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OCR A a-level chemistry > Module 6 - [ch26] (carbonyls and carboxylic acids) > Flashcards

Module 6 - [ch26] (carbonyls and carboxylic acids) Flashcards

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1
Q

What is the functional group of aldehydes and ketones and what distinguishes one from another?

A

carbonyl functional group
C=O

the position of the C=O differs

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2
Q

Where are the functional group of carbonyls, aldehydes and ketones found?

A

aldehydes - the carbonyl functional group is found at the end of a carbon chain

ketone - the functional group is joined to two carbon atoms in the carbon chain

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3
Q

what are aldehydes oxidised to?

A

carboxylic acids

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4
Q

conditions for oxidation of an aldehyde

A

refluxed with acidified potassium dichromate

dichromate solution turns from orange to green

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5
Q

What is the difference in the way carbonyls react and alkenes react

A

alkenes - C=C non-polar bond
carbonyls - C=O polar bond

carbonyls react with some nucleophiles by nucleophilic addition

alkenes react with electrophiles by electrophilic addition

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6
Q

Why is the C=O bond polar

A

Oxygen is more electronegative than carbon
the electron density lies closer to the oxygen atom making the oxygen end slightly negative and the carbon end delta positive

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7
Q

What is NaBH4 used as reacting with carbonyl compounds

A

reducing agent

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8
Q

what are aldehydes and ketones reduced to

A

aldehydes - primary alcohols
ketones - secondary alcohols

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9
Q

conditions for the reduction of carbonyl compounds

A

NaBH4
gently warmed with reducing agent in aqueous solution

+ 2[H] (reducing agent e.g)

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10
Q

what type of reaction is that of carbonyl compounds with HCN

A

addition reaction

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11
Q

describe hydrogen cyanide

A

colourless, extremely poisonous liquid

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12
Q

advantages of reaction of carbonyls with HCN

A

increases the chain length

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13
Q

aldehyde + HCN –H2SO4/H2O–>

A

hydroxynitrile

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14
Q

what type of reaction is the one by which aldehydes and ketones react to form alcohols

A

nucleophilic addition

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15
Q

describe mechanism for reaction of a carbonyl with NaBH4

A

lone pair on hydride ion (from NaBH4) attracted to delta plus charge on carbon atom
dative covalent bond formed between hydride ion and carbon atom
Pi bond breaks apart by heterolytic fission making oxygen negative (intermediate)
Lone pair on oxygen donated to a delta positive hydrogen in a water molecule
= alcohol + OH-

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16
Q

describe mechanism for reaction of a carbonyl with HCN

A

lone pair of electrons on cyanide ion attacks electron deficient carbon atom
dative covalent bond formed
Pi bond breaks by heterolytic fission
Oxygen donates lone pair to hydrogen ion
hydroxynitrile formed

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17
Q

where is the negative charge on a CN

A

on the carbon atom

-:CN

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18
Q

What is used to detect the presence the presence of the carbonyl functional group?

A

brady’s reagent
2,4 DNP
2,4 dinitrophenylhydrazine

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19
Q

what is the positive test for the carbonyl functional group

A

2,4 DNP
yellow/orange precipitate forms

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20
Q

What is the issue with using 2,4 DNP to identify organic compounds

how is this overcome

A

gives a positive result for both aldehydes and ketones
further tests need to be carried out to distinguish between the two

taking melting point of precipitate, compare to database, distinguishes aldehydes from ketones

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21
Q

What is Tollen’s reagent? What is one of it’s properties?

A

a solution of silver nitrate in aqueous ammonia
silver complex ions in colourless solution

has a short shelf-life so must be made up immediately before carrying out a test

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22
Q

How do you test for an aldehyde

A

tollen’s reagent
gently warm (water bath 50 degrees)
produces a silver mirror

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23
Q

How do you prepare tollen’s reagent

A

Add silver nitrate in a test tube AgNO3(Aq)
Add aqueous sodium hydroxide NaOH until a brown precipitate of silver oxide Ag2O formed
Add dilute ammonia solution until precipitate dissolves to form clear and colourless solution

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24
Q

what is an carboxylic acid

A

an organic acid with the carboxyl functional group

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25
Q

Which carboxylic acids are soluble in water

A

carboxylic acids with up to 4 carbon atoms

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26
Q

Why are carboxylic acids soluble in water

A

C=O
O-H
polar bonds which can form hydrogen bonds with water molecules

27
Q

How does solubility of carboxylic acids change as chain length increases

A

solubility decreases
as chain length gets longer, the non-polar carbon chain has a greater effect on the overall polarity of the molecule than the carboxyl group

28
Q

what are dicarboxylic acids

A

have two polar carboxyl groups
solids at room temp and dissolve readily in water

29
Q

what type of acid are carboxylic acids

A

weak acids
partially dissociates

HCOOH <-> H+ HCOO-

30
Q

carboxylic acid + metal
PRODUCTS

A

carboxylate salt + hydrogen gas

31
Q

give a general formula for
carboxylic acid + metal

A

acid(COOH) + metal -> (negative acid ion)(metal positive ion) + H2(g)

32
Q

what type of reaction is that of a carboxylic acid and a metal

A

redox

33
Q

carboxylic acid + metal oxide

A

carboxylate salt + water

both Hs from H2O from the acid

34
Q

carboxylic acid + alkalis

A

carboxylate salt + water

one H from H2O from the acid, the other from the alkali

35
Q

carboxylic acid + carbonate

A

carboxylate salt + water + carbon dioxide

36
Q

how do you test for the carboxyl group

A

reaction with carbonate

37
Q

What is a derivative of a carboxylic acid

A

contain the acyl group

      O
    // R - C
     \
38
Q

what are four carboxylic acid derivatives

A

esters
acyl chlorides
acid anhydrides
amide

39
Q

naming acyl chlorides

e.g propanoic acid

A

-oyl chloride

propyl chloride

40
Q

how is an acid anhydride formed

A

removal of water from two carboxylic acid molecules

41
Q

what is esterification

A

reaction of alcohol with a carboxylic acid to form an ester

alcohol warmed with a carboxylic acid with a small amount of concentrated sulfuric acid (catalyst)

42
Q

alcohol + carboxylic acid

A

ester + water

43
Q

what is hydrolysis

A

chemical breakdown of a compound in the presence of water (or in aqueous solution)

44
Q

what is acid hydrolysis

A

ester heated under reflux with dilute aqueous acid
ester broken down by water with acid acting as a catalyst
reversible

45
Q

ester + water ->

A

carboxylic acid + alcohol

46
Q

alkaline hydrolysis

A

ester is heated under reflux with aqueous hydroxide ions
irreversible

47
Q

ester + hydroxide ions ->

A

carboxylate ion + alcohol

48
Q

how do you prepare an acyl chloride?

A

carboxylic acid + thionyl chloride

49
Q

thionyl chloride

A

SOCl2

50
Q

carboxylic acid + thionyl chloride ->

What are the safety precautions regarding this reaction?

A

acyl chloride + sulphur dioxide(g) + hydrochloric acid(g)

SO2(g) an HCl(g) harmful gases
reaction should be carried out in a fume cupboard

51
Q

why are acyl chlorides useful?

A

they are very reactive

can be converted into carboxylic acids derivates with good yields

52
Q

acyl chloride + alcohol ->

A

ester + HCl

53
Q

acyl chloride + phenol ->

A

ester + HCl

phenol
____
___/ O \
HO \ ____/

54
Q

acyl chloride + water ->

A

carboxylic acids + HCl fumes

55
Q

acyl chloride + ammonia ->

A

primary amide + ammonium chloride

COCl + 2NH3 -> CONH2 + NH4Cl

56
Q

acyl chloride + primary amine ->

A

secondary amide + HCl

57
Q

acid anhydrides

A

less reactive than acyl chlorides
but react in the same way

58
Q

what type of intermolecular forces do molecules with the carbonyl group have

A

permanent dipole-dipole due to the polar C=O

59
Q

which bond in carbonyl compounds is usually responsible for its reactions and why

A

C=O
the polarity of the bond
(difference in electronegativity between C and O)

60
Q

what is fehling’s solution and how is it used

A

copper complex ions
blue
test for an aldehyde, blue -> brick red
reduction to Cu+2 ions

61
Q

why does a silver mirror form when an aldehyde is added to tollen’s reagent

A

Ag+ ions are reduced to Ag(s)

62
Q

what is a reducing agent for aldehydes and ketone and what ions does it release in solution

A

NaBH4
H- ions

63
Q

how do you create a carboxylic acid from an aldehyde

A

oxidation
acidified potassium dichromate (K2Cr2O7/H2SO4)

OCR A a-level chemistry (11 decks)

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