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[OBSELETE] S - Chem > topic 17 > Flashcards

topic 17 Flashcards

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1
Q

what is optical isomerism a result of

A

optical isomerism is a result of chirality in molecules with a single chiral centre

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2
Q

what does it mean if a molecule is chiral

A

if two objects/ molecules are mirror images of each other and they are not superimposable then they are said to be chiral

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3
Q

what does non-super imposable mean

A

non super imposable means that two images/molecules with the same structure (but one is mirrored) dont match when you put them on top of each other

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4
Q

how does chirality occur

A
  • chirality is a property exclusive to asymmetrical molecules with different groups attached to a central carbon atom
    • has no line of symmetry
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5
Q

how can you identify a chiral centre

A

carbon centre with 4 different groups attached

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6
Q

how can you indicate whether a molecule has a chiral centre

A

using an *

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7
Q

what does it mean if a molecule has a chiral centre

A

two possible isomers that are mirror images of each other → optical isomers
he mirror images will be non super imposable to each other

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8
Q

what is the effect of different arrangements of molecules

A
  • the orientation can lead to dramatically different effects on biological organisms which is why we want to separate them
    • example of thalidomide
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9
Q

what are enantiomers

A

each of a pair of molecules that are mirror images of each other
the different isomers are called enantiomers
enantiomers are non-superimposable

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10
Q

what is plane polarised light

A

light in one plane → travel in one direction

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11
Q

what is a racemic mixture

A

enantiomers are made in a 50/50 mix which is known as a racemic mixture

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12
Q

what is the effect of individual enantiomers on plane polarised light

A

individual enantiomers can cause plane polarised light to rotate either to the right or to the left
If single enantiomer is produced

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13
Q

what is the effect of a racemic mixture on plane polarised light and why

A

plane polarised light has no effect on a racemic mixture because there is an equal mix of left and right enantiomers

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14
Q

what is the SN1 mechanism

A
  • takes place in two steps
  • R- represents alkyl groups
  • central carbon has 4 different groups so has a chiral centre
    • needs to have a chiral centre or it wont work
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15
Q

recall/draw the steps of the SN1 mechanism with the example of 2-bromo,2-methylpropane

A
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16
Q

what happens if the intermediate is planar in the SN1 mechanism

A

if the intermediate (carbocation has lost a bond) is planar, the nucleophile can either attack from above or below
- if the attack happens from above it will be a different shape compared to if the attack happens from below
- different arrangement depending on where the nucleophile has attacked from

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17
Q

what happens if bonds are added/lost from the molecule

A

when bonds are added/lost the shape changes (show this when drawing mechanisms)

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18
Q

what is the product of the SN1 mechanism

A

racemic mixure
forms enantiomers which means they can rotate plane polarised light which is known as optical activity

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19
Q

what is the evidence for the SN1 mechanism

A

the product of the SN1 mechanism wont have an effect on plane polarised light

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20
Q

what is a transition state

A

one group joins as another group comes off

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21
Q

draw the SN2 mechanism with the example of 2-bromo,2-methylpropane

A

occurs in one step

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22
Q

what is the product of the SN2 mechanism

A

one product
doesnt have a racemic mixture
product will rotate plane polarised light

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23
Q

which mechanism does a tertiary carbocation undergo

A

tertiary carbocation should undergo SN1 mechanism
tertiary carbocation is most stable so can only exist as a carbocation for a short period of time

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24
Q

which mechanism des primary carbocations undergo

A

so for SN2 can only occur with a primary or secondary carbocation as they are less stable

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25
Q

what is the functional group for carbonyl compounds

A
  • carbonyl compounds → contain carbonyl group C double bond O
  • gives them the functional group -CO
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26
Q

what are the most common carbonyl compounds

A

aldehydes and ketones

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27
Q

what does the -CO functional group allow carbonyl compounds to do

A

allows these molecules to form hydrogen bonds with water
this means that aldehydes and ketones are soluble in water as they can form hydrogen bonds with water molecules

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28
Q

how do hydrogen bonds form between carbonyl compounds and water

A

a hydrogen bond forms between a lone pair of electrons on the oxygen atom on the C=O functional group and a positive dipole region on a hydrogen atom

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29
Q

why cant carbonyl compounds form hydrogen bonds between other carbonyl compounds

A

aldehydes and ketones dont have a slightly positive hydrogen atom, therefore they dont form hydrogen bonds between molecules

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30
Q

what forces exist between carbonyl compounds

A

only london forces are present between these molecules

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31
Q

how can aldehydes be produced

A

they are produced from the initial oxidation and distillation of primary alcohols

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32
Q

what is the structure of aldehydes

A
  • They have a carbonyl group on a carbon atom at the end of the chain
    • this carbon is only attached to one other carbon atom
  • this gives them the functional group -CHO
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33
Q

draw an example of the functional group of aldehydes

A
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34
Q

how can carboxylic acid be produced

A

aldehydes can be oxidised further in the presence of acidified potassium dichromate (VI) to produce carboxylic acids

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35
Q

what is the structure of ketones

A

have a carbonyl group on a carbon that is attached to two other carbon atoms
-C=O functional group

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36
Q

how can ketones be produced

A

produced from the oxidation of secondary alcohols with acidified potassium dichromate (VI)

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37
Q

draw an example of a ketone

A
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38
Q

write the equation for the oxidation of ethanol to form an aldehyde using displayed formula

A
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39
Q

write the equation of ethanal (Aldehyde) being further oxidised under reflux to form a carboxylic acid

A
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40
Q

write the equation for the oxidation of a secondary alcohol (propan-2-ol) to a ketone

A
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41
Q

what can potassium dichromate (VI) be used for

A

used as an oxidising agent for oxidation of alcohols

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42
Q

how do you know when an alcohol has undergone oxidation

A
  • potassium dichromate (VI) is reduced when alcohol is oxidised
    • results in a colour change from orange to green
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43
Q

what can be used to test for aldehydes

A

tested using tollens reagent or fehlings solution

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44
Q

how can fehlings solution be used to test for aldehydes

A
  • fehlings/tollens acts as an oxidising agent
  • a few drops of fehlings is added and the test tube is gently warmed
  • if aldehyde present a red precipitate will form
  • if ketone present → solution remains blue
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45
Q

how can you test for aldehydes using tollens reagent

A
  • if aldehyde present a layer of silver will form on the walls of the test tube
  • if ketone present → remains colourless
46
Q

how can reactions that produce carbonyl compounds from alcohols be reversed

A

oxidation reactions which produce carbonyl compounds from alcohols can be reversed via reduction reactions

47
Q

what reducing agent can be used to reverse the oxidation of alcohols

A

lithium tetrahydridoaluminate (III) aka aluminium hydride (LiAlH4) is used as a reducing agent
- example of nucleophilic addition reaction

48
Q

what solvent does the reduction reaction used to reverse the oxidation of alcohols require and why

A
  • LiAlH4→ very reactive
    • will react violently with water and alcohols
    • so reaction is carried out in dry ether solvent
49
Q

recall the steps of the reduction reaction used to reverse the oxidation of alcohols

A
  • LiAlH4 provides the H:- nucleophile
  • first the salt is formed
  • then dilute acid is added to release the alcohol from the salt
  • reducing agent represented by [H] in the equation
50
Q

write the equation using displayed formula of the reduction of aldehydes to form an alcohol using the example of ethanol

A
51
Q

show the mechanism for the production of a hydroxynitrile from an aldehyde- what kind of reaction is it

A

nucleophilic addition can also occur with the :CN- nucleophile
causes carbon chain to be extended by one carbon atom

52
Q

what substance is usually used to provide the nucleophile instead of HCN in the mechanism to produce a hydroxynitrile and why

A
  • KCN (potassium cyanide) is often used to provide the nucleophile instead of hydrogen cyanide (HCN)
    • bc HCN is hard to store
    • is a toxic gas
    • reacts to produce dangerous by-products
      also because theres a strong bond between H and CN whereas for KCN theres weak bonds so gives a greater supply of CN- ions
52
Q

what do hydroxynitriles contain

A

hydroxynitriles contain a chiral carbon centre so optical isomers of the product are produced

53
Q

why does the mechanism to form hydroxynitriles from aldehydes cause different enantiomers to be produced

A

the :CN- nucleophile can attack from either above or below the planar double bond

54
Q

what is the iodoform test used to identify

A
  • uses triiodomethane
  • used to identify CH3CO- groups
  • can be used to identify aldehydes and ketones
55
Q

how is the iodoform test carried out

A
  • iodine solution added to unknown sample
  • then sodium hydroxide solution is added until the colour created by iodine is removed
56
Q

what does a positive result for the iodoform test look like

A

positive result (ketone or aldehyde present) → pale yellow precipitate formed which is known as triiodomethane (CHI3)

57
Q

what can the 2,4-dinitrophenylhydrazine test be used to test for

A

can be used as a test for the carbonyl functional group

58
Q

what occurs when ketones or aldehydes are reacted with 2,4-DNPH

A

when aldehydes and ketones are reacted with 2,4-DNPH → yellow, orange or reddish-orange precipitate will form

59
Q

What is the mtp of carbonyl compounds

A

carbonyl compounds have a sharp melting point → melt over narrow range of temps

60
Q

how can mtp be used t identify carbonyl compounds

A
  • 2,4-DNPH added to the compound so that a precipitate forms
  • the solid is then purified by recrystallisation (crystalise again)
  • mtp of the pure crystals can be formed and compared to the mtp of all 2,4-dinitrophenylhydrazones of all common aldehydes and ketones in a data booklet
61
Q

what is the functional group for carboxylic group

A

carboxylic acids can be identified by the -COOH functional group
also contains a carbonyl group C=O and an -OH acid group

62
Q

what is the suffix for carboxylic acids

A

suffix -anoic acid

63
Q

draw an example of a carboxylic acid with 2 carbons

A
64
Q

what are the two ways carboxylic acids can be produced

A
  • carboxylic acids can be prepared by oxidising primary alcohols or aldehydes under reflux using potassium dichromate (VI)
  • can also be produced by the hydrolysis of nitrile compounds
65
Q

what allows carboxylic acids to form hydrogen bonds

A

-COOH functional group allows carboxylic acids to form H bonds between each other

66
Q

why are carboxylic acids soluble in water

A

they can also form hydrogens bonds with water → meaning they’re soluble in water

67
Q

what causes the trend in solubility of carboxylic acids

A
  • as chain length inc, solubility dec as CH2 groups don’t form hydrogen bonds with water
    • only form london forces with water
68
Q

why do carboxylic acids have even higher mtp and mpts than alcohols, aldehydes and ketones

A

C=O and O-H parts of the functional group of carboxylic acids can form hydrogen bonds between molecules

69
Q

draw an example of hydrogen bonding between 2 carboxylic acid molecules

A
70
Q

recall the reactions that carboxylic acids can undergo

A

reduction
neutralisation with bases
acylation
esterification

71
Q

what can carboxylic acids be reduced to and with what reducing agent

A

reducing agent LiAlH4 can be used to produce primary alcohols from carboxylic acids
LiAlH4 provides the H:- nucleophile

72
Q

how are carboxylic acids reduced to primary alcohols

A
  • carboxylic acids are first reduced to aldehydes
  • however, aldehydes cant be isolated from this reaction as they’re more reactive than carboxylic acids
    • so they’re immediately reduced further to primary alcohols
73
Q

draw the displayed formula for the reduction of carboxylic acids to a primary alcohol using the example of ethanol

A
74
Q

what is the reaction of carboxylic acids and a base

A

produced salt and water
carboxylate salt
R-COONa + H2O
R-carbon chain

75
Q

what is a carboxylic acid derivative

A

carboxylic acids have derivative molecules where the -OH group is replaced by another group

76
Q

what is acyl chloride an example of

A

Acyl chlorides are an example of a derivative of carboxylic acid

77
Q

why do acyl chlorides react violently

A

that reacts violently due to the very polar -COCL group

78
Q

draw an example of the acyl chloride functional group

A
79
Q

how can acyl chlorides be produced from carboxylic acids

A

acyl chlorides can be produced by the reaction between carboxylic acids and phosphorus (V) chloride

80
Q

write the equation for the reaction to produce an acyl chloride from ethanoic acid

A
81
Q

how can esters be produced from a carboxylic acid + conditions

A

carboxylic acids can react with alcohols in the presence of a strong acid catalyst to form esters
- conc. sulfuric acid can be used as an acid catalyst
- this reaction is called esterification
- carried out under reflux

82
Q

using the example of methanol and ethanoic acid, draw the reaction to produce an ester using displayed formula

A
83
Q

what is the simplified steps of producing an ester from an alcohol and carboxylic acid

A

remove -OH group from the acid and the hydrogen from alcohol to make water

then join the acid and alcohol together

84
Q

what are the properties of esters

A
  • esters are sweet smelling compounds
    • used in food flavourings and perfumes
  • they have low bpts and are good solvents for polar molecules
85
Q

how are esters named

A

beginning of alcohol name
beginning of carboxylic acid name with -anoate ending
e.g an ester made from ethanol and propanoic acid would be called ethyl propanoate

86
Q

how are acyl chlorides named

A

have the suffix -oyl chloride, stem of their name representing the longest chain of carbon atoms
e.g butanoyl chloride

87
Q

what is the functional group of esters

A

-COO

88
Q

what is the functional group of esters

A

-COO

89
Q

acyl chloride + water

A

carboxylic acid

90
Q

acyl chloride + alcohol

A

ester

91
Q

acyl chloride + ammonia

A

amide

92
Q

draw the functional group for an amide

A
93
Q

acyl chloride + amine

A

N-substituted amide

94
Q

what is an N-substituted amide

A

N-substituted amide has another carbon group attached to the nitrogen (instead of hydrogen)

95
Q

Through what mechanism do acyl chlorides react

A
  • acyl chlorides react via nucleophilic addition- elimination reactions
    • the addition of a nucleophile in these reactions leads to the elimination of a product under aqueous conditions
96
Q

how can you convert esters back into alcohols

A

ester hydrolysis
convert esters back into alcohols and carboxylic acids which is done by adding water

97
Q

what is the reaction of esters and water under acidic conditions- draw the equation

A

reverse reaction → turns ester back into alcohol and carboxylic acids by adding water

98
Q

what is the reaction of esters and a base (alkaline conditions)- draw the equation

A
  • carboxylic acid produced can react further with a base to form a salt
  • this process is called saponification
  • these salts have hydrophobic and hydrophilic properties
99
Q

how are condensation polymers formed

A

formed when a water molecule is removed from the species of a reaction

100
Q

how are polyesters formed

A

from a reaction between a dicarboxylic acid and a diol which produces an ester linkage, -C(double bond)OO-

101
Q

why are polyesters biodegradeable

A
  • polyesters can be broken down through hydrolysis due to the polarity
  • therefore they’re biodegradable
    • can be broken down easily by naturally occurring water or moisture
    • so they can be put into landfill where they will break down gradually
102
Q

what is solid sodium carbonate used to test for

A

acids

103
Q

what is PCL5 used to test for

A

OH group

104
Q

why may the product for the reaction of a molecule with a chiral centre lack optical activity

A

the intermediate is planar so the attacks can happen from above or below
leading to the formation of a racemic mixture

105
Q

which compound is oxidised by ammoniacal silver nitrate in the test using tollens reagent

A

aldehydes

106
Q

how do you test for a carbonyl compound using tollens reagent

A

is an oxidation reaction
add silver nitrate to a test tube
add 2M dilute ammonia solution drop wise until the precipitate dissolves
then add 10 drops of the carbonyl compound and shake
warm the contents in a water bath
silver mirror forms in the presence of an aldehyde

107
Q

how do you carry out the test for aldehydes using benedicts solution

A

is an oxidation reaction
add a few drops of the aldehyde to water in a boiling tube
add the same volume of benedicts solution as the volume water
colour change blue to brick red

108
Q

what are the conditions and reagents for oxidising an alcohol

A

reflux
add dilute sulfuric acid to a warm solution of potassium dichromate
(acidic conditions)

109
Q

How can a polyester be produced

A

molecule with OHand COOH group
Or dicarboxylic and diol

110
Q

What additional force can carboxylic acids form

A

can form dimers that are even stronger than all of the intermolecular forces because all of the Os and Hs in the COOH functional group can have a slight charge
Carboxylic acids can form London forces, hydrogen bonds and dimers

[OBSELETE] S - Chem (19 decks)

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