=C bond attracts electrophiles

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26
Q

What is a saturated hydrocarbon?

A

A hydrocarbon with only single bonds, such as an alkane

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27
Q

Why do plastics remain chemically unchanged in the environment for hundreds of years?

A

They are saturated organic compounds, meaning they are very stable

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28
Q

How are plastics disposed of?

A

Landfill, combustion, reusing, recycling, using them as organic feedstock

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29
Q

Describe the combustion of a plastic

A

Since plastics are organic, they can be burnt. Their combustion releases carbon dioxide, which is a greenhouse gas. Depending on the type of plastic, other gases such as HCl can be made, which can be removed using gas scrubbers or a base such as CaO. Plastics can be burnt in power stations to generate heat and produce electricity

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30
Q

Describe the recycling of plastic

A

Plastics are sorted into different types, which is labour intensive. They are then cleaned, melted down and reshaped into new products. These new products are often of worse quality, and only 7% of plastic is recycled

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31
Q

What is a primary alcohol?

A

An alcohol where the oxygen in the -OH group is bonded to a C with only one other C attached

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32
Q

How do you tell if an alcohol is primary, secondary or tertiary?

A

Look at how many carbons are bonded to the carbon bonded to the -OH group (1 = primary etc.)

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33
Q

Why do alcohols’ boiling points increase as the chain length increases?

A

The surface area of contact between molecules increases, increasing the number of induced dipole-dipole forces

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34
Q

Why do alcohols have higher boiling points than their corresponding alkanes?

A

There are hydrogen bonds between molecules, caused by the oxygen atom

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35
Q

What is volatility?

A

The tendency of a substance to evaporate at room temperature

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36
Q

Why are alcohols less volatile than alkanes?

A

Hydrogen bonds

37
Q

Why do alcohols become less soluble as chain length increases?

A

The aliphatic chain cannot form hydrogen bonds

38
Q

What is reflux?

A

Constant boiling and condensing of a reaction mixture. This ensures that the reaction completes as much as possible without losing reactants or products to the air

39
Q

What happens when you try to oxidise a tertiary alcohol?

A

Nothing

40
Q

How are esters named?

A

First part: Name of alkyl chain attached to -OH on alcohol

Second part: Carboxylic acid stem name + “-oate”

41
Q

Describe the reactivity of haloalkanes

A

There is a difference in electronegativity between halogens and carbon, so haloalkanes are polar. The positive carbon atom is attacked by nucleophiles (species with full or partial negative charge which donate electron pairs)

42
Q

Describe nucleophilic substitution of a haloalkane

A

The two unpaired electrons from the nucleophile form a bond with the slightly positively charged carbon atom, breaking the carbon-halogen bond.

43
Q

What is hydrolysis?

A

A type of nucleophilic substitution where water provides the OH- ions which act as nucleophiles.

44
Q

What determines the rate of hydrolysis?

A

The bond enthalpy of the carbon-halogen bond. This decreases as the halogen gets bigger, meaning that iodoalkanes hydrolyse the fastest

45
Q

Describe hydrolysis using aqueous alkali

A

When a haloalkane is heated under reflux with hydroxide ions, an alcohol is made. This reaction is faster than hydrolysis with water

46
Q

What are chlorofluorocarbons?

A

Haloalkanes containing fluorine and carbon. They are inert due to the high bond enthalpies of the C-Cl and C-F bonds. They are used for refrigeration and fighting fires.

47
Q

How do chlorofluorocarbons damage the ozone layer?

A

When the CFCs reach the stratosphere, they are exposed to UV, forming radicals which decompose ozone into oxygen

48
Q

What is the difference between electrophilic substitution and electrophilic addition?

A

Electrophilic substitution involves an atom or group being lost from the molecule

49
Q

Describe electrophilic substitution of benzene

A

Benzene donates an electron to the electrophile, breaking the delocalised ring. An unstable positive ion forms. H+ is lost, and the delocalised ring is reformed

50
Q

What is a halogen carrier?

A

A catalyst that accepts a lone pair of electrons from a halogen atom on an electrophile, increasing the polarisation in the molecule. These include aluminium halides, iron halides and iron

51
Q

NaBH4 reduction reaction mechanism

A

H- ions from the NaBH4 donate an electron pair to the carbon and bond to it. This causes the oxygen to donate one of the electron pairs from the C=O bond to an H+ ion, forming a bond. The end result is that 2 hydrogens are added around the C=O bond. The same thing happens with KCN and acid, except the bottom H is replaced with CN.

52
Q

How can you compare rates of hydrolysis of haloalkanes?

A

Putting silver nitrate solution in the mixture and seeing how long it takes for a precipitate to form and what colour it is

53
Q

[PPQ] How does branching affect the boiling point of a molecule?

A

More branching means less surface contact between molecules, and therefore weaker London forces which require less energy to break

54
Q

Describe the bonding in benzene

A

The p-orbitals of all carbons overlap to create a pi-system (two ring-shaped clouds of electrons, above and below the carbons). Thus all the bonds are the same, and the electrons are delocalised

55
Q

Reaction of phenol with bromine water

A

Occurs because phenol is more reactive than benzene.

Phenol + 3Br2 => Tribromophenol + 3HBr

56
Q

How do amino acids react with alkali?

A

The carboxylic acid group reacts, forming water and a salt

57
Q

How do amino acids react with acids?

A

The amino group reacts and forms a salt of the conjugate acid

58
Q

How do amino acids react with alcohols?

A

In the presence of a strong acid catalyst, an amino acid reacts with an alcohol to form an ester

59
Q

What is a chiral carbon atom?

A

A carbon atom with 4 different groups attached to it, meaning the groups can be arranged in 2 different, non-superimposable ways. These molecules are called enantiomers

60
Q

What happens when a molecule has N chiral centres?

A

It has 2^n optical isomers. If a molecule has 2 chiral centres, the isomers are:

  • The original molecule
  • The original but with one carbon mirrored
  • The original but with the other carbon mirrored
  • The original with both carbons mirrored
61
Q

How do condensation polymers work?

A

The functional group on one monomer reacts with the functional group on another monomer to form a link, eliminating a small molecule (usually H2O or HCl)

62
Q

How can condensation polymers be broken down?

A

Water molecules and H+ are added, and the links are broken (hydrolysis). Polyamides hydrolyse easily with an acid and polyesters hydrolyse easily with a base

63
Q

How do dicarboxylic acids and diamines react?

A

Each molecule forms CONH links with 2 other molecules, releasing water and forming a polyamide

64
Q

How do dicarboxylic acids and diols react?

A

Each molecule forms COOH (ester) links, forming a polyester

65
Q

What is the carbonyl functional group?

A

C=O

66
Q

Reaction of hydrogen cyanide with carbonyl compounds

A

Nucleophilic addition reaction, producing hydroxynitriles

67
Q

How do you test for the presence of a C=O group in aldehydes and ketones?

A

Add 2,4-DNP (Brady’s reagent) dissolved in methanol and concentrated sulfuric acid, and a bright orange precipitate will be formed. This precipitate is a derivative of the compound and has a unique melting point. If you crystallise the precipitate and measure the melting point of the crystals, you can work out the compound

68
Q

How do you use Tollens’ reagent to test for an aldehyde?

A

Tollens’ reagent is a solution of silver nitrate in aqueous ammonia. When heated in a test tube, the aldehyde is oxidised and the silver ions are reduced, forming a silver mirror. This does not happen with ketones because they cannot be oxidised

69
Q

What are acyl chlorides?

A

Like carboxylic acids but with the functional group -COCl instead of -COOH. Their names end in “-oyl chloride” and they’re made by reacting carboxylic acids with thionyl chloride (SOCl2)

70
Q

How do acyl chlorides react with water?

A

Vigorous reaction with cold water, producing a carboxylic acid. All 4 reactions of acyl chloride are nucleophilic addition-elimination reactions

71
Q

How do acyl chlorides react with alcohols?

A

Vigorous reaction at room temperature, producing an ester

72
Q

How do acyl chlorides react with ammonia?

A

Violent reaction at room temperature, producing a primary amide

73
Q

How do acyl chlorides react with amines?

A

Violent reaction at room temperature, producing a secondary amide

74
Q

How do acyl chlorides react with phenol?

A

They produce an ester (e.g. phenyl ethanoate) and hydrochloric acid. This is faster than using carboxylic acids, which react very slowly with phenol

75
Q

What are amines?

A

Organic derivatives of ammonia with the hydrogen atoms replaced by organic groups. Whether the amine is primary, secondary, tertiary or a quaternary ammonium ion depends on how many H atoms have been substituted. Amines are bases because the lone pair of electrons on the nitrogen can accept protons

76
Q

How can amines be made from haloalkanes?

A

By heating a haloalkane with an excess of ammonia dissolved in ethanol. This is unpredictable and will produce a mixture of the 4 types of amine.

77
Q

How are aromatic amines made?

A

Heat a mixture of an aromatic nitro compound, tin, and concentrated hydrochloric acid under reflux, making a salt. Then add sodium hydroxide to get the aromatic amine.

78
Q

What are the reagents for acylation and alkylation?

A

AlX3 + RX

X is a halogen (usually chlorine), and X is whatever you’re adding (CH3 or CH3CO)

79
Q

What are the concerns raised by the use of polymers?

A

Incinerating them produces toxic gases, and if not incinerated they stay in nature for thousands of years

80
Q

How are degradable polymers developed?

A

Polymers with C=O bonds are photodegradable (into CO2 and H2O). Some are also readily degradable by hydrolysis at pH 7

81
Q

Formation of an aliphatic amine

A

Haloalkane + anhydrous ethanol + NH3 => Halide ion + Amine salt
Halide ion + amine salt + OH- => Amine + H2O + Halide ion

82
Q

What is the problem with the reaction between haloalkanes and ammonia?

A

The reactants can react with the products

83
Q

How can you control the major product of the reaction between haloalkanes and ammonia?

A

Excess ammonia means the major product is the primary amine

Excess haloalkane means the major product is the quaternary salt

84
Q

Reduction of nitriles

A 
A reducing agent turns the -C≡N group into -C-NH2
Agents:
anhydrous LiAlH4: 4[H]
anhydrous Na (alcohol): 4[H]
Ni (catalyst): 2H2
85
Q

Preparation of aromatic amines

A

Nitrobenzene + Sn + conc HCl under reflux => Phenylamine

ArNO2 + 6[H] + HCl => ArNH3+ + Cl- + 2H2O
ArNH3+ + Cl- + NaOH => ArNH2 + NaCl + H2O

86
Q

How are solids and liquids separated after a reaction?

A

Solids are normally separated by filtration and liquids are separated by simple, fractional or steam distillation

87
Q

How are solids and liquids purified after a reaction?

A

Liquids are normally purified by distillation and solids are purified by recrystallisation

88
Q

How can the product of a reaction be identified?

A

Melting/boiling points, simple tests, NMR

A-level Chemistry (8 decks)

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