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Chemistry Alevel OCR > 6.1 Aromatic Compounds, Carbonyls And Acids > Flashcards

6.1 Aromatic Compounds, Carbonyls And Acids Flashcards

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1
Q

What is a benzene derivative?

A

-a benzene ring that has undergone a substitution reaction

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2
Q

What is a substitution reaction?

A

-where a group or atom is exchanged for another group or atom in a chemical reaction

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3
Q

What is an ester?

A

—esters have the functional group -COO
-they are carboxylic acid derivatives where the H from the acid has been replaced with an alkyl chain

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4
Q

How are esters named?

A

-named after the alcohol and carboxylic acid from which they are formed
-the first part of the name comes from the alkyl chain with a carbon atom bonded to only one oxygen atom
-the second part comes from the alkyl chain containing the C=O carbon atom
-it is followed by the suffix -oate

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5
Q

Name this ester

A

-methyl ethanoate

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6
Q

What is esterification?

A

-the chemical reaction used to make an ester

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7
Q

Describe the conditions needed for the esterification of a carboxylic acid with an acid catalyst

A

-to prepare a small ester- alcohol and a carboxylic acid are heated gently in the presence of a sulfuric acid (H2SO4) catalyst,this is a reversible reaction and has a slow rate of reaction- separated by distillation as the ester is volatile, distillation needs to be quick to prevent reverse reaction from occurring

-to prepare larger esters-alcohol and carboxylic acid with sulfuric acid catalyst heated under reflux until equilibrium has been established-the ester can be separated using fractional distillation

->this method of preparation of an ester is not suitable for phenol or its derivatives as the rate of reaction is too slow

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8
Q

Draw out the reaction of methanol with ethanoic acid using their structural formulas and name the product

A
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9
Q

What are 3 properties of esters ?

A

-sweet smelling compounds used in food flavourings and perfumes
-low boiling points
-good solvents for polar molecule

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10
Q

What is an acid anhydride?

A

-an acid derivative
-more reactive than a similar carboxylic acid
-made by the removal of a water molecule from two carboxylic acid molecules

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11
Q

What does anhydride mean?

A

-without water

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12
Q

Describe esterification of acid anhydrides with alcohols

A

-acid anhydrides will react with alcohols including phenols and its derivatives to make an ester
-it is an addition-elimination mechanism
-not reversible -therefore has a higher yield than using carboxylic acid
-slow rate of reaction that can be increased by gently warming reaction mixture

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13
Q

Draw out the reaction of ethanoic anhydride and methanol and name the products

A
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14
Q

Define hydrolysis

A

-a chemical reaction where water causes the breaking of bonds. In a decomposition reaction

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15
Q

What is the name of the reverse reaction of esterification?

A

-hydrolysis
-esters can undergo hydrolysis to form an alcohol

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16
Q

What happens when an ester undergoes hydrolysis in acidic conditions?

A

-When esters are refluxed with a catalyst of hot aqueous acids, such as dilute sulfuric acid or dilute hydrochloric acid, the ester will decompose reversibly into an alcohol and a carboxylic acid.

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17
Q

What happens when an ester undergoes hydrolysis in alkaline conditions?

A

-Alkaline chemicals are bases that can dissolve in water: When an ester is refluxed with a hot aqueous alkali, such as potassium hydroxide or sodium hydroxide, it will decompose into an alcohol and a carboxylate salt. This reaction is not reversible.
Alkaline hydrolysis of esters is used to make soaps, therefore it is also called saponification

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18
Q

Draw out the hydrolysis reaction between ethyl propanoate and sodium hydroxide name the products

A
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19
Q

Define a base

A

A chemical that will react with an acid

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20
Q

What is the carboxylic acid functional group?

A

-COOH

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21
Q

How do you name a carboxylic acid?

A

-remove the e from the end of the name of the alkane that has the same number of carbons in its longest carbon chain
-add the suffix -anoic acid

E.g-a carboxylic acid containing 4 carbon atoms would be called butanoic acid

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22
Q

How are carboxylic acids prepared?

A
  • by the oxidation of primary alcohols or aldehydes under reflux
    -acidified potassium dichromate (VI) used as the oxidising agent
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23
Q

Are carboxylic acids soluble?

A

-the -COOH functional group allows carboxylic acid molecules to form hydrogen bonds between each other
-they can also form hydrogen bonds with water meaning they are soluble in water

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24
Q

What happens to the solubility of carboxylic acids as their chain length increases?

A

-as chain length increases their solubility decreases
-as CH2 groups do not form hydrogen bonds with water as they are not polar
-so as more of the molecule becomes non-polar solubility will decrease

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25
Q

What type of acid is a carboxylic acid?

A

-a weak acid as they partially ionise in solution releasing the H+ ion from the carboxylic acid group forming a carboxylate ion

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26
Q

Do carboxylic acids react with metals?

A

-yes they will react to make hydrogen and a metal salt
-the name of the salt is generated from the acid
-the suffix of the acid changes from -oic acid to -oate
E.g- sodium+ethanoic acid —> sodium ethanoate+hydrogen

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27
Q

What can metal oxides be classified as?

A

-metal oxides react with acids and can therefore be classified as bases

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28
Q

What is made when carboxylic acids react with metal oxides?

A

-water and a metal salt
-e.g. magnesium oxide+methanoic acid —->magnesium methanoate+water

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29
Q

What will be made when a carboxylic acid reacts with a metal hydroxide?

A

-group one metal hydroxides are soluble bases they will react with carboxylic acids to make water and a metal salt
E.g.potassium hydroxide+propanoic acid—->potassium propanoate+ water

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30
Q

Do carboxylic acids react in neutralisation reactions?

A

-carboxylic acids are weak acids and therefore react with bases in a neutralisation reaction to produce a salt and water

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31
Q

What will be made when metal carbonates react with carboxylic acids?

A

-water , carbon dioxide and a metal salt
-they will also react with metal hydrogencarbonates to form salt, water and carbon dioxide

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32
Q

What is the acyl chloride functional group?

A

-COCl

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33
Q

What are acyl chlorides?

A

-carboxylic acid derivatives where the -OH of the acid group has been replaced with a chlorine atom
-very reactive due to very polar -COCl group

34
Q

How do you name acyl chlorides?

A

-the longest chain of carbon atoms is the stem
-add the suffix -oyl chloride

35
Q

How are acyl chlorides produced?

A

-add SOCl2
-the products are acyl chloride, sodium dioxide and hydrogen chloride
-separate the acyl chloride from the reaction mixture using distillation

36
Q

Write out the equation for the formation of ethanoyl chloride

A
37
Q

How are acyl chlorides used to form esters?

A

-acyl chlorides will react with alcohols to make an ester
-this method of ester production is not reversible so has a higher yield than using a carboxylic acid

38
Q

Write out the chemical equation that shows the formation of ethyl ethanoate from an acyl chloride?

A

CH3COCl + CH3CH2OH—> CH3COOCH2CH3 +HCl

39
Q

What do phenols react with to make an ester?

A

-phenols are not readily esterified by carboxylic acids
-to make an ester from phenols acyl chloride must be used
-this reaction is violent and produces corrosive fumes of HCl

40
Q

How do small acyl chlorides react with water ?

A

-when a small acyl chloride is added to water it quickly hydrolyses to produce a carboxylic acid
-this is a very exothermic reaction and misty fumes of HCl are given off

41
Q

Write down the equation for the reaction of ethanoyl chloride with water?

A

CH3COCl +H2O —> CH3COOH +HCl

42
Q

How are primary amides produced from acyl chlorides?

A

-when an acyl chloride reacts with ammonia a primary amide is produced
-e.g. to produce ethanamide ethanoyl chloride is added to a concentrated ammonia solution
-this quickly produces a mixture of solid ammonium chloride and ethanamide-observed as white smoke
-some products remain in a colourless solution

43
Q

Write down the reaction between ethanoyl chloride and ammonia

A

CH3COCl + 2NH3 —> CH3CONH2 +NH4Cl

44
Q

What does an acyl chloride form when it reacts with a primary amide?

A

-a secondary amide (where the nitrogen has one hydrogen atom directly bonded to it) is produced as well as HCl
-the nitrogen atom also has 2 organic groups attached and it often called an N-substituted amide

45
Q

What does ethanoyl chloride and react with etylamine to produce?

A

-ethanoyl chloride and a cold concentrated solution of ethylaminne react to produce a white solid compound of N-ethylamine

CH3COCl + CH3CH2NH2 —>CH3CONHCH2CH3 +HCl

46
Q

What is a phenol?

A

-a class of aromatic compounds where a hydroxyl group is directly attached to the aromatic ring
-phenol is the first member of a type of aromatic compounds where a hydroxyl group is attached directly to an aromatic ring
-if the hydroxyl group is attached to an alkyl chain on the aromatic ring the compound is no longer a phenol derivative. It would be described as an AROMATIC ALCOHOL

47
Q

What type of acid is a phenol?

A

-a weak acid that partially dissociates in water

48
Q

What is the chemical equation of the reaction between a phenol and water?

A
49
Q

What is the chemical equation between a phenol and sodium hydroxide?

A
50
Q

What shows that phenols are weak acids?

A

-they are an acid as they react with bases
-they will undergo a neutralisation reaction with NaOH as it is a strong base
-they will not react with carbonates as carbonates are weak bases therefore phenols are weak acids

51
Q

Why are phenols more reactive than benzene ?

A

-as the lone pair of electrons from the p-orbital of the oxygen of the hydroxyl group are donated into the benzene ring structure to the π-system
-the lone pair becomes part of the delocalisation this increases electron density of the ring making it more susceptible to attack from electrophiles

52
Q

What is the directing effect?

A

-how a functional group attached directly to an aromatic ring affects which carbon atoms are more likely to undergo substitution

53
Q

What is the reaction of a phenol and bromine (bromination)?
What does it form ?
What is the equation ?

A

-phenol will undergo an electrophilic substitution reaction with bromine water at room temperature. It is a triple substitution
-the resulting product is a white precipitate of 2,4,6-tribromophenol -which smells like antiseptic
EQUATION
C6H5OH + 3Br2 —>C6H2Br3OH +3HBr

54
Q

What is the reaction between dilute nitric acid and phenol (nitration)?
What is the equation?
What is formed?

A

-is an electrophilic substitution reaction, phenol will undergo a single substitution with dilute nitric acid (HNO3) at room temperature
EQUATION
C6H5OH +HNO3–>C6H4(NO2)OH +H2O
-the reaction forms a mixture of 2-nitrophenol and 4-nitrophenol

55
Q

Why is nitration of phenol unlike nitration of benzene?

A

-nitration of phenol does not require concentrated nitric acid or a sulphuric acid catalyst this is unlike the nitration of benzene

56
Q

What are two electron donating groups?

A

-OH and NH2
-these activate the benzene ring they push additional electrons into the π-system

57
Q

Where do electron donating groups direct electropphiles?

A

-electron donating groups such as OH and NH2 direct electrons to substitute at the carbon 2 and carbon 4 positions

58
Q

What directing effect is seen with electron withdrawing groups such as NO2?

A

-a 3-directing effect is seen when NO2 groups are directly attached to the aromatic ring
-as the nitro group withdraws electrons from the π- system and makes the rate of substitution highest on the third carbon atom

59
Q

Why are directing effects important?

A

-as they can be used to predict positions in which substitutions will take place
-important in organic synthesis as it allows you to control the structure of the products to maximise the desired product

60
Q

What are the general reaction steps in electrophilic substitution?

A

1-electrons above and below the plane of atoms in a benzene ring attract an electrophile
2-the electrophile accepts a pair of π electrons from the delocalised ring and makes a covalent bond (this is the rate-determining step)
3-a reactive intermediate is formed where the delocalised electrons have been disrupted
4-the unstable intermediate releases a H+ ion and the stable product is formed (this is the rapid step)

61
Q

Draw the general electrophilic substitution mechanism

A
62
Q

What is electrophilic substitution?

A

-a substitution reaction where an electrophile is attracted to an electron-rich atom or part of a molecule and a new covalent bond is formed by the electrophile accepting an electron pair

63
Q

What is a reaction mechanism?

A

-a model with steps to explain and predict a chemical reaction

64
Q

What is the catalyst and reagent in nitration of benzene?
How is the reaction carried out?

A

CATALYST- concentrated sulfuric acid
REAGENT-concentrated nitric acid
-the concentrated nitric acid and concentrated sulfuric acid are mixed together in a flask held in an ice bath. Then benzene
is added and a reflux condenser is set up, keeping the mixture at 50 C° to prevent further substitution reactions occurring

65
Q

What is the electrophile in the nitration of benzene?

A

NO2+ ion

66
Q

Write out the balanced chemical equation for the nitration of benzene
Draw out the mechanism
Include the equation for the generation of the electrophile and the regeneration of the catalyst

A

Equation for reaction-
C6H6 +HNO3 —>C6H5NO2 + H2O
Formation of electrophile-
HNO3+H2SO4–> NO2+ + HSO4- +H20
Regeneration of sulfuric acid catalyst
H+ + HSO4- —> H2SO4

67
Q

What are the 3 different halogen carriers that can be used for the chlorination of benzene?

A

-AlCl3
-FeCl3
-Fe

68
Q

What are the 3 halogen carriers that can be used for the bromination of benzene?

A

-AlBr3
-FeBr3
-Fe

69
Q

What is the mechanism for the bromination of benzene?
What is the equation for the formation of an electrophile ?
What is the equation for the regeneration of the halogen carriers (catalyst?)

A

FORMATION OF ELECTROPHILE-
Br2 + FeBr —> Br+ + FeBr4-
REGENERATION OF HALOGEN CARRIER
FeBr4- + H+ —> HBr + FeBr3

70
Q

Why unlike in alkenes does no reaction occur when benzene is shaking with bromine water?

A

-as benzene has a lower electron density between carbon atoms than an alkene
-when non-polar molecules approach the benzene ring there is not enough electron density between carbon atoms to induce a dipole and start a reaction

71
Q

What is the general mechanism for a chloroalkane undergoing a friedel crafts reaction?
Where iron(III) chloride is the catalyst and R stands for any alkyl group

A
72
Q

What are the conditions for acylation?

A

-reaction mixture held at 60 °C for 30mins under reflux

73
Q

What is the general mechanism for acylation?
Show show regeneration of AlCl3 catalyst
And generation of catalyst
R=alkyl group

A
74
Q

What is the experimental evidence for delocalised model of benzene instead of Kekulé model?

A

Resistance to reaction-you would expect Benzene to readily undergo addition reactions similar to alkenes. But benzene tends to undergo substitution of a hydrogen atom rather than addition reactions

Hydrogenation- hydrogenation is the addition of hydrogen to an unsaturated chemical. From enthalpy change of hydrogenation we see that benzene is 152kJmol-1 more energetically stable than predicted .

Bond lengths- X-ray diffraction techniques show that all 6 carbon bonds in benzene are 0.140 nm which is between the length of a C single bond and C double bond. Kekulé’s structure suggests that there should be 3 shorter carbon double bonds and 3 longer carbon single bonds however all 6 bonds are the same length

75
Q

Compare Kekulé’s model of benzene to delocalised model

A

-Kekulé- benzene is a six-membered ring, with alternating single and double bonds between the carbon atoms

-delocalised-each of the six carbon atoms donates one electron from its p-orbital
-these electrons combine to form a ring of delocalised electrons above and below the plane of the molecule. All bonds in the ring are identical so are the same length

76
Q

What is the 2,4-dinitrophenylhydrazine (2,4-DNPH) test for carbonyls?

A

-2,4-DNPH can be used as a qualitative test for the carbonyl functional group.
-When aldehydes and ketones are reacted with 2,4-DNPH a yellow, orange or reddish-orange precipitate will form; the exact colour depends on the identity of the compound.
- Alcohols and other molecules which don’t contain carbonyl groups do not produce a precipitate.
-Carbonyl compounds and their derivatives have sharp melting points, meaning they melt over a narrow range of temperatures. These compounds can have their melting points determined experimentally and their values compared to a databook to identify them.
-2,4-DNPH can be used to identify specific aldehydes/ketones by use of melting point data.
-The 2,4-DNPH is added to the compound so that a precipitate forms. The solid is then purified by recrystallisation.
-The melting point of the pure crystals formed can then be compared with the melting points of 2,4-dinitrophenylhydrazones of all the common aldehydes and ketones.

77
Q

What is the Tollen’s test used for ?
Why do the results occur?

A

-Aldehydes can be identified using Tollen’s reagent.
-If Tollen’s reagent is added to an aldehyde, a silver mirror will form
-If a ketone is present the solution will remain colourless.
-Tollens reagent is ammoniacal silver nitrate. It oxidises the aldehyde to a carboxylic acid and reduces silver ions to silver in the presence of an aldehyde. The silver can be seen deposited on the edge of the test tube (silver mirror)

78
Q

What are the reagents for the oxidation of an aldehyde to form a carboxylic acid?

A

-potassium dichromate - K2Cr2O7
-sulfuric acid- H2SO4

-reagents react in situ to form the oxidising species- Cr2O7 2- and H+

79
Q

What is the balanced ionic equation for the oxidation of ethanal to ethanoic acid?
What is the simplified balanced symbol equation?

A
80
Q

What is the general mechanism for the reduction of an aldehyde by nucleophiic addition ?

A

-sodium borohydride NaBH4 is a reducing agent the compound is made out of BH4- ion which acts as a source of hydride ions H-
-this is involved in nucleophilic addition reactions to form alcohols

81
Q

What is the reaction mechanism of the reaction of hydrogen cyanide with propanone?

A
82
Q

What is the balanced equation for the formation of a cyanide nucleophile from hydrogen cyanide?

A

HCN + H2O ⇌CN- + H3O+

Chemistry Alevel OCR (9 decks)

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