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Georges chem > carbonyls and carboxylic acids chp 26 > Flashcards

carbonyls and carboxylic acids chp 26 Flashcards

1
Q

what is a carbonyl group

A

C=O

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2
Q

what structural similarities do aldehydes and ketones share

A

They both have a carbonyl group (C=O)

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3
Q

Where is the carbonyl group found in aldehydes

A
  • Is found at the end of the carbon chain
  • the carbon (C=O) is attached to 1 or 2 hydrogens
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4
Q

Where is the carbonyl functional group found in ketones

A
  • The carbonyl group is joined to 2 carbon atoms in the carbon chain
  • The ketone group is written as CO
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5
Q

How would you name aldehydes and ketones

A

You add the suffix -al for aldehydes and -one for ketones after the name of the longest carbon chain.

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6
Q

what is the product of oxidising aldehydes
draw reaction

A
  • They can be oxidised into carboxylic acids when refluxed with acidified dichromate (Na2Cr2O7 / K2Cr2O7 with dilute H2SO4)
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7
Q

What oxidation reactions do ketones undergo

A

They undergo none

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8
Q

What reaction mechanism can carbonyl comnpounds undergo

A
  • Nucleophilic addition reactions
  • This is due to the polarity of the C=O group, which attracts nucleophiles
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9
Q

what influences the reactivity of aldehydes and ketones

A

The C=O bond, made up of both a sigma-bond and a pi-bond

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10
Q

Why do carbonyl groups and alkenes react differently if they both contain a double bond

A
  • The C=C bond in alkenes is non-polar
  • The C=O bond in a carbonyl compound is polar
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11
Q

What makes a C=O bond polar

A
  • Oxygen is more electronegative than carbon
  • The electron density in the double bond lies closer to the oxygen atom that to the carbon.
  • ^This makes the carbon end slightly more positive and the oxygen end slightly more negative
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12
Q

What reaction mechanism does the C=C bonds in an alkene undergo

A

Electrophilic addition (NOT NUCLEOPHILIC ADDITION)

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13
Q

What is a nucleophile

A

A compound/molecule that donates electron pairs to areas of low electron density

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14
Q

What reducing agent is used when reducing ketones and aldehydes

A
  • Sodium tetrahydridoborate (III)
  • NaBH4
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15
Q

What conditions are used for the reduction of aldehydes and ketones

A
  • warm
  • reducing agent (NaBH4)
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16
Q

What is the product of reducing a aldehyde

A
  • They are reduced into primary alcohols
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17
Q

What is the product of the reduction of ketones

A
  • They are reduced into secondary alcohols
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18
Q

How can you write a reducing group in a reaction equation

A

2[H]

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19
Q

How does HCN (cyanide) react with carbonyl compounds

A

It adds across the C=O bond of aldehydes and ketones

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20
Q

What can be used to provide the hydrogen cyanide in a reaction due to hydrogen cyanide being dangerous

A

Sodium cyanide and sulphuric acid are used to provide the hydrogen cyanide in the reaction

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21
Q

why is the reaction of hydrogen cyanide so important for organic chemistry

A
  • The reaction is very useful as it provides a way to increase the length of the carbon chain
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22
Q

Why is hydrogen cyanide dangerous to use in the lab

A
  • It is a colourless, extremely poisonous liquid that boils slightly above room temperature
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23
Q

What type of reaction is the reaction of carbonyl groups with hydrogen cyanide

A
  • its an addition reaction
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24
Q

What functional groups does the organic product formed from the reaction of an aldehyde with hydrogen cyanide contain

A
  • It contains a hydroxyl group -OH, and a nitrile C≡N
  • These compound are classed as hydroxynitriles (or cyanohydrins)
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25
Q

Draw the reaction mechanism for the nucleophilic addition of NaBH4 with a carbonyl compound

A
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26
Q

Explain the mechanism for the nucleophilic addition of NaBH4 with a carbonyl compound

A
  • Hydride ion has lone pair
  • Dative covalent bond forms between hydride ion and carbon in C=O
  • C=O (pi-bond) breaks by heterolytic fission
  • negative intermediate formed
  • oxygen atom from carbonyl group donates lone pair to hydrogen in water molecule
  • Intermediate has been protonated to form an alcohol
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27
Q

Draw the reaction mechanism for the reaction of a carbonyl group and cyanide

A
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28
Q

Explain the reaction mechanism for the reaction of carbonyl compunds with cyanide

A
  • electron pair from :CN- attracts and donated to δ+ carbon in carbonyl group
    ^dative covalent bond forms
  • pi-bond in C=O bond breaks by heterolytic fission,
    ^forms negatively charged intermediate
  • intermediate protonated by donating lone pair to a hydrogen ion,
  • The product is a hydroxynitrile
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29
Q

what is used to detected the presence of the carbonyl functional group in aldehydes and ketones, what does a positive and negative result look like

A
  • Bradys reagents (2,4-dinitrophenylhydrazine)
  • In the presence of a carbonyl group a yellow/orange precipitate is produced
  • the reaction between bradys reagent and aldehydes and ketones is a condensation reaction
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30
Q

How is Bradys reagent used in the lab to test for carbonyl groups

A
  • 2,4-DNP dissolved in methanol and sulfuric acid as a pale orange solution (this is then called Bradys reagent)
31
Q

what is the method for testing for carbonyl groups in aldehydes and ketones

A

1)Add 5cm depth of a solution of 2,4 - DNP to a clean test tube. This is in excess
2)Using a dropping pipette, add 3 drops of the unknown compound. leave to stand
3)If no crystals form, add a few drops of sulfuric acid
4)A yellow/orange precipitate indicates the presence of an aldehyde or ketone

32
Q

what can be used to distinguish between aldehydes and ketones

Draw what is oxidised and reduced during a positive result

A
  • tollens’ reagent (a solution of silver nitrate in aqueous ammonia)
  • in the presence of an aldehyde group, a silver mirror is produced
33
Q

what is the method for producing tollens reagent

A
  • add 3cm depth of (aq) silver nitrate, AgNO3 to a test tube
  • Add (aq) sodium hydroxide, NaOH, to silver nitrate until brown precipitate of silver oxide forms
  • Add dilute ammonia solution until brown precipitate just dissolves to form a clear colourless solution
34
Q

What is the method for carrying out the test for aldehydes

A

1)Pour 2cm depth of the unknown solution into a test tube
2)Add an equal volume of the freshly prepared pollens reagent
3)Leave the test tube to stand in a beaker of warm water at 50°C for about 10-15 mins and then observe weather any silver mirror is formed

35
Q

what is reduced and oxidised in the reaction between an aldehyde and tollens reagent

A
  • silver ions are reduced to silver
  • aldehyde is oxidised to a carboxylic acid
36
Q

what is the method for using melting point to identify the carbonyl compound

A

1) The impure solid is filtered to separate the solid precipitate from the solution
2)The solid then recrystallised to produce a pure sample of crystals
3)The melting point of the purified 2,4-DNP is measured and compared to a database of known melting points

37
Q

What pre-existing groups does a carboxyl group contain

A
  • carbonyl group
  • hydroxyl group
38
Q

what are the main organic reactions that carboxylic acid is involved in

A
  • Ester Formation: Carboxylic acids + alcohols → esters
  • Acyl Chloride Formation: Carboxylic acids + SOCl2 → acyl chlorides
  • Amide Formation: Carboxylic acids + amines → amides
  • Decarboxylation: Carboxylic acids → alkanes (conc H2SO4 or nickel and high temps)
  • acid anhydride formation: 2 carboxylic acid -condensation-> acid anhydride
39
Q

what suffix is used to name a carboxylic acid

A
  • oic acid is added to the stem of the longest carbon chain
40
Q

are carboxylic acids soluble

A
  • The C=O and O-H in carboxylic acids are both polar and so can form hydrogen bonds
  • carboxylic acids with up to 4 carbon atoms are soluble
  • As carbon chain increases the solubility decreases as more and more of the molecule is non-polar
41
Q

What are dicarboxylic acids and are they soluble

A
  • these are molecules with 2 carboxyl groups
  • they solid at room temp but dissolve readily in water
42
Q

are carboxylic acids weak or strong acids

A
  • they are classified as weak acids
  • when dissolved they only partially dissociate
43
Q

what reagents are used in neutralisation and redox reactions involving carboxylic acids, what products are always formed

A
  • redox reactions with metals
  • Neutralisation reactions with bases (alkalis, metal oxides, carbonates)
  • carboxylate salts are formed
44
Q

what is the suffix used in the nomenclature of the carboxylate ion in a carboxylate salt

A

changes from -oic acid to -ate

45
Q

what is produced in the reaction between carboxylic acids and metal

A
  • its a redox reaction
  • Hydrogen gas and carboxylate salt is formed
46
Q

What is produced from a carboxylic acid + metal oxide reaction

A

salt + water

47
Q

carboxylic acid + alkalis = ?

A

salt + water

47
Q

what can be used to distunguish between phenols and carboxylic acids

A
  • A carbonate can be used
  • carboxylic acid + carbonate would show CO2 is given off as effervesence
  • phenols are not acidic enough to react with carbonates
47
Q

carboxylic acids + carbonates =?

A

salt + carbon dioxide + water

48
Q

what is meant by a derivative of a carboxylic acid

A
  • a compound than can be hydrolysed to form the parent carboxylic acid
49
Q

draw an acyl group

A
50
Q

what are examples of carboxylic acid derivatives

A

esters, acyl chlorides, acid anhydrides and amides

51
Q

How do you name esters

A
  • remove the -oic acid suffix from the parent carboxylic acid and replace with -oate.
  • The alkyl chain attached to the oxygen atom of the COO group is then added as the first word in the name
52
Q

How do you name acyl halides

A
  • remove the oic acid and replace with -noyl halides
53
Q

How are acid anhydrides formed

A
  • formed by the removal of water from 2 carboxylic acids molecules
54
Q
  • what reaction brings about esterification
  • what conditions are needed
A
  • The reaction of an alcohol with a carboxylic acid to form an ester.
  • alcohol is warmed
  • small amount of concentrated H2SO4 needed
55
Q

what can esters be hydrolysed by

A
  • aqueous acid or alkali
56
Q

what is acid hydrolysis in reference to esterification

A
  • it is the opposite of esterification
57
Q
  • what are the products of an acid hydrolysis of an ester
  • what are the conditions to carry out the reaction
A
  • ester is heated under reflux with dilute aqueous acid
  • ester broken down by water, with the acid acting as a catalyst
  • products are a carboxylic acid and an alcohol
    ^alcohol is the group from bonded to the oxygen of the ester
58
Q

what is alkaline hydrolysis also known as

A

saponification

59
Q

characteristics of alkaline hydrolysis of esters

A
  • it is irreversible
  • the ester is heated under reflux with aqueous hydroxide ions
  • products are an ester ion and an alcohol (that was alkyl group attached to oxygen)
60
Q

How can acyl halides be prepared

A
  • reacting the parent carboxylic acid with thionyl halide, SOX2
  • the other products are SO2 and HX (evolved as gases)
  • reaction should be done in fume cupboard
61
Q

How are acyl chlorides useful in organic synthesis

A
  • they are very reactive
  • can be easily converted into carboxylic acid derivatives with good yield
  • they react with nucleophiles by losing the chloride ion but retaining the C=O
62
Q

acyl halide + alcohol = ?

A
  • esters + H-halide
63
Q

acyl chlorides/acid anhydrides + phenols = ?

A
  • phenyl esters + HCl

neither reaction needs an acid catalyst

64
Q

acyl chloride + water = ?

A
  • carboxylic acid + HCl
  • violent reaction, evolutions of dense steamy HCl fumes
65
Q

During a reaction between acyl chloride and ammonia/amine what does the ammonia/amine act as

A

Acts as nucleophiles by donating a lone pair of electrons on the nitrogen atom to an electron-deficient species

66
Q

acyl chloride + ammonia =

A
  • primary amides + ammonium chloride
67
Q

what is meant by a primary amide

A
  • the nitrogen in the amide group is only attached to one carbon atom
68
Q

primary amine + acyl chloride = ?

A
  • secondary amine
69
Q

what is meant by a secondary amine

A
  • The nitrogen atom is attached to 2 carbon atoms
70
Q

How do acid anhydrides react with phenols, water, ammonia and amines

A
  • they react similarly to acyl chlorides
  • they are less reactive than acyl chlorides
71
Q

draw the reaction mechanism of the reaction between acyl chlorides and nucleophiles

A

Georges chem (29 decks)

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