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Chemistry > TOPIC 17 : ORGANIC CHEMISTRY II > Flashcards

TOPIC 17 : ORGANIC CHEMISTRY II Flashcards

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1
Q

Explain what is meant by a chiral molecule and say how you would recognise an asymmetric carbon atom.

A

A chiral molecule is one that has no plane of symmetry. An asymmetric carbon atom is one that is attached to 4 different groups.

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2
Q

Why doesn’t a racemic mixture have any effect on the plane of polarisation of plane polarised light?

A

It is a 50/50 mixture of the two enantiomers. One of these is rotating the plane
of polarisation anti-clockwise, and the other is rotating it by exactly the same amount clockwise. They cancel each other out, so there is no overall effect on the light.

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3
Q

Define structural isomer

A

Same molecular formula different structural formulae

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4
Q

Define Chain isomers

A

Compounds with the same molecular formula but different structures of the carbon skeleton

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5
Q

Define Position isomers

A

Compounds with the same molecular formula but different structures due to different positions on the same functional group on the same carbon skeleton

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6
Q

Define functional group isomers

A

Compounds with the same molecular formula but with atom arranged to give different functional groups

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7
Q

What causes positional isomerism

A

Functional groups found at different positions on a chain

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8
Q

What are stereoisomers

A

Stereoisomers have the same structural formulae but have a different spatial arrangement of atoms

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9
Q

What causes chain isomerism

A

Different chain lengths due branching

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10
Q

What causes functional group isomerism

A

The position of atoms causes different functional groups eg = ketones and aldehydes

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11
Q

Explain how geometric isomerism arises

A

When there is a double bond between Carbons causing restricted rotation around the double bond and two different groups/atoms attached to both ends of the restricted double bond

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12
Q

What are the two types of stereoisomers

A

Geometrical isomerism ( E/Z) and optical isomerism

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13
Q

What is a Z isomer how do we determine if an isomer is a Z isomer

A

A Z isomer is when the priority groups on either side are on the same side

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14
Q

What is an E isomer how do we determine if an isomer is an E isomer

A

If the priority groups are on opposite sides then it is an E isomer

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15
Q

What is a priority group

A

The atom with the larger atomic proton number

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16
Q

When does optical isomerism occur

A

Occurs in carbon compounds with 4 different groups of atoms attached to a carbon

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17
Q

What shape are optical isomers

A

Tetrahedral

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18
Q

Define a racemic mixture

A

A racemic mixture is a mixture containing equal amounts of two enantiomers (optical isomers) that rotate plane polarised light in opposite directions by the same amount

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19
Q

What are enantiomers

A

Optical isomers

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20
Q

What is special about optical isomers

A

They have similar chemical and physical properties but rotate plane polarised light by the same amount in different directions

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21
Q

How is a racemate mixture formed use an example

A

Nucleophilic addition of HCN to aldehydes and unsymmetrical ketones from both sides forms a racemate

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22
Q

What is optical activity

A

When an optical isomer rotates plane polarised light

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23
Q

What is a chiral molecule

A

A carbon atom that has 4 different groups attached

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24
Q

Give an example of how optical activity provides evidence for SN1 mechanisms. DESCRIBE the mechanism for 2 bromo-butane reacting with a OH- ion

A

The Br breaks away from the haloalkane to form a carbocation intermediate

The OH- ion can attach from other side resulting in different enantiomers and a racemate forms

Because a racemate forms they will be no optical activity in the products proving SN1 mechanisms

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25
Give an example of how optical activity provides evidence for SN2 mechanisms Describe the mechanism for 2 bromo- butane with a OH - ion
Give an example of how optical activity provides evidence for SN2 mechanisms Draw the mechanism for 2 bromo- butane with a OH - ion In an SN2 mechanism there is no intermediate species formed The OH- attacks the carbon and the bromine breaks off If the reactant was chiral than during the reaction the opposite enantiomer would form
26
How else can we get a racemic mixture? Draw the mechanism
We can form a racemate by the electrophilic addition of HBr to an unsymmetrical alkene
27
What test would you use to distinguish between hexane and hex-1-ene ? Give the results of the test for each substance
Bromine water Bromine water is an orange solution of bromine and it becomes colourless when an alkene is present as alkenes decolourise bromine water
28
What is meant by non-superimposable
Cannot be placed above one another and look the same
29
Define plane polarized monochromatic light
Light that only oscillates in one plane and is one colour
30
State how separate samples of 2 - enantiomers could be distinguished in a laboratory
Observe the directions they rotate plane polarised light
31
What is formed during a reaction undergoing SN1
Carbocation intermediate
32
What is involved during an SN2 mechanism
Two molecules are involved, the nucleophile attacks the carbon cation when the halogen breaks off
33
How can we separate samples of optical isomers be distinguished
Pass plane polarized light through the isomers and the isomers will rotate the plane polarized light in opposite directions.
34
Why do alcohols have higher boiling points than alkanes
Alcohols have higher boiling points than an alkane with the same number of carbon atoms due to hydrogen bonding.
35
What is formed from the oxidation of a primary alcohol
You get an aldehyde if you distill or a carboxylic acid if you reflux or oxidise the aldehyde
36
What is formed from the oxidation of a secondary alcohol
ketone
37
What is formed from the oxidation of a tertiary alcohol
They do not oxidise
38
What reagent is used to oxidise the alcohols or aldehydes
Potassium dichromate (K2 Cr2 O7)
39
What does the chromium species get reduced to and state the colour change
The orange dichromate ion (Cr2O72-) is reduced to the green Cr3+ ion
40
How would you prepare to form an aldehyde from a primary alcohol
Add potassium dichromate solution K2Cr2O7 to excess alcohol and distill off the aldehyde as soon as it forms
41
Describe what happens when a reaction mixture is refluxed and why it is necessary in this case for complete oxidation to ethanoic acid
A mixture of liquids are heated to boiling point for a long time Vapour is formed which escapes from the liquid mixture and condenses and returns to the liquid mixture Any ethanol and ethanal that evaporated can be oxidised
42
What are the circumstances for us including numbers to show the position of the double bond in ketones
When ketones have 5 CARBONS OR MORE you need to add a number to show the position of the double bond eg pentan-2-one
43
When is the prefix oxo used
It is used for compounds that contain a ketone group in addition to a carboxylic acid or aldehyde attached
44
What reagents are used in oxidation and how can they easily be expressed
Potassium dichromate it can easily be expressed as [O]
45
What reagents are used in reduction and how can they easily be expressed
LiAlH4 and it can easily be expressed as [H]
46
Why must LIALH4 be dissolved in dry ether
LiALH4 reacts violently with water and alcohols and the dry ether prevents this.
47
Describe the solubility of small carbonyls
Small carbonyls are soluble in water because they can form hydrogen bonds in water
48
Describe the solubility of pure carbonyls
They cannot hydrogen bond but bonds instead by permanent dipole bonding
49
What are the two other reagents that can oxidise an aldehyde into a carboxylic acid and what are the conditions,reaction and observations of each
Tollens Reagent= Conditions= heat gently Reaction and observation = aldehydes only are oxidised by tollens reagent into carboxylic acids and the silver ions are reduced into silver atoms and a silver mirror is produced, Ketones result in no change Fehling's solution= Conditions= heat gently Reactions= aldehydes only are oxidised by fehling's solution into a carboxylic acid and the copper ions are reduced to copper oxide Observation= BLUE CU 2+ ions in solution change to a red precipitate of Cu2O. KETONES DO NOT REACT
50
What test do we use to identify carbonyl compounds and describe the process
Brady's reagent (2,4, DNP) - product is an orange precipitate Rinse the carbonyl with brady's reagent Filter precipitate Recrystallise the precipitate using maximum amount of hot ethanol Measure the melting and boiling temperature and dry purified product Refer to data to determine carbonyl
51
A mechanism of the reaction between an aldehyde and hydrogen cyanide name what type of mechanism this is and condiitons
Nuclophilic addition - Conditions= Room temperature and pressure, HCN in presence of KCN
52
Why is Hydrogen cyanide in the presence of KCN
The KCN increases the concentration of the CN- ion
53
What is a nucleophile
Donates an electron pair, negatively charged and is attracted to areas of low electron density
54
What carbonyls can react with iodine in the presence of sodium hydroxide
Only carbonyls with a methyl group next to the C=O bond can do this reaction. Ethanal is the only aldehyde that reacts. Methyl ketones mostly react
55
Write the equation for ethanal + iodine sodium hydroxide and state the product formed
CH3COCH3 +3I2 +4NaOH > CHI3 + 3NaI + 3H2O The product formed is CHI3 which is a yellow precipitate with an antiseptic smell
56
What is the name of the salt formed from carboxylic acid and the name the salt from ethanoic acid
A carboxylate, ethanoic acid= ethanoate
57
Describe the solubility of carboxylic acids in water
Small carboxylic acids can dissolve in water (up to butanoic acid) after this solubility decreases.
58
Describe the acidity of carboxylic acids
They are weak acids in water and only partially dissociate
59
What is a dimer
Two carboxylic acids bonded together by a covalent bond
60
Explain how the ability of ethanoic acid to dimerise affects its boiling point
The boiling point will be higher as the molecule will be larger and contain twice the number of electrons meaning greater london forces and more energy is required to break them
61
Suggest an explanation for why sodium ethanoate is a solid at room temperature while ethanoic acid is a liquid
Sodium ethanoate is an ionic lattice so will have strong electrostatic forces of attraction between oppositely charged ions. Lots of energy is required to overcome this attraction. Ethanoic acid has intermolecular forces between molecules which require less energy to overcome
62
What are the three ways you can prepare a carboxylic acid
Full oxidation of primary alcohols, Oxidation of aldehydes, hydrolysis of nitriles
63
Name the reagent, conditions and the reaction of the hydrolysis of nitriles
Reagent= Dilute HCL/sulfuric acid Conditions= Heat under reflux Reaction = Nitrile > Carboxylic acid
64
What is formed when you react an acid + metal
Salt + hydrogen
65
What is formed when you react an acid + alkali
Salt + water
66
What is formed when you react an acid + carbonate
Carbon dioxide + salt + water
67
What is the only carboxylic acid that can be oxidised by using oxidizing agents and what does it form
Methanoic acid is the only one as its structure is effectively an aldehyde group it forms carbonic acid which decomposes to carbon dioxide
68
Describe the reaction between carboxylic acids and phosphorus chloride and describe the conditions and observations and write an equation for the reaction of ethanoic acid reacting with phosphorus chloride
Reaction = Carboxylic acid > acyl chloride Conditions= Room temperature Observations= Misty fumes of HCL Equation= CH3COOH + PCL5 > POCL3 + HCL+ CH3COCL
69
What is formed when you react a carboxylic acid with alcohol and what is special about this reaction and the conditions
Carboxylic acid + alcohol > salt + water It requires a strong acid catalyst (H2SO4), the reaction is slow and needs to be heated under reflux it is also reversible
70
How do you name an ester
The part ending in yl comes from the alcohol that formed it | The part ending in anoate comes from the carboxylic acid
71
How can esters be hydrolysed
They can be hydrolysed either by heating under reflux with acid or NaOH
72
Name one way an ester can be hydrolysed and state the conditions, reagents and a reaction equation using the ester ethyl propanoate
Heating under reflux with dilute NaOH Ethyl propanoate + NaOH > sodium propanoate + ethanol This reaction is not reversible and goes to completion
73
Name another way an ester can be hydrolysed and state the conditions, reagents and a reaction equation using the ester ethyl propanoate
Heating under reflux with dilute HCL acid and heat under reflux Ethyl propanoate + water >> Propanoic acid + ethanol
74
What are the conditions and reagents and products for reacting an acyl chloride with water and state the observation
``` Products= Carboxylic acid Reagent = water Conditions= room temperature Observation= Steamy white fumes of HCL ```
75
What are the reagents,conditions and products for reacting an acyl chloride with alcohol and state the observation
``` Products= Ester Reagent = alcohol Conditions= room temperature Observation= Steamy white fumes of HCL ```
76
What are the reagents,conditions and products for reacting an acyl chloride with ammonia and state the observation
``` Products= primary amide Reagent = ammonia Conditions= room temperature Observation= white smoke of NH4Cl is give off ```
77
What are the reagents,conditions and products for reacting an acyl chloride with primary amines
``` Products= Secondary amide Reagent = Primary amine Conditions= room temperature Observation= Steamy white fumes of HCL ```
78
What are the two types of polymerisation
Addition polymerisation and condensation polymerisation
79
How to produce polyesters
1. diol + diacarboxylic acid > Water + polyester | 2. diol + diacyl dichloride > HCL + polyester
80
Why Is chloroethanoic acid more acidic than ethanoic acid
Chlorine is more electronegative and therefore withdraws the electrons from COOH decreasing COOHs electron density and less negative so it becomes more stable and therefore chloroethanoic acid is more acidic
81
Why does increasing chain length of a carboxylic acid mean it is less acidic
Increasing the chain length increases electron releasing alkyl groups attached which make the COOH more negative and less stable so it is weaker
82
What can polyesters be hydrolysed by
1. Acid or alkali 2. With HCL a polyetser will be hydrolysed and spilt up into the original dicarboxylic acid and diol 3. With NaOH a polyester will be hydrolysed and split up into the diol and dicarboxylic acid salt

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