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A-Level OCR Chemistry > Module 6: Chapter 26 (Carbonyls & Carboxylic Acids) > Flashcards

Module 6: Chapter 26 (Carbonyls & Carboxylic Acids) Flashcards

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1
Q

Describe the oxidation reaction of a primary alcohol?

A

Distillation
H+/Cr2O7^2- (acidified dichromate)
primary alcohol + [O] -> aldehyde + water
orange to green

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2
Q

Describe the oxidation reaction of a secondary alcohol?

A

Reflux
H+/Cr2O7^2- (acidified dichromate)
secondary alcohol + [O] -> ketone + water
orange to green

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3
Q

Describe the oxidation reaction of a tertiary alcohol?

A

Reflux
H+/Cr2O7^2- (acidified dichromate)
NO REACTION TAKES PLACE
solution remains orange

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4
Q

Describe the colour change of acidified dichromate?

A

H+/Cr2O7^2- ORANGE -> [Cr(H2O)5SO4]+ “Cr3+” GREEN

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5
Q

What functional group do aldehydes and ketones both contain and where is it found on the carbon chain?

A

Both contain the carbonyl functional group C=O

  • Aldehydes: C=O found at the end of the carbon chain
  • Ketones: C=O is joined to 2 different carbon atoms in the chain
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6
Q

How do you name aldehydes?

A

Adding “-al” as a suffix

PentanAL, ethanAL etc

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7
Q

How do you name ketones?

A

Adding “-one” as a suffix

Propanone, pentan-2-one, hexan-2-one etc

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8
Q

What happens when aldehydes are further oxidised?

A
  • Aldehydes can be further oxidised to carboxylic acid

Aldehyde + [O] -(reflux H+/Cr2O7^2-)-> carboxylic acid

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9
Q

How can scientists distinguish between ketones and aldehydes?

A

Further oxidation as ketones can’t be further oxidised, meanwhile aldehydes will become carboxylic acids

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10
Q

What are aldehydes reduced into?

A

Primary alcohols
- warmed with aqueous tetrahydridoborate (III) NaBH4 (the reducing agent)
aldehydes + 2[H] -NaBH4-> primary alcohols

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11
Q

What are ketones reduced into?

A

ketones + 2[H] -NaBH4-> secondary alcohols

- warmed with aqueous tetrahydridoborate (III) NaBH4 (the reducing agent)

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12
Q

Describe the C=O bond

A

C=O bond is composed of a σ-bond and a π-bond

  • the σ-bond is caused by direct overlap of orbitals between the C and O
  • the π-bond is formed by sideway overlap of p-orbitals above and below the place of C and O atoms
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13
Q

Why is the C=O polar?

A
  • Oxygen is more electronegative than carbon
  • Electron density in the double bond lies closer to the oxygen atom than to the carbon atom
  • This makes the carbon end partially positive and the oxygen end partially negative
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14
Q

What happens because of the polar C=O bond?

A

Due to partially positive bond on carbon, carbonyl compounds will react with nucleophiles in a nucleophilic addition reactions

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15
Q

What is a nucleophile?

A

An electron pair donor

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16
Q

Draw the mechanism of carbonyl compounds with HCN

A

Check in book

:CN- reacts first with carbon
H+ from HCN reacts with O

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17
Q

Describe the reaction of carbonyl compounds with HCN

A
  • HCN adds across C=O bond
  • HCN is extremely poisonous so NaCN/H2SO4 is used to provide HCN
  • reaction increases carbon chain length
  • organic product is a hydroxynitrile
  • nucleophilic addition reaction
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18
Q

Draw the mechanism of an aldehyde being reduced

A

check in book

H- ion has 2 electrons that are from different atoms and comes from NaBH4
H from H2O makes hydroxyl group with oxygen

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19
Q

Draw the mechanism of a ketone being reduced

A

check in book

H- ion has 2 electrons that are from different atoms and comes from NaBH4
H from H2O makes hydroxyl group with oxygen

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20
Q

What type of reaction is ketone/aldehyde and HCN (H+/NaCN)?

A

Nucleophilic addition

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21
Q

What reagent can be used to detect presence of a carbonyl group in a ketone or aldehyde?

A

Brady’s reagent (yellow/orange precipitate)

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22
Q

What is Brady’s reagent?

A
  • Solution of 2,4-DNP dissolved in methanol and sulfuric acid
  • Detects presence of a carbonyl functional group in ketones or aldehydes only
  • Positive test results in a yellow/orange precipitate forming
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23
Q

How can the identity of ketones and aldehydes be determined?

A
  1. Separate precipitate by filtration from solution
  2. Recrystallise to obtain a pure sample
  3. Measure the melting point
  4. Measured melting point can be compared to known values
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24
Q

What reagent can be used to distinguish between aldehydes and ketones?

A

Tollen’s reagent

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25
Q

What is Tollen’s reagent?

A

Solution of silver nitrate in aqueous solution

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26
Q

What is the positive test result of using Tollen’s reagent?

A

In the presence of an aldehyde only a silver mirror is formed in an oxidation reaction

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27
Q

What reactions happen with Tollen’s reagent with a positive test result?

A

Ag+ ions act as the oxidising agent, Ag+ ions are reduced to silver and aldehyde is oxidised to a carboxylic acid

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28
Q

What is the functional group of carboxylic acids?

A

-COOH (or -CO2H)

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29
Q

What are the partial charges on the carboxyl functional group?

A

partially positive = C and H

partially negative = O

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30
Q

How are carboxylic acids synthesised?

A

Oxidation of primary alcohols (heating with H+/K2Cr2O7 under reflux)

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31
Q

What is the suffix (naming) or carboxylic acids?

A

-oic acid (Methanoic Acid)

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32
Q

What is a dicarboxylic acid?

A
  • Contains 2 carboxyl functional groups

- suffix “-dioic acid” final e is kept of the alkane (e.g. Ethanedioic acid)

33
Q

How are benzene rings named with carboxylic acids?

A

Benzoic acid

34
Q

What type of acids are carboxylic acids?

A

Weak acids, they only partially dissociate in aqueous solution
CH3COOH(aq) ⇌ H+(aq) + CH3COO-(aq)

35
Q

Describe the solubility of carboxylic acids?

A

The presence of polar C=O and O-H bonds means that carboxylic acids can form hydrogen bonds to themselves and also with water molecules
- hydrogen bonds can form at 3 places on the carboxyl function group with water

36
Q

Describe the trend in solubility within carboxylic acids?

A

As the number of carbon atoms increases, the non-polar carbon chain has a greater effect on the overall polarity of the molecule, and the solubility decreases.

37
Q

Describe the trend in boiling points with carboxylic acids?

A

as the length of the carbon chain increases melting points increase as more hydrogen bonds have to break between molecules

38
Q

Describe the reaction between carboxylic acids and alkalis?

A

Alkali + Carboxylic Acid -> Carboxylate + Water

  • Neutralisation reaction
  • e.g. KOH (aq) + CH3COOH (aq) → CH3COOK (aq) + H2O(l)
  • can omit charges on carboxylate ion CH3COO-K+(aq)
  • potassium ethanoATE produced (sodium salt of ethanoic acid)
39
Q

What is the ionic equation for the reaction between carboxylic acid and an alkali?

A

H+(aq) + OH- (aq) → H2O (l)

40
Q

What is the reaction between carboxylic acid and a carbonate?

A

Carboxylic acid + Carbonate → Carboxylate + CO2 + H2O

  • e.g. Na2CO3(aq) + 2CH3COOH (aq) → 2 CH3COONa(aq) + CO2(g) + H2O(l)
  • sodium ethanoate produced
  • neutralisation (?)
41
Q

What is the reaction between carboxylic acid and a metal?

A

Carboxylic Acid + Metal → Carboxylate + Hydrogen Gas

  • E.g. Mg(s) + 2CH3COOH(aq) → (CH3COO)2Mg(aq) + H2(g)
  • Magnesium Ethanoate produced (CH3COO-)2Mg^2+
  • redox reaction (?)
42
Q

How do you draw a salt produced from a carboxylic acid?

A

drawing the molecules in full, you draw the negative charge on the O molecule and the metal molecule next to it with the positive charge, e.g. O-Na+
- if the metal has a charge greater than +1 then the organic molecule doubles and write brackets around it

43
Q

What are the 7 reactions involving carboxylic acids?

A

carboxylic acid + metal -> salt + hydrogen
carboxylic acid + metal oxide -> salt + water
carboxylic acid + alkali -> salt + water
carboxylic acid + carbonate -> salt + water + CO2

carboxylic acid + alcohol -> ester + water
carboxylic acid + SOCl2 -> acyl chloride + SO2 + HCl
carboxylic acid + carboxylic acid -> acid anhydride + H2O

44
Q

What is a derivative of a carboxylic acid?

A

compound that can be hydrolysed to form the parent carboxylic acid

45
Q

What are the 4 derivatives of carboxylic acids?

A

ester
acyl chloride
amide
acid anhydride

all have the acyl RCO group

46
Q

How do you name an ester?

A
  • first part of the name is the alkyl group from the alcohol ( e.g. propanol becomes propyl)
  • second part of the name is from the carboxylic acid, “oic acid” replaced by “oate” (e.g. ethanoic acid becomes ethanoate

Propyl Ethanoate

47
Q

What is the general reaction for an ester?

A

carboxylic acid + alcohol ⇌ ester + water

48
Q

What conditions does esterification happen under?

A
  • catalysed by concentrated sulfuric acid (acidic)
  • under reflux
  • condensation reaction
  • reversible reaction eventually becomes an epm
49
Q

Methanol + butanoic acid?

A

Methanol + butanoic acid ⇌ methyl butanoate + water

with concentrated H2SO4 under reflux

50
Q

What bond is broken in ester hydrolysis?

A

single C-O bond

51
Q

What is hydrolysis?

A

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

52
Q

What is a condensation reaction?

A

2 small molecules react together to form a larger molecule, with the elimination of a small molecule such as water

53
Q

What happens in acid hydrolysis?

A

ester + water ⇌ carboxylic acid + alcohol

  • heated under reflux
  • catalysed with dilute aqueous acid
  • excess water can be added to push epm to the right and increase yield
54
Q

What happens in alkaline hydrolysis?

A

ester + water -> salt + alcohol

  • salt is a sodium carboxylate (write the charges in structure)
  • irreversible
  • heated under reflux with NaOH(aq) solution
55
Q

What is the structure of an acyl chloride?

A

Cl attached to a C attached to = O

56
Q

How are acyl chlorides formed?

A

carboxylic acid + thionyl chloride (SOCl2) -> acyl chloride + sulfur dioxide (SO2(g)) + hydrogen chloride (HCl(g))
- harmful gases produced

57
Q

How do you name an acyl chloride?

A

replace -oic acid with -oyl chloride

58
Q

Are acyl chlorides reactive?

A
  • very reactive
  • very useful in organic synthesis
  • react with nucleophiles by losing Cl- whilst retaining C=O
59
Q

Draw/write the structure of an acid anhydride?

A

ethanoic anhydride

H3C-C(=O)-O-C(=O)-CH3

60
Q

How is an acid anhydride made?

A

removing water from 2 carboxylic acid molecules

2 carboxylic acid -> acid anhydride + water

61
Q

How do you name an acid anhydride?

A

replace acid with anhydride

62
Q

What are the 3 reactions for preparing esters?

A
  1. carboxylic acid + alcohol ⇌ ester + water (with concentrated acid catalyst)
  2. acyl chloride + alcohol -> ester + hydrogen chloride
  3. acid anhydride + alcohol -> ester + carboxylic acid
    - no catalyst needed as they are more reactive than carboxylic acids
63
Q

Ethanol + propanoyl chloride

A

Ethanol + propanoyl chloride -> ethyl propanoate + HCl

64
Q

Ethanol + ethanoic anhydride

A

Ethanol + ethanoic anhydride -> ethyl ethanoate + ethanoic acid

65
Q

What is a phenol?

A

the hydroxyl group is attached directed to a benzene ring (hexagon)

66
Q

What are the 2 reactions for phenols?

A

acyl chloride + phenol -(room temp)-> ester + hydrogen chloride
acid anhydride + phenol -(heat under reflux)-> ester + carboxylic acid
- acylating agents
- anhydrous conditions

67
Q

What are the 4 overall reactions of acyl chlorides?

A

acyl chloride + alcohol -> ester + HCl
acyl chloride + phenol -> ester + HCl
acyl chloride + water -> carboxylic acid + HCl
acyl chloride + ammonia -> amide + ammonium chloride

68
Q

What are the 5 overall reactions of carboxylic acids?

A

carboxylic acid + metal -> salt + hydrogen
carboxylic acid + alkali -> salt + water
carboxylic acid + metal oxide -> salt + water
carboxylic acid + carbonate -> salt + water + CO2
carboxylic acid + alcohol -> ester + water

69
Q

What are the 2 reactions for acid anhydrides?

A

acid anhydride + alcohol -> ester + carboxylic acid

acid anhydride + phenol -> ester + carboxylic acid

70
Q

Ethanoic acid + Ca

A

(H3CCOO-)2Ca^2+ (write this even in formula) + H2

71
Q

Propanoic acid + MgO

A

(CH3CH2COO-)2Mg2+ + H2O

72
Q

Ethanoic acid + KOH

A

CH3COO-K+ + H2O

73
Q

Propyl butanoate + water

A

Propyl butanoate + water ⇌(dilute acid) propanol + butanoic acid

74
Q

How can you distinguish between ketones and aldehydes? (ie after Brady’s reagent has been added)

A
  • recrystallise to purify
  • find the melting points
  • compare it with known values
75
Q

Bond angles in the COOH

A

angle around C = 120º

angles around O = 104.5º

76
Q

What happens if you add HCl to a compound with more than one ester groups?

A

C-O bond splits in all ester groups and creates more products

77
Q

What happens if a molecule has a hydroxyl group at one end and a carboxyl group at another, then in refluxed with an acid catalyst?

A

functional groups react with each other on the same molecule (form a ring)

78
Q

What are the apparatus parts of reflux?

A
  • condenser (water out on top and water in on bottom)
  • pear shaped flash
  • anti bumping granules
79
Q

What is the process of reflux?

A

A technique used for boiling volatile/flammable reactants/products over a prolonged period of time.
- any vapour formed is condensed back to a liquid and returned to the pear-shaped flask

A-Level OCR Chemistry (21 decks)

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