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Chemistry Y13 > Isomerism 2 > Flashcards

Isomerism 2 Flashcards

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1
Q

Optical isomerism

A
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2
Q

What is optical isomerism?

A

optical isomerism occurs when a carbon atom has four different atoms or groups of atoms attached to it.

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3
Q

What do all optical isomers have?

A

asymmetrical atom or a chiral centre

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4
Q

When a molecule has a chiral centre..?

A

there are 2 non-superimposable isomers that are mirror images of each other

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5
Q

give an example of optical isomerism?

A

2-chlorobutane - chlorine group, ethyl group, methyl group and a hydrogen atom attached

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6
Q

what does non-superimposable mean?

A

means you can not stack one form exactly on top of the other.

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7
Q

what categories do spoons fall into?

A

mirror images and superimposable

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8
Q

what categories do books fall into?

A

superimposable but not mirror images

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9
Q

what categories do hands fall into?

A

non-superimposable and mirror images

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10
Q

for optical isomerism which two categories do they need to fall into?

A

must be non-superimposable and mirror images

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11
Q

what is the difference between optical isomers and enantiomers?

A

Enantiomers have the same physical properties except that they differ in their effect on the plane of polarised light (instead they are optically active)

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12
Q

when does plane-polarised light vibrate?

A

only in one plane

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13
Q

How many enantiomers can we have?

A

2

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14
Q

in which ways will these enantiomers rotate?

A

one enantiomer will rotate the plane of the polarised light clockwise (+)

the other enantiomer will rotate the plane of polarised light anticlockwise (-)

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15
Q

how can we measure the rotation of light?

A

using a polarimeter

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16
Q

how exactly does this work?

A

by observing the polarised light coming out towards the observer

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17
Q

Which two forms can enantiomers take?

A

Dextrorotary and Laevorotary

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18
Q

If an enantiomer takes the Dextrorotory form then..?

A

the light appears to have turned to the right (clockwise) to form a positive (+) dextrorotary enantiomer

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19
Q

If the enantiomer takes a Laevorotary form then light…?

A

appears to have taken a left turn (anticlockwise) to form a negative enantiomer (-)

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20
Q

Draw out the polarimeter and label which each part does what

A

A - light source produces light vibrating in all directions
B - polarising filter only allows through light vibrating in one direction
C - plane polarised light passes through the sample
D - if substance is optically active it rotates the plane of polarised light
E - analysing filter is turned so that light reaches a maximum
F - direction of rotation is measure coming towards the observer

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21
Q

what would be classed as an optically inactive mixture?

A

a mixture of equal amounts of both enantiomers (50:50) is optically inactive because the optical effects of each enantiomer cancel each other out

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22
Q

And what would this mixture be referred to as?

A

Racemate/ racemic mixture

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23
Q

Optical isomerism is important in..?

A

Biochemistry

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24
Q

why is only one enantiomer formed in nature?

A

when optically active molecules are made in nature, only one enantiomer is formed. this is because biological systems involve enzymes that are stereospecific in their action.
*in nature, the molecule is made by enzymes that are stereospecific in their action.
* the enzyme will be a single enantiomer that will only react with one enantiomer to make a single enantiomer.

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25
Q

What biological system is an example of something opticaly active?

A

enzymes

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26
Q

How many enantiomers can enzymes react with?

A

only one enantiomer and can only produce one enantiomer as a result of a reaction

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27
Q

Give an example

A

only the (+) enantiomer of glucose is absorbed by the human body. the (-) enantiomer passes through the body unchanged.

Also amino acids exist as single enantiomers too e.g alanine

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28
Q

the properties of all optically active enantiomers are..?

A

all identical

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29
Q

the properties of optically active enantiomers are all identical except…?

A

in reactions with other optically active substances

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30
Q

what is meant by enzymes are sterospecific?

A

they can distinguish between enantiomers and catalyse the reactions of only one pair of isomers

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31
Q

why can enantiomers have different smells?

A

this is because our sense receptors are chiral protein molecules

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32
Q

what molecules is naturally occurring chemical with two enantiomers?

A

Carvone

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33
Q

what does carvone taste like?

A

one tastes like caraway seeds while the other has a spearmint flavour

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34
Q

Chirality in the pharmaceutical industry

A
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35
Q

What is drug action determined by and why can Drug action can have different effects?

A

drug action can be determined by the stereochemistry of the molecule and different optical isomers can have different effects

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36
Q

In optically active drugs only…?

A

one enantiomer will produce an effect on the body

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37
Q

if only one enantiomer works, why are drugs usually a racemic mixture?

A

for economical reasons - separation of the enantiomers is very costly

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38
Q

What drug is a chiral molecule and can exist as two enantiomers?

A

Thalidomide

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39
Q

What was Thalidomide used for?

A

used to treat anxiety and morning sickness in pregnant women

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40
Q

what did side effects did this have?

A

many gave birth to children with deformities and missing limbs

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41
Q

After research, how thalidomide caused birth defects, explain how?

A

it turned out only one enantiomer was effective and safe, its optically active counterpart was not. The major problem was that a mixture of isomers was formed.
( after than was banned worldwide but still babies left with defects)

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42
Q

why have drug companies been encouraged to develop single enantiomer products/drugs?

A

such products are safer and more effective than the racemate

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43
Q

Give an example of a single enantiomer drug?

A

Ibuprofen acts much faster as the (+) enantiomer than when administered as a racemate

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44
Q

Questions

A
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45
Q

explain why the compound CH3CH2(NH2)COOH can exist as an enantiomer?

A

It can exist as an enantiomer as it has a chiral structure. there are 4 different groups are attached to the 2nd carbon

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46
Q

explain why the compound CH3CH(NH2)COOH occur only in nature as a (-) enantiomer?

A

In nature, the molecule is made by enzymes that are stereospecific in action. The enzyme will be a single enantiomer that will only react with one enantiomer to make a single enantiomer

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47
Q

Draw two enantiomers of the above carboxylic acid

A
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48
Q

After exercise Lactic acid builds up in the muscle cells of the body and causes fatigue. what will be the difference between this lactic acid and that prepared in a laboratory?

A

Muscle cell lactic acid will be a single enantiomer (made by enzymes that are stereospecific in their action.) Which will rotate the plane of polarised light. Lab made lactic acid will be a racemate mixture (50:50 of both enantiomers) and wll not rotate the plane of polarised light - optical effects cancel out.

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49
Q

How could we differenciate between 2 optical isomers of lactic acid?

A

One will rotate the plane of polarised light clockwise (+) and one will rotate the plane of polarised light anticlockwise (-) by the same amount

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50
Q

Aldehydes and Ketones - oxidation and reduction

A
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51
Q

Why is the carbon oxygen bond polar? also why does it react with acid?

A
  • the oxygen atom is more electronegative than the carbon atom
  • the oxygen atom draws the electrons in the double bond towards itself
  • the oxygen atom becomes slightly neg(-) charges and the carbon becomes slightly pos(+) charged
  • the pos(+) carbon atom is electron deficient and is attacked by nucleophiles readily
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52
Q

what are nucleophiles?

A

lone pair of electrons that can donate to form a covalent bond

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53
Q

What are alcohols oxidised by?

A

Acidified potassium dichromate

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54
Q

what are primary alcohols oxidised to form?

A

aldehydes

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55
Q

secondary alcohols are oxidised to form?

A

ketones

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56
Q

general formula for aldehydes and ketones?

A

CnH2nO

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57
Q

what is the difference between aldehydes and ketones?

A

aldehydes have a hydrogen atom attached to the carbonyl atom

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58
Q

What is the test for aldehydes?

A

aldehydes can be further oxidised to carboxylic acids in an excess of the oxidising agent.

(so aldehydes are mild reducing agents)

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59
Q

Tollen’s reagent results for both aldehyde and ketone?

A

when tollens is warmed with an aldehyde a silver mirror is produced, the aldehyde has been oxidised to a carboxylic acid.

ketones do not react with tollens

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60
Q

Fehlings solution results when warmed with an aldehyde?

A

when an aldehyde is warmed with fehlings a brick red precipitate is formed. the aldehyde is oxidised to a carboxylic acid

ketones do not react with fehlings

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61
Q

Reduction of Aldehydes and Ketones

A
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62
Q

aldehydes can be reduced to…?

A

primary alcholos

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63
Q

Ketones can be reduced to..?

A

secondary alcohols

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64
Q

How can reduction of aldehydes and ketones take place, by which processes?

A

Catalytic hydrogenation and reactions with reducing agents such as NaBH4

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65
Q

Catalytic hydrogenation

A
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66
Q

What catalyst is used to reduce Aldehydes and ketones?

A

Nickel catalyst

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67
Q

why can the C=O bond go undergo catalytic hydrogenation in the same way as C=C?

A

because the C=O bond is saturated in the same way that C=C bond is saturated when alkenes undergo catalytic hydrogenation

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68
Q

what happens when these bonds undergo catalytic hydrogenation

A

these bonds become saturated

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69
Q

Show a displayed formula of the catalytic hydrogenation of butanone?
what temperature is needed for this reaction?

A

150 DEGREES

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70
Q

How are aldehydes and ketones reduced using NaBH4?

A

aldehydes and ketones are reacted with sodium tetrahydridoborate(III) and adds hydrogen via a nucleophilic attack on the slightly positive carbon of the carbonyl group

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71
Q

why can nucleophiles not attack alkenes?
therefore..?

A

electron rich double bond repels nucleophiles. therefore, reagents such as NaBH4 can be used to SELECTIVELY REDUCE aldehydes and ketones

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72
Q

What are the reaction conditions needed for the Nucleophilic addition of the hydride ion?

A
  • NaBH4 OR LIBH4 in aqueous solution
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73
Q

Draw out the full mechanism of the nucleophillic addition of the hydride ion.
explain this mechanism in steps

A
  1. carbonyl group of an aldehyde or ketone is attacked by a nucleophile, an addition rection occurs and the carbon double bond becomes a single bond
  2. reagents such as NaBH4 and LiBH4 provide the hydride ion (:H-)
  3. An oxyanion intermediate is formed which gains a proton (H+) from the solvent (e.g water/weak acid)
  4. the reaction with NaBH4 is normally carried out in aqueous solution
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74
Q

Show the mechanism for the reduction of ethanal by NaBH4

A
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75
Q

Show the mechanism for the reduction of propanone by NaBH4

A
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76
Q

why is reduction using NaBH4 preferred to reduction using Catalytic hydrogenation in compounds that have multiple functional groups?

A

NaBH4 is capable of selectively reducing the carbonyl group. H2/Ni does not select what it reduces - tends to reduce anything present that can be reduced

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77
Q

In what conditions does Reduction with NaBH4 take place?

A

In Aqueous conditions

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78
Q

Nucleophilic addition reaction of aldehydes and ketones with KCN followed by dilute acid

A
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79
Q

what do Aldehydes and ketones form when undergoing nucleophilic reactions with KCN and dilute acid

A

hydroxynitriles

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80
Q

Draw the reaction mechanism for nucleophilic addition reaction of aldehyde (ethanal) and ketone (butanone + propanone) with KCN followed by dilute acid. explain the mechanism in steps + include the final products

A

the :CN- (from the KCN) acts as a nucleophile and attacks the electron deficient slight positive carbon atom of the carbonyl group
- the anion then gains a proteon from the (H+) from the dilute acid

Products aldehyde: 2-hydroxypropanenitrile

products butanone: 2-hydroxy-2-methylbutanenitrile

products propanone: 2-hydroxy-2-methylpropanenitrile

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81
Q

When is a chiral centre produced in a ketone?

A

only when the starting ketone is asymmetrical

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82
Q

Nucleophilic addition of hydrogen cyanide to aldehydes and ketones

A
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83
Q

what do aldehydes and ketones form with hydrogen cyanide?

A

hydroxynitriles

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84
Q

why is this reaction rarely carried out?

A

due to the highly toxic nature of HCN gas

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85
Q

What is the overall equation for the reaction between ethanal and Hydrogen cyanide?

A

—> 2-hydroxypropanenitrile
CH3CHO + HCN —-> CH3CH(OH)CN

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86
Q

What is the overall equation for the reaction between butanone and Hydrogen cyanide?

A

—-> 2-hydroxy-2-methylbutanenitrile
CH3COCH2CH3 + HCN —> CH3CH2C(OH)(CH3)CN

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87
Q

What is the overall equation for the reaction between propanone and Hydrogen cyanide?

A

—-> 2-hydroxy-2-methylpropanenitrile
CH3COCH3 + HCN —> (CH3)2C(OH)CN

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88
Q

What are the hazards of using KCN?

A
  • KCN is highly toxic and HCN is extremely toxic and can lead to death
  • If there is a risk of HCN a fume cupboard should be used
  • hydrogen cyanide is also highly flammable
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89
Q

why is the addition of the -CN group very useful in organic synthesis?

A

because it increases the number of carbon atoms in the molecules and so increases the chain length

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90
Q

What are the other advantages of the -CN group?

A
  • easily converted into other functional groups once it has been added to a molecule
  • the -CN can be converted into a -COOH (a carboxylic acid by hydrolysis
  • the -CN group can be reduced to -CH2NH2 (an amine) by catalytic hydrogenation
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91
Q

How can 2-Hydroxypropanenitrile be hydrolysed and reduced to form what products?

A

CH3CH(OH)CN ——H2O+H+—-> CH3CH(OH)COOH (hydrolysis to form carboxylic acid)

CH3CH(OH)CN —– H2/N2—–> CH3CH(OH)CH2NH2 (reduced via catalytic hydrogenation to form a amine)

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92
Q

the reaction of aldehydes and ketones with acidified KCN produces racemic mixture.

A

Title

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93
Q

what happens when ethanal is reacted with KCN. What does it produce?

A

forms 2-hydroxypropanenitrile - which has a chiral centre

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94
Q

when this product is made in a labarotory what is produced?

A

an optically inactive (+_) racemic mixture

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95
Q

what is a racemic mixture?

A

a mixture of equal amounts of each enantiomer (50:50) and is optically inactive because both of the optical effects of each enantiomer cancel out

96
Q

why is a racemic mixture produced?

A

because the carbonyl group is planar so attack by the :CN- nucleophile is equally likely from either side of the plane

97
Q

What does the hydrolysis (in acidic conditions) of 2-hydroxypropanenitrile lead to?

A

the formation of the racemate ( ±) 2 hydroxypropanoic acid (lactic acid)

98
Q

where is this mixture (±) of lactic acid found?

A

in sour milk

99
Q

when is the (+) enantiomer of lactic acid formed?

A

during the contraction of muscle cells

100
Q

reduction of an unsymmetrical ketone gives a? Give an example of a reaction?

A

racemic mixture
e.g CH3COCH2CH3 + 2[H] ——–> CH3CH(OH)CH2CH3
(butanone makes butan-2-ol)

101
Q

why is a racemic mixture produced when a ketone is reduced?

A

carbonyl group is planar so attack by the nucleophile is equally likely from both sides of the plane

102
Q

When But-2-ene reacts with HBr in an electrophilic addition reaction, what is formed? why?

A

A racemic mixture of 2-Bromobutane
because the C=C double bond is planar so attack by the H-Br electrophile is equally likely from either side of the plane

103
Q

Write a series of reactions to show how 2-hydroxypropanoic acid can be synthesised from ethanol.

A
  1. oxidation of ethanol to produce ethanal
    2, then we can react ethanal with potassium cyanide followed by dilute acid. to form 2-hydroxypropanenitrile
  2. Acidic hydrolysis of 2-hydroxypropanenitrile makes 2-hydroxypropanoic acid (reagents = h20/h+)
104
Q

Carboxylic acids and Esterification

A
105
Q

what is the functional group of carboxylic acids?

A

COOH - also refferred to as the carboxyl group

106
Q

How do we name carboxylic acids?

A

we begin from the COOH group - so this is carbon number 1

107
Q

what is this also the same for?

A

same for other functional groups such as nitriles, aldehydes

108
Q

How are carboxylic acids made?

A

by oxidising a primary alcohol or an aldehyde

109
Q

what are primary alcohols oxidised by?
to form?

A

acidified potassium dichromate 6 to form aldehydes
ethanol + [O] ——-> ethanal + water

110
Q

these aldehydes can be further oxidised by..? to form?

A

an excess of Acidified potassium dichromate 6 to form a carboxylic acid

111
Q

What is the main property of a carboxylic acid?
What does this allow carboxylic acids to do?

A

it’s a weak acid
so can react with metals, bases (alkali’s) - neutralisation and metal carbonates and hydrogencarbonates

112
Q

when reacted with metals what does a carboxylic acid make?

A

metal + acid ——> salt and Hydrogen

113
Q

draw a symbol and word equation to show the reaction between magnesium and ethanoic acid?

A

Mg + 2CH3CHOOH ——–> (CH3COO-)2 Mg2+ + H2
magnesium + ethanoic acid ——–> magnesium ethanoate + hydrogen

114
Q

when reacted with bases, what do carboxylic acids make?

A

Base + acid —–> salt + water

115
Q

Draw a symbol and word equation to show the reaction between sodium hydroxide and ethanoic acid.

A

NaOH + CH3COOH ———–> CH3COO-Na+ + H2O
sodium hydroxide + ethanoic acid ——-> sodium ethanoate + water

116
Q

what does a metal carbonate and a metal hydrogencarbonate make when reacted with a carboxylic acid?

A

Salt + water + CO2

117
Q

Draw a symbol and word equation to show the reaction between calcium carbonate and propanoic acid.

A

CaCO3 + 2 CH3CH2COOH ——-> (CH3CH2COO-)2 Ca2+ + H2O + CO2
calcium carbonate + propanoic acid ——> calcium propanoate + water + co2

118
Q

Draw a symbol and word equation to show the reaction between sodium hydrogencarboate and ethanoic acid.

A

NaHCO3 + CH3COOH —–> CH3COOH- Na+ + H2O + CO2
sodium hydrogencarbonate + ethanoic acid ——> soium ethanoate + water + co2

119
Q

what is the test and positive result for a carboxylic acid?

A

Sodium hydrogen carbonate - bubbles of CO2 gas

120
Q

explain why carboxylic acids, have a low Ka value?

A

they are weak acids, so only slightly disassociate with water

121
Q

what is the carboxylate anion?

A

part of the salt made when carboxylic acids react tor form a salt

122
Q

what is the charge on the carboxylate anion?

A

single negative charge - the single negative charge is shared between the two oxygens

123
Q

Draw a diagram to show how the single charges are shared between the 2 oxygen atoms

A
124
Q

Esterification

A
125
Q

How are esters made?

A

reacting carboxylic acids with alcohols in the presence of a small quantity of a strong acid catalyst (concentrated sulphuric acid H2SO4) to make esters

126
Q

What type of reaction is esterification?

A

reversible

127
Q

what is the functional group of esters?

A

COOR
R - is an alkyl group

128
Q

Water is eliminated in the reaction, so is also referred to as a….?

A

condensation reacation

129
Q

why is this way of making an ester not good?

A

because the reaction is reversible and so there is a low yield

130
Q

Draw a word equation to show what a carboxylic acid + alcohol makes an ester

A

carboxylic acid + ester —> conc h2SO4 –> ester + water

131
Q

Write equations and draw the displayed formula of the reactants and products for the following reactions :

A

Move to next sildes

132
Q

ethanoic acid and ethanol ———->

A

ethyl ethanoate and water

133
Q

propanoic acid and butan-1-ol ———->

A
134
Q

2-methylpropanoic acid + butan-2-ol ——–>

A
135
Q

Benzene carboxylic acid + propan-1-ol —–>

A
136
Q

Esters

A
137
Q

how are esters made and what type of reaction is esterification?

A

carboxylic acids react with alcohols in the presence of concentrated sulphuric acid to make esters (a reversible reaction)

138
Q

esters have…? smells?
what do esters smell like?

A

pleasant - often described as having a sweet and fruity smell

139
Q

what are esters commonly used in?

A
  1. perfumes
  2. artificial food flavourings
  3. plasticisers (make polymers more flexible)
  4. solvents (for polar organic compounds)
140
Q

when drawing esters, we draw the part of the ester which is derived from the acid on the.. and the part of the aclcohol on the…?

A

acid first (on the left) and then the part of the alcohol on the right

141
Q

But when naming ester, the name of the ester which is derived from the acid is …. and the part from the alcohol is..?

A

acid is written after the alcohol. The name derived from the alcohol is written first then the acid.

142
Q

the alcohol group is written first as what group?

A

an alkyl group

143
Q

the second part of the name is from the carboxylic acids and named?

A

as an oate - so changes from ethanoic to ethanoate

144
Q

what type of isomers are esters?

A

functional group isomers - same molecular formula different functional group (same func. group as COOH)

145
Q

what is the backwards reaction of esterification?

A

ester hydrolysis

146
Q

Esters can undergo hydrolysis in two way, what are they?

A

In acidic or alkaline solution

147
Q

how do we hydrolyse an ester in acidic solution?

A

by refluxing an ester with water and in the presence of concentrated sulphuric acid catalyst (H2SO4)

148
Q

Draw a word equation to show this reaction

A

Ester + water——–Conc. H2SO4⇌
carboxylic acid + alcohol

149
Q

draw the word equation to show the acidic hydrolysis of ethyl ethanoate?

A

ethyl ethanoate + water —-Conc. H2SO4 —-> ethanoic acid + ethanol

150
Q

How can we hydrolyse an ester in alkaline solution?

A

esters can be hydrolysed by boiling in NaOH

151
Q

Why is boiling an ester with NaOH solution better?

A

boiling an ester with NaOH is quicker and produces a higher yield of product as the reaction goes to completion.

152
Q

draw a word equation for this hydrolysis?

A

ester + sodium hydroxide —-> sodium salt of carboxylic acid + alcohol

153
Q

draw the symbol equation for this reaction?

A

RCOOR’ + NaOH —–> RCOO- Na+ R’OH

154
Q

Draw the symbol and word equation for the alkaline hydrolysis of methyl ethanoate?

A

methyl ethanoate + sodium hydroxide —–> sodium ethanoate + methanol

CH3COOCH3 + NaOH —-> CH3COO- Na+
+ CH3OH

155
Q

Draw the symbol and word equation for the alkaline hydrolysis of ethyl methanoate?

A

ethyl methanoate + sodium hydroxide —-> sodium methanoate + ethanol

CH3COOCH2CH3 + NaOH ——–>HCOO-Na+ + CH3CH2OH

156
Q

What happens when an excess of dilute HCL or dilute H2SO4 is added to the sodium salt of a carboxylic acid?

A

The carboxylic acid is then reformed

157
Q

Hydrolysis of naturally occurring esters

A
158
Q

What are examples of naturally occurring esters?

A

Fats and oils

159
Q

Why do we hydrolyse naturally occurring esters such as oils and fats?

A

to make useful products such as soap and glycerol

160
Q

give an example of solid esters?
Give an example of liquid esters?

A
  • occurs in animal fats
  • vegetable oils are liquid esters
161
Q

most oils and fats are esters of which glycerol molecule?

A

propane 1,2,3-triol (glycerol) with 3 long chain carboxylic acids (often called fatty acids)

162
Q

What are these esters long chain of fatty acids also called?

A

triglycerides (tri-esters)

163
Q

What are the most common fatty acids (long -chain carbocylic acids) and how and where are they found?

A

a) octadecanoic acid (stearic acid) - a saturated fatty acid (no C=C) - found in animal fats
b) octadeca-9-enoic acid (oleic acid) - cis-mono-unsaturated (1 c=c) - found in most fats and olive oil
c) octadeca-9,12-dienoic acid (linoleic acid) - (2 C=C) - found in vegetable oils (soybean + corn oil )

164
Q

What happens when fats (triglycerides) are boiled with sodium hydroxide?

A

they form glycerol (propane-1,2,3-triol) and a mixture of sodium salts of the 3 component acids - (SOAP) (sodium octadecanoate)

165
Q

draw the word and symbol equation of hydrolysing triglycerides with sodium hydroxide?

A
166
Q

which homologous series does glycerol belong to?

A

alcohol - OH

167
Q

why id glycerol highly viscous?

A

hydrogen bonding occurs between the molecules

168
Q

why is glycerol added to wine?

A

to increase both sweetness and viscosity

169
Q

why does glycerol attract water molecules?

A

glycerol easilt form hydrogen bonds and therefore attracts water.

170
Q

this property of being able to attract water molecules means that glycerol helps to prevent?

A

materials drying up too quickly

171
Q

therefore, glycerol is added to..?

A

cosmetics, food, and glue

172
Q

Biodiesel

A
173
Q

what is biodiesel?

A

an fuel that can be used in normal diesel engines

174
Q

where is biodiesel mainly obtained from?

A

mainly obtained from vegetable oils suh as rapeseed ooils, sunflower oiol, or soybean oil,. (not from crude oil)

175
Q

what are some of the good properties of biofuel?

A

renewable fuel and carbon neutral

176
Q

how can vegetable oils be converted into biodiesel (and glycerol) ?

A

by reacting it with methanol in the presence of a catalyst (base or acid)

177
Q

what is biodiesel a mixture of?

A

a mixture of methyl esters of long-chain carboxylic acids

178
Q

how are these methyl esters formed?

A

in a transesterification reaction

179
Q

what is a transesterification reaction?

A

is a reversible reaction in which an ester reacts with an alcohol (usually in excess) to form a new ester and a new alcohol.

180
Q

Draw an equation which outlines every transesterification reaction?

A

Alcohol + Ester ⇌ New alcohol + New Ester

181
Q

So if we reacted Propyl Butanoate in an excess of methanol with an acid or base catalyst what would be our products?

A

methyl Butanoate + Propan-1-ol

182
Q

And we can apply this to the transesterification of biodiesel ↑

How many moles of an methanol would we need and why?

A

3 moles of the reacting alcohol (methanol) to form 3 new esters

183
Q

draw a word and symbol equation to show the transesterification of vegetable oil (triglycerides) to make biodiesel + glycerol.

A

vegetable oils (triglycerides) + methanol ——-> methyl esters of long-chain fatty acids (BIODIESEL) + glycerol (propane1,2,3-triol)

184
Q

Adding an excess of methanol does what to the reversible reaction?

A

drives equilibrium to the right to increase the yield of biodiesl

185
Q

why do we convert vegetable oil to a mixture of methyl esters of fatty acids?
why is it better?

A

makes the fuel less viscous

186
Q

why is biodiesel mixed with petrodiesel?

A

improves fuel lubricity.

187
Q

what is the advantage of biodiesel than petrodiesel?

A

cleaner burning - so less pollutants made

188
Q

How can the glycerol by-product be used?

A

made into soap, cosmetics, glue and food - however there are new uses for glycerol being explored

189
Q

what is a downside of biodiesel?

A

farmers may stop planting staple food crops in favour of biodiesel cash crops - so might lead to food shortage

190
Q

Acyl chlorides and Acid anhydrides

A
191
Q

what are acyl chlorides and acid anhydrides?

A

derivates of carboxylic acids

192
Q

in Acyl chlorides what is the OH replaced by?

A

CL group/ atom

193
Q

in acid anhydrides what replaces the OH group?

A

RCOO- group

194
Q

what do these replacements do?

A

make the resulting molecule more reactive than the corresponding carboxylic acid

195
Q

what is the functional group of acyl chlorides

A

-COCl functional group

196
Q

why are acyl chlorides attacked by nucleophiles?

A

Both the O and the Cl are more electron negative than the carbon atom. the C=O and the C-Cl bonds are polar. The slightly positive carbon atom is electron deficient and is therefore very readily attacked by nucleophiles

197
Q

how do we name acyl chlorides?

A

the oic acid suffic is replaced by oyl chloride

198
Q

explain why acid anhydrides are readily attacked by nucleophiles?

A

the Oxygen is more electronegative than the slight positive carbon. both oxygens are polar the carbon atom is electron deficient and therefore readily attacked by nucleophiles

199
Q

how do we name acid anhydrides?

A

the oic acid is replaced by oic anhydride

200
Q

what is acylation?

A

is the addition of an acyl group (R-C=O) to a molecule

201
Q

what can both the acid anhydride and acyl chloride provide?

A

the acyl group for the acylation of another molecule

202
Q

what do both acid anhydrides and acyl chlorides have that make them more susceptible to a nucleophilic attack?

A

a slightly positive carbon atom

203
Q

what properties do they both have?

A

good leaving groups, CL- and OCOR respectively

204
Q

what are good leaving groups?

A

‘Good leaving groups’ are stable species that are liberated during a chemical reaction.

205
Q

because acyl chlorides and acid anhydrides have good leaving groups, this makes them more…?

A

reacative than the corresponding carboxylic acids

206
Q

Acyl chlorides and acid anhydrides take part on acylation reactions via which mechanism?

A

they react with nucleophiles via nucleophilic addition-elimination

207
Q

What are the four nucleophiles that attack acid anhydrides and acyl chlorides?

A
  1. water (Hydrolysis)
  2. alcohols
  3. ammonia
  4. primary amines
208
Q

What are the products of the above reaction with acyl chlorides?

A
  1. water forms carboxylic acids
  2. alcohols form esters
  3. Ammonia forms Amides
  4. primary amines form N-substituted amides
209
Q

Name and Draw out the mechanism as well as the symbol and word equation of the reaction between ethanoyl chloride with water, include the products made.

A

reactants: CH3COCL + H20 (Ethanoyl chloride + water0
products: CH3COOH + HCl (ethanoic acids and Hydrogen chloride)

210
Q

Name and Draw out the mechanism and word/symbol equation of the reaction between ethanoyl chloride and methanol, include the products made.

A

Reactants : CH3COCL + CH3OH (Ethanoyl chloride + methanol)
Products: CH3C00CH3 + HCl (Methyl ethanoate + hydrogen chloride)

211
Q

Name and Draw out the mechanism as well as the symbol and word equation of the reaction between ethanoyl chloride and Ammonia, include the products made.

A

reactants: CH3COCL + 2NH3 (Ethanoyl chloride + ammonia
products: CH3CONH2 + NH4Cl ethanamide + Ammonium chloride

212
Q

Name and Draw out the mechanism as well as the symbol and word equation of ethanoyl chloride with Primary amine = methylamine, include the products made.

A

Reactants: CH3COCL + 2CH3NH2 (ethanoyl chloride + methylamine)
Products: CH3CONHCH3 + CH3NH3+CL-
( N-methylethanamide + methyl-ammonium chloride)

213
Q

How do we name amides?

A

the suffic - amide is used when naming amides

214
Q

what is an N-substituted amide?

A

one (or two) of the hydrogen atoms attached o the nitrogen atom have been replaced by an alkyl group
e.g N-ethylpropanamide, there is an ethyl group and a hydrogen attached to the nitrogen instead of two hydrogens

215
Q

Acylation of Acid Anhydrides

A
216
Q

What are the 4 nucleophiles acid anhydrides react with and what products are formed?

A
  1. water (hydrolysis) to form 2 carboxylic acids (no other byproduct made)
  2. Alcohols make ester and (carboxylic acid)
  3. Ammonia makes Amide + (ester)
  4. Primary amine makes a N-substituted amide + (branched ester)
217
Q

name and draw out the mechanism as well as the symbol and word equation for the reaction between ethanoic anhydride and water, include the products made

A

Reactants: (CH3CO)2O + H2O ( ethanoic anhydride + water)
Products: 2 CH3COOH (ethanoic acid)

218
Q

name and draw out the mechanism as well as the symbol and word equation for the reaction between ethanoic anhydride and Methanol, include the products made

A

Reactants: (CH3CO)2O + CH3OH) ( ethanoic anhydride + methanol)
Products: CH3COOCH3 +CH3COOH (methyl ethanoate + ethanoic acid)

219
Q

name and draw out the mechanism as well as the symbol and word equation for the reaction between ethanoic anhydride and Ammonia, include the products made

A

Reactants: (CH3CO)2O + 2NH3) ( ethanoic anhydride + Ammonia)
Products: CH3CONH2 + CH3COO-NH4+ (ethanamide + ammonium ethanoate )

220
Q

name and draw out the mechanism as well as the symbol and word equation for the reaction between ethanoic anhydride and Primary amine = methylamine, include the products made

A

Reactants: (CH3CO)2O + 2NH3) ( ethanoic anhydride + Ammonia)
Products: CH3CONHCH3 + CH3COO-CH3NH3+ (N-methylethanamide + methylammonium ethanoate )

221
Q

Note: May not be asked to draw out mechanisms but examiner may be cheeky

A
222
Q

How can we distinguish between Acid Anhydrides and Acyl Chlorides

A
  • add water
  • measure the pH with a pH meter
  • pH ≈ 3 for ethanoic anhydride
  • pH ≈ 0/1 for acyl chloride
223
Q

why is the pH roughly 3 for an acid anhydride?
Draw out a symbol equation to show this reaction

A

this is because only ethanoic acid (weak acid) is made when ethanoic anhydride reacts with water.
(CH3CO)2O + H20 —-> 2 CH3COOH

224
Q

Why is the pH roughly 0/1 for a Acyl Chloride?

A

This is becuase when ethanoyl chloride reacts with water HCL (strong acid) is also made in addition to ethanoic acid
CH3COCL + H20 —-> CH3COOH + HCl

225
Q

MAKING ASPIRIN

A
226
Q

what is the chemical name for Aspirin?

A

2-ethanoyloxybenzenecarboxylic acid

227
Q

What is Aspirin mostly used for?

A

Aspirin is the most commonly used drug of all time as an analgesic (pain killer)

228
Q

How is Aspirin made?

A

by reacting salicylic acid with either ethanoyl chloride or ethanoic anhydride

229
Q

What is the chemical name for salicylic acid?

A

2-hydroxybenzoic acid

230
Q

Draw a reaction mechanism to show how Aspirin is made by reacting Salicylic with Ethanoyl chloride?

A

makes Aspirin and Hydrogen chloride

231
Q

Draw a reaction mechanism to show how Aspirin is made by reacting salicylic acid with ethanoic anhydride?

A

makes aspirin and ethanoic acid - CH3COOH

232
Q

What are hydroxybenzene molecules?

A

Phenols

233
Q

What can phenols do?

A

Act as nucleophiles

234
Q

Industrially how is aspirin made?

A

aspirin is made by industrially by reacting salicylic acid with ethanoic anhydride

235
Q

What are the advantages of making Aspirin with ethanoic anhydride compared to ethanoyl chloride?

A
  • ethanoic anhydride is cheaper
  • ethanoic anhydride is less corrosive (less dangerous to use)
  • ethanoic anhydride is less reactive and less susceptible to hydrolysis
236
Q

FINISH

A

Chemistry Y13 (13 decks)

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