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Chemistry > Unit 3: Section 5 - Isomerism and Carbonyl Compounds > Flashcards

Unit 3: Section 5 - Isomerism and Carbonyl Compounds Flashcards

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1
Q

What property must a carbon atom have for the molecule to display optical isomerism about that carbon atom?

A

4 different substituents attached to 1 carbon atom

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2
Q

What are the similarities and differences between 2 optical isomers?

A

Same atoms and bonds, but they are non-superimposable mirror images of one another, NOT ALWAYS IDENTICAL in chemical properties
Differ int jhe way they rotate plane polarised light - rotate plane of polarisation by the same angle but in different directions

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3
Q

What word is used to describe optically active molecules?

A

Chiral

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4
Q

What are the pair of isomers called?

A

Enantiomers

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5
Q

What is the chiral centre?

A

The carbon that has 4 different substituents attached to it

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6
Q

How is the chiral centre denoted?

A

C*

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7
Q

Give 2 examples of chiral molecules

A
  1. All alpha amino acids, excpet glycerine
  2. Lactic acid / 2-hydroxyporpanoic acid
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8
Q

How is light polarised?

A

By passing it through a polaroid filter, so oscillations are only in 1 plane

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9
Q

What effect does the racemic mixture have on plane polarised light?

A

None, as the rotation by each enantiomer cancels out

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10
Q

What effect does the + isomer have on plane polarised light?

A

Rotates plane of polarisation clockwise

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11
Q

What effect does the - isomer have on plane polarised light?

A

Rotates plane of polarisation anti-clockwise

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12
Q

What is the structure of a polarimeter?

A
  1. Light source (unpolarised light)
  2. Polarising filter (polarised light)
  3. Polarised light passes through compartment containing sample
  4. Detector determines the angle of rotation of the plane polarised light
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13
Q

What are polarimeters used for?

A

To identify which enantiomer is present, the purity of the sample, the concentration of the sample

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14
Q

What is the first stage of the synthesis of lactic acid (2-hydorxypopanoic acid) from ethanal? And the equation?

A

Reagents: KCN and HCl
CH3CHO + HCN -> CH3CH(OH)CN

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15
Q

Why is the CH3CH(OH)CN molecule formed chiral?

A

H, CH3, OH and CN groups attached to the central chiral carbon atoms - 4 substituents

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16
Q

What is the second stage of the synthesis of lactic acid (2-hydroxypropanoic acid) from ethanal?

A

Hydrolysis: CH3CH(OH)CN + HCl + 2H2O -> CH3CH(OH)COOH + NH4Cl

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17
Q

How does the 2nd stage synthesis of lactic acid (2-hydroxypropanoic acid) from ethanal affect the chirality?

A

Doesn’t affect it - still racemic as chirality is not affected by this stage

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18
Q

Are racemic mixtures formed in nature? Why?

A

Not often, as enzyme mechanisms are 3D so only form 1 enantiomer

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19
Q

Why is optical isomerism a problem for the drug industry?

A

Sometimes, only 1 enantiomer is effective due to enzyme’s active site/cell receptors being 3D

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20
Q

What are the options to resolve the issue of only 1 enantiomer being effective?

A
  1. Separate enantiomers - difficult and expensive as have very similar properties
  2. Sell racemate - wasteful as half is inactive
  3. Desing alternative synthesis to only produce 1 enantiomer
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21
Q

What are some examples of optically active drugs?

A

Ibruprofen, Thalidomide

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22
Q

Why is ibruprofen able to be sold as a racemate, even thought the + isomer is needed to treat inflammation?

A
  • Sold as a 50% racemate
  • The body converts 60% of R- isomer to S+ isomer
  • End up with 80% S+ isomer
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23
Q

What is the carbonyl group?

A

C=O

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24
Q

What is the functional group and general formula for an aldehyde?

A

RCHO (C double bonded to O, single bond to H and R)

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25
Q

What is the functional group for a ketone?

A

RCOR (C=O)

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26
Q

How do you name aldehydes?

A

-al suffix (C=O) is on the end of a chain

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27
Q

How do you name ketones?

A

-one suffic (designate number for which carbon C=O is on)

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28
Q

What kind of intermolecular forces do molecules with the carbonyl group have? Why?

A

Permanent dipole-dipole due to the polra C=O bond (O is delta -)

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29
Q

Are carbonyl compounds soluble in water? Why?

A

Yes - form hydrogen bonds between water molecules and oxygen of C=O
As C chain length increases, solubility decreases

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30
Q

Which bond in carbonyl compounds is usually involved in reactions? Why?

A

C=O due to the polarity of the bond (large difference in electronegativity between C and O)

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31
Q

What is the strongest bond in carbonyl compounds?

A

C=O

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32
Q

What mechanism do carbonyl compounds usually undergo?

A

Nucleophilic substitution

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33
Q

Why is the addition of HCN to carbonyl compounds important?

A

Increases the length of the carbon chain by one carbon atom - very useful

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34
Q

Will the product of HCN added to a carbonyl compound have optical isomers? Why?

A

Yes
* In the aldehyde/ketone, the carbonyl carbon is planar
* Equal probability :CN- can attack from either above or below, forming 2 enantiomers

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35
Q

What is the name of the product when HCN is added to a carbonyl compound?

A

Hydroxynitriles

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36
Q

What is Fehling’s solution? What colour is it?

A

Copper complex ions - blue

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37
Q

What happens when an aldehyde is added to Fehling’s solution?

A

Reduced to CU+ ions -> colour change to brick red ppt

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38
Q

What happens when a ketone is added to Fehling’s solution?

A

No visible change - stays blue

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39
Q

What is in Tollen’s reagent?

A

Silver complex ions - colourless solution

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40
Q

What happens when an aldehyde is added to Tollen’s reagent?

A

Silver mirror forms as Ag+ reduced to Ag(s)

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41
Q

What happens when a ketone is added to Tollen’s reagent?

A

No visible change

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42
Q

What is another oxidising agent for alcohols and aldehydes? What change in colour does this undergo?

A

Acidified potassium dichrmate (VI) -H2SO4 and K2Cr2O7
Colour change from orange to green

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43
Q

What is a reducing agent for aldehydes and ketones? What ions does this release in solution?

A

NaBH4 (sodium tetrahydridoborate (III))
Releases an H- ion

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44
Q

What is the mechanism for the reduction of an aldehyde?

A

Nucleophilic addition

45
Q

What is the equation for the reduction of pentan-2-one and for 3-methylbutanal?

A
  • CH3COCH2CH2CH3 + 2[H] -> CH3CH(OH)CH2CH2CH3
  • CH3CH2CH2(CH3)CHO + 2[H] -> CH3CH2CH2(CH3)CH2OH
46
Q

What is a carboxylix? Functional group?

A

-COOH (C=O and C-OH)

47
Q

How do you name carboxylic acids?

A

-oic acid

48
Q

Are carboxylic acids soluble in water? Why?

A

Yes - acid groups can form hydrogen bonds with water molecules

49
Q

What are the intermolecular forces in carboxylic acids?

A

Hydrogen bonds in solid state - very strong

50
Q

What are esters (what are they formed from)? Functional group, general formula?

A

Formed from carboxylic acids and alcohols
RCOOR (C=O, C-O-C)

51
Q

What is the equation for the reaction of ethanoic acid with propan-1-ol?

A

CH3COOH + CH3CH2CH2OH -> CH3COOCH2CH2CH3 + H2O

52
Q

How do you name esters?

A

Start with the group that has replaced the hydrogen (alcohol usually), then the acid part

53
Q

What characterisitc physical properties do esters have?

A

Volatile, pleasant fruity smells

54
Q

What are some uses of esters?

A

Flavourings, perfumes (both for longer chains), solvents (short chains), plasticisers

55
Q
A
56
Q

What are some common natural esters?

A

Fats and oils

57
Q

Is the carboxylic acid group polarised?

A

Yes

58
Q

What is the equation for the equilibrium formed by an ethanoic acid in solution?

A

CH3COOH (aq) ⇌ CH3COO- (aq) + H+ (aq)

59
Q

What happens to the negative charge on the ethanoate ion in terms of electrons?

A

Electrons delocalise so the negative charge is shared across the whole of the carboxylate group

60
Q

How could you distinguish carboxylic acids from other -OH containing compounds?

A

Add NaHCO3
Acids will produce sodium salt, water and carbon dioxide

61
Q

What is the equation for the reaction of ethanoic acid with NaOH?

A

Ch3COOH + NaOH -> H2O + CH3COO-Na+

62
Q

What is the equation for the reaction of ethanoic acid with Na2CO3?

A

2CH3COOH + Na2CO3 -> 2CH3COO-Na+ + H2O + CO2

63
Q
A
64
Q

What catalyst is needed for the formation of esters from alcohols and carboxylic acids?

A

Concentrated strong acid (H2SO4)

65
Q

What catalyst is needed for the hydrolysis of esters?

A

Dilute strong acid (H2SO4)

66
Q
A
67
Q

What is an alternatice method of hydrolysis?

A

Base hydrolysis

68
Q

What are the advantages of base hydrolysis?

A

Reaction goes to completion due to neutralisation by base - more product in the mixture than acid catalysed hydrolysis

69
Q

Which alcohol forms the esters that make up animal and vegetable oils?

A

Glycerol - propane-1,2,3-triol

70
Q

What is the difference between oil and fat?

A

Oils - liquid at room temperature, not saturated
Fats - solids at room temperature, usually saturated

71
Q

What are the products of hydrolysing fats and oils?

A

Propane-1,2,3-triol and sodium salts of the acids that make up the ester (hydrolysed with NaOH)

72
Q

What are the uses of propane-1,2,3-triol and sodium salts?

A

Soaps and cleaning products

73
Q

What does the long hydrocarbon chain of the carboxylate ion do?

A

Mixes with grease

74
Q

How does the carboxylate ion with a long carbon chain make a good cleaning agent?

A

Grease can be removed from water

75
Q

What is the systematic name of glycerol?

A

Propane-1,2,3-triol

76
Q

What are some common uses of glycerol?

A
  • Used to make pharmaceuticals and cosmetics
  • Solvent in many medicines
  • Solvent in food industry - making dyes
  • Plasticising various materials like cellophane and paper
77
Q

How do you make biodiesel with the general equation and conditions?

A

NaOH catalyst, 60°C
Lipids (fats/oils - esters) + 3CH3OH -> 3 methyl esters + glycerol

78
Q

What does transesterification mean?

A

Converting one type of ester to another

79
Q

What kind of crops is biodiesel made from?

A

Rapeseed oil or soybean oil

80
Q

How is the reaction mixture of biodiesel purified and separated?

A
  1. Settling tank or centrifuge - remove remainder with water
  2. Add acid to neutralise excessa alkali catalyst
  3. Solid soap is formed - easy to remove
81
Q

What is a problem with producing biodiesel?

A

Crops that could be used to make food are being used to make fuel - are the resources being used in the best way?

82
Q

What are caboxylic acid derivatives?

A

Molecules that have the acyl group as part of their structure - formed from carboxylic acids

83
Q

What are 2 carboxylic acid derivatives and their functional groups?

A

Acyl chlorides: RCOCl
Acid anhydrides: RCOOCR / (RCO)2O

84
Q

What is the name of the mechanism and reaction for a nucleophile and an acid derivative?

A

Nucleophilic substitution eliminations
Acylation

85
Q

What 3 factors determine how readily available the acylation of a nucleophile by an acid derivative occurs?

A
  1. Magnitude of the delta + charge on the carbonyl carbon, which depends on the electronegativity of the atom/group being substituted
  2. How easily the atom/group being substituted is lost
  3. How good the nucleophile is (how readily available it will donate electrons)
86
Q

What effect do the Cl and O atoms in acyl chlorides/acid anhydrides have on the partial charge of the carbonyl carbon?

A

Increase the partial + charge by attracting electrons - this means that they react more readily with nucleophiles

87
Q

Are acyl chlorides or acid anhydrides more reactive?

A

Acyl chlorides

88
Q
A
89
Q

What is the name of the mechanism by which acyl chlorides and acid anhydrides acylate nucleophiles?

A

Nucleophilic-addition elimination

90
Q

If the nucleophile is ammonia for the acylation of acyl chlorides or acid anhydrides, what are the products of the reaction?

A

An amide

91
Q

What is the equation for the reaction of ethanoyl chloride and ammonia?

A

CH3COCl + 2NH3 -> CH3CONH2 + NH4Cl

92
Q

If the nucleophile is a primary amine, what is the product of the acylation of acyl chlorides or acid anhydrides?

A

N-substituted amide

93
Q

What is the equation for the reaction of ethanoyl chloride and methylamine

A

CH3COCl + CH3NH2 -> CH3CONHCH3 + CH3NH3Cl

94
Q

If the nucleophile is an alcohol, what is the product of the acylation of acyl chlorides or acid anhydrides?

A

An ester

95
Q

What is the equation for the reaction of ethanoyl chloride and ethanol?

A

CH3COCl + CH3CH2OH -> CH3COOCH2 + HCl

96
Q

If the nucleophile is water, what is the product of the acylation of acyl chlorides or acid anhydrides? What is the name of this reaction?

A

Carboxylic acid
Hydrolysis

97
Q

What is the equation for the reaction of ethanoyl chloride and water?

A

Ch3COCl + H2O -> CH3COOH + HCl

98
Q

What is a commercially important acylation reaction?

A

The manufacture of aspirin

99
Q

What are the advantages of using ethanoic anhydride as an acylating agent over ethanoyl chloride?

A

It’s cheaper, less corrosive and doesn’t react as readily with water, safer as HCl is corrosive and is a toxic gas

100
Q

What would you observe in a melting point determination if the sample was not pure?

A
  • Sample melts over a large range (more than 3°C)
  • Sample’s melting point is below the accepted value due to impurities disrupting the structure
101
Q

Why might the melting point appear different to the true value?

A

Temperature of the material in the machine may be different to the temperature shown on the thermometer - apparatus error

102
Q

When removing flue gases what are the issues?

A

Disposal of large amounts of CaSO3 and CO2 is poduced

103
Q

What conditions are needed to form methyl esters from an acid anhydride or acyl chloride?

A

React with methanol and heat gently under reflux

104
Q

When purifying by recrystallisation, why is the minimum volume of hot solvent used?

A

So that a saturated solution is created, so that as many crystals will fall out of solution as possible when it’s cooled

105
Q

Why is the solution filtered hot when purifying by recrystallisation?

A

To remove insoluble impurities and ensure that the crystals do not form in the filter paper

106
Q

Why is the solution cooled in an ice bath when purifying by recrystallisation?

A

To ensure that as many crystals as possible fall out of solution - yield is higher

107
Q

Why are the crystals washed with cold water when purifying by recrystallisation?

A

To remove soluble impurities

108
Q

How would you separate the crystals from the reaction mixture when purifying by recrystallisation?

A

Filter under reduced pressure using a Buchner funnel

109
Q

Why might a percentage yield be below 100% (practical reasons)?

A
  • Product is lost during filtration, drying and weighing - spills, not all transferred from one piece of apparatus to the other
  • Product is left dissolved in the solution - some does not crystallised, some left on filter paper, sample still wet

Chemistry (16 decks)

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