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A - Chemistry > Unit 3: Section 5 - Isomerism and Carbonyl compounds MDY * > Flashcards

Unit 3: Section 5 - Isomerism and Carbonyl compounds MDY * Flashcards

optical isomerism * aldehydes and ketones carboxylic acids and esters more on esters acyl chlorides purifying organic compounds

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1
Q

what is stereoisomerism?

A

stereoisomers have the same structural formula, but have their atoms arranged differently in space e.g. optical isomerism

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2
Q

what is a chiral carbon atom?

A

one that has four different groups attached to it.

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3
Q

what are optical isomers

A

it’s possible to arrange the groups in 2 different ways around a chiral carbon atom so that 2 different molecules are made

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4
Q

what are enantiomers?

A

mirror images and no matter which way you turn them, they can’t be superimposed

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5
Q

what is plane polarised light?

A

normal light vibrates in all directions. plane-polarised only vibrates in one direction

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6
Q

what does optically active mean?

A

optical isomers are actively active because they rotate plane-polarised light

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7
Q

what affect do enantiomers have on plane polarised light?

A

one enantiomer rotates it in a clockwise direction, and the other rotates it in an anticlockwise direction by the same amount. changing concentration will change the magnitude but not the direction of rotation

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8
Q

what is a racemate/ racemic mixture?

A

it contains equal quantities of each enantiomer of an optically active compound

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9
Q

what does racemates do?

A

they don’t show any optical activity - the 2 enantiomers cancel each other’s light rotating effect.

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10
Q

how are racemic mixtures formed?

A

when 2 achiral things are reacted together to form a chiral product, there’s an equal chance of forming each of the enantiomers. forming a racemate

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11
Q

what shape do double bonds form?

A

e.g. C=O and C=C

they are planar.

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12
Q

how do aldehydes and unsymmetrical ketones form racemic mixtures?

A

e.g. propanal with KCN
this is a nucleophilic addition reaction, the CN can attack the carbon from above or below.
the electrons in the double bond move to the O, then the electrons attract an H+ to make a hydroxyl group

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13
Q

what does achiral mean?

A

optically inactive, it will have no effect on the rotation of polarised light

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14
Q

what physical properties are different in enantiomers?

A

their effect on plane polarised light

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15
Q

what chemical properties are different in enantiomers?

A

their reaction with other chiral compounds

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16
Q

how is the effect of enantiomers on plane polarised light measured?

A

by a polarimeter

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17
Q

what are the problems with racemic drugs?

A

enantiomers can have unequal degrees of physiological activity, different activities or convert in vivo
this causes problems with cost of manufacturing an enantiomer that isn’t needed, separation of unwanted enantiomer, resources being used that are not required

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18
Q

what are cyclical optical isomers?

A

the chiral carbon has different sequences of carbon chain attached to each side and only has 1 hydrogen attached.
so it is affectively unsymmetrical and has 4 different group attached to it

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19
Q

what are carbonyl compounds?

A

compounds that contain a carbonyl functional group C=O

e.g. aldehydes and ketones

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20
Q

what are aldehydes?

A

aldehydes have C=O at end of carbon chain

the name ends in -al

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21
Q

what are ketones?

A

have C=O in the middle of carbon chain
name ends in -one
number of carbon with =O is stated

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22
Q

what happens when oxidising agents react with aldehydes and ketones?

A

aldehyde + [O] —> carboxylic acid

ketones are not oxidised

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23
Q

what oxidising agents can be used to distinguish between aldehydes and ketones?

A

Tollens’ reagent

Fehling’s solution

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24
Q

what does Tollens’ reagent do?

A

colourless solution of silver nitrate dissolved in aqueous ammonia
when heated in a test tube with an aldehyde Ag+ ions are reduced to Ag atoms and a silver mirror forms
ketones don’t react

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25
Q

what does Fehling’s solution do?

A

blue solution of copper(II) ions dissolved in sodium hydroxide
if heated with an aldehyde the copper (II) ions are reduced to a brick-red precipitate of copper (I) oxide
ketones don’t react

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26
Q

how are aldehydes and ketones reduced?

A

LiAlH4 in dry ether
NaBH4 dissolved in water with methanol is usually used as a reducing agent
[H] is used in equations

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27
Q

what happens when potassium cyanide reacts with carbonyls?

A

hydroxynitriles are produced

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28
Q

how does potassium cyanide act as a nucleophile?

A

KCN dissociates in water
CN- group attacks partially positive carbon atom and donates a pair of electrons. both electrons from double bond transfer to oxygen
H+ ions add to oxygen to form hydroxyl group.
RCHO + KCN –> RCH(OH)CN + K+

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29
Q

what are the dangers of reacting potassium cyanide with a carbonyl?

A

potassium cyanide is an irritant and is also extremely dangerous if it’s ingested or inhaled.
it can react with moisture to produce hydrogen cyanide, a highly toxic gas

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30
Q

how can risks be reduced when using potassium cyanide?

A

wear gloves, safety goggles and a lab coat and perform the experiment in a fume cupboard

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31
Q

what are carboxylic acids?

A

contain -COOH functional group

names end in -oic acid

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32
Q

what happens when carboxylic acids are put in water?

A

they are weak acids
they partially dissociate into carboxylate ions and H+ ions
RCOOH RCOO- + H+

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33
Q

what happens when carboxylic acids react with carbonates?

A

carboxylic acid + carbonate(CO3 2-) –> salt + CO2 + H2O

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34
Q

what is esterification?

A

by heating a carboxylic acid and an alcohol in the presence of a strong acid (H2SO4) catalyst
esters and water are formed

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35
Q

what are esters?

A 
contain a COO- group
R
 |
C =O
 |
O - R
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36
Q

How is an ester named?

A

the first part is from the alcohol with yl on the end
e.g. propanol become propyl-
second part is salt name of carboxylic acid -oate
so propanol + ethnic acid
makes
propyl ethanoate

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37
Q

what can esters be used for?

A

perfumes
flavourings
solvents - glues and printing inks
plasticers

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38
Q

how are esters used in perfumes and flavourings?

A

they have a sweet smell

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39
Q

how are esters good solvents?

A

they are polar liquids so lots of polar organic compounds will dissolve in them.
also have low boiling points, so evaporate easily from mixtures

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40
Q

how are esters used in plastics?

A

added to plastics during polymerisation make the plastic more flexible. over time, plastic molecules escape through and plastics become brittle and stiff

41
Q

what is ester hydrolysis?

A

an ester is split into an acid and an alcohol by reflux with a dilute acid
R-COO-R + H2O RCOOH + ROH

42
Q

what is base hydrolysis?

A

refluxing an ester with a dilute alkali to get a carboxylate ion and an alcohol
R-COO-R + OH- —> RCOO- + ROH

43
Q

what are fatty acids?

A

long chain carboxylic acids, they can be saturated or unsaturated

44
Q

what are triglycerides?

A

esters formed by 3 fatty acids combining with glycerol.

these are fats and oils

45
Q

what are animal fats?

A

have mainly saturated hydrocarbon chains
they fit together neatly, increasing van der waals so high temperatures needed to melt them
solid at room temperature

46
Q

what are vegetable oils?

A

they have unsaturated hydrocarbon chains
the double bonds mean chains are bent and don’t pack together well, decreasing van der waals
easier to melt
liquids at room temperature

47
Q

what happens when fats and oils are hydrolysed?

A

like any ester they can be hydrolysed by heating them with sodium hydroxide to produce a salt

48
Q

how is biodiesel made?

A

when vegetable oils are reacted with methanol using potassium hydroxide as a catalyst
a mixture of methyl esters of fatty acids are formed (biodiesel)

49
Q

what is the reaction for the formation of biodiesel?

A

triester + 3CH3OH -KOH-> glycerol + 3RCOOCH3

50
Q

what are acyl chlorides?

A

have the functional group COCl
names end in -oyl chloride
e.g. ethanoyl chloride
CH3COCl

51
Q

what do Acyl chlorides react with?

A 
water
alcohols
ammonia
primary amines
the H is replaced and added to the Acyl where the chlorine was
52
Q

what happens when Acyl chlorides react with water?

A

react vigorously with cold water producing a carboxylic acid and HCl

53
Q

what happens when Acyl chlorides react with alcohols?

A

react vigorously at room temperature to produce an ester and HCl

54
Q

what happens when Acyl chlorides react with ammonia?

A

violent reaction at room temp to produce an amide and HCl

55
Q

what happens when Acyl chlorides react with primary amines?

A

violent reaction at room temp producing an N-substituted amide and HCl

56
Q

what is an acid anhydride?

A

made from 2 identical carboxylic acid molecules.
the name is the same but with anhydride instead of acid
water is also formed from the 2 OH groups

57
Q

what happens when acid anhydrides react with water, alcohol, ammonia and amines?

A

the reactions are very similar to the reaction with Acyl chlorides, but reactions are less vigorous and carboxylic acids are formed instead of HCl

58
Q

what is a nucleophilic addition-elimination reaction?

A

in acyl chlorides the chlorine and oxygen pulls electrons towards themselves so the carbon has a slight positive charge
:O- on methanol or water acts as a nucleophile and attack carbon, electrons in C=O bond move to O
electrons from O- move back to double bond. electrons in bond move to chlorine and it comes off.
chlorine bonds to H on methanol and electrons in bond move to positive O from methanol

59
Q

what is aspirin?

A

an ester - made by reacting salicylic acid with ethanoic anhydride or ethanoyl chloride

60
Q

why is ethanoic anhydride used in industry?

A

its cheaper than ethanoyl chloride
its safer to use than ethanoyl chloride as its less corrosive, reacts more slowly with water and doesn’t produce dangerous hydrogen chloride fumes

61
Q

how to remove impurities from an insoluble product?

A

you can use separation to remove any impurities that do dissolve in water

62
Q

what happens in separation?

A

pour mixture into a separating funnel and add water
shake funnel and allow it to settle. the organic layer and the aqueous layer are immiscible so separate into 2 distinct layers
you can open tap and run each layer into separate containers

63
Q

how to remove impurities from a soluble product?

A

solvent extraction can be used

64
Q

what happens in solvent extraction?

A

take an organic solvent in which the product is more soluble than it is in water.
add it to impure product solution and shake
product will dissolve into organic solvent, leaving impurities dissolved in water
solvent containing product can then be run off using a separating funnel

65
Q

what needs to be done after separation to purify a product?

A

organic layer will end up containing trace amounts of water - so it has to be dried

66
Q

how is a purified product dried?

A

add anhydrous salt such as magnesium sulfate or calcium chloride. the salt is used as a drying agent - it binds to any water present to become hydrated.
it will clump together at first, keep adding until it disperses evenly when you swirl the flask
filter mixture to remove solid drying agent

67
Q

how are leftover soluble impurities removed?

A

washing the product
e.g. with aqueous sodium hydrogen carbonate to remove acid and give CO2 gas.
organic product can be removed using a separating funnel

68
Q

what does distillation do?

A

separates out liquids with different boiling points by gently heating a mixture in distillation apparatus

69
Q

method of distillation:

A

connect condenser to round bottomed flask containing impure product in solution
place thermometer near condenser, this will show boiling point of substance evaporating
heat impure product
when thermometer shows boiling point place flask at open end of condenser to collect pure product

70
Q

what is the simplest way to purify a solid product of an organic reaction?

A

recrystallisation - dissolve in hot solvent to make saturated solution, then let cool, so solubility falls an pure crystals form

71
Q

how to carry out recrystallisation?

A

add very hot solvent to impure solid until it dissolves - forming saturated solution
filter through heated funnel to remove insoluble impurities
let solution cool slowly, forming crystals
remove liquid containing soluble impurities by filtering under reduced pressure using Buchner funnel
wash crystals with ice-cold solvent to remove soluble impurities from surface
leave to dry

72
Q

what is a Buchner funnel

A

flat-bottomed funnel with holes in the base that’s sitting in a side-arm flask attached to a vacuum line

73
Q

how to tell if a substance is pure?

A

pure substances have a specific melting and boiling point. if they’re impure, melting point’s lowered and the boiling point is raised and occur across wide range of temperatures

74
Q

how to test purity using melting point?

A

pack small sample of solid into glass capillary tube
place inside heating element
increase temperature until it melts
measure range of temperature from where it begins to melt to when it melts completely
look up melting point in data books and compare

75
Q

how to name a compound with multiple carbonyl groups?

A

the name begins with oxo- numbered based on position of ketone group and ends with -al for the aldehyde

76
Q

what kind of reaction is reduction?

A

a nucleophilic addition reaction
electrons in C=O bond move to O
:H- from NaBH4 moves to C in C=O
this forms an :O- which bonds to H+ from water and makes an OH bond

77
Q

how are nitriles named?

A

the C with the N on it is the first carbon
they are named alkane nitrile
if it has an OH it is called hydroxy alkane nitrile

78
Q

how do nitriles form carboxylic acid?

A

nitriles can be converted to carboxylic acids by heating them under reflux with dilute acid
RCN —-reflux + H+—> RCOOH

79
Q

how is lactic acid made?

A

made from 2-hydroxypropanenitrile

and the nucleophilic addition to a carbonyl

80
Q

how are carboxylic acids named?

A

the first carbon has the carboxylic acid group on it
name ends in -oic
if it has 2 carboxylic acid groups it ends in -dioicacid
e.g. ethane dioicacid

81
Q

what are carboxylic acid salts?

A

the salt formed when a carboxylic acid reacts with a base

they are named by giving the metal of the base and replacing -icacid by -oate

82
Q

what are the physical properties of carboxylic acids?

A

high melting point as pure substances
strong hydrogen bonding between molecules
dimerisation when pure

83
Q

when are carboxylic acids soluble?

A

when they are small
they dissolve because they can hydrogen bond to the water molecules
after the chain is 4 carbons long the solubility rapidly reduces
they stop dissolving because longer hydrocarbon tails of the molecules get between water molecules and break hydrogen bonds

84
Q

how does the hydrocarbon chain length effect carboxylic acid activity?

A

alkyl groups are electron releasing
increasing chain length pushes electron density on to the COO- ion making it more negative and less stable
H+ can be attracted back to the carboxylate ion better
this makes the acid weaker

85
Q

how do halogens effect carboxylic acid activity?

A

halogen groups are electron withdrawing
acids can be strengthened by pulling charge away from the COO- group
this can be done by adding halogens
so the ions are made less negative and more stable
the more electronegative the halogen, the more it withdraws electrons, the stronger the acid

86
Q

how can you make a carboxylic acid?

A

hydrolysis of a nitrile (R-CN)
heat under reflux with dilute HCl

oxidation of an aldehyde/ primary alcohol
with excess acidified dichromate under reflux

87
Q

what do carboxylic acids react with?

A

metals to produce a salt and hydrogen
bases to produce a salt and water
carbohydrate (CO3 2-) or hydrogen carbonates (HCO3 -) to produce a salt, carbon dioxide and water

88
Q

what is acid hydrolysis?

A

the reverse reaction of esterification (reversible reaction)
ester + H2O —-> acid + alcohol
catalyst = concentrated sulphuric acid

89
Q

what is saponification

A

when alkali hydrolysis goes to completion rather than making a mixture
ester + alkali —–> carboxylic acid salt + alcohol

90
Q

what does saponification of lipids do?

A

it produces salts of fatty acids and glycerol

this mixture is used as soap and is often made by boiling lipids with potassium hydroxide

91
Q

what is acylation?

A

adding an acyl group to a molecule
it happens when the H on the O of an alcohol/water is replaced by an acyl group
the H on the N of an amine/ ammonia is replaced by an acyl group
the other product is an acid

92
Q

what is transesterification?

A

biodiesel can be made from lipids
lipid is broken down into 3 fatty acids and glycerol by potassium hydroxide
fatty acids are converted into 3 new esters using methanol
KOH acts as catalyst

93
Q

what is ammonia?

A

NH3

94
Q

what is ammonium?

A

NH4 +

95
Q

what is a nitrile?

A

R-CN

96
Q

what is an amine?

A

R -NH2

97
Q

what is an amide?

A 
R
 |
C=O
 |
NH2
98
Q

what is an N substituted amide?

A

R-C(=O) - NH - R

A - Chemistry (26 decks)

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