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Module 6 Chemistry > Chapter 26 - Carbonyl Compounds > Flashcards

Chapter 26 - Carbonyl Compounds Flashcards

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1
Q

what is the carbonyl functional group and what is it not

A

C = O

where the carbon is connected to other carbons or hydrogens NOT an oxygen or anything else

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2
Q

what is the difference between aldehydes and ketones and what is their general formula

A
  • aldehydes have the C=O bond at the end of a carbon chain
  • Ketones do not have it at the end
    CnH2nO
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3
Q

what occurs in the oxidation of a primary alcohol and what are the reactants and conditions

A

primary alcohol + [O] —> aldehyde + water

  • acidified potassium dichromate
  • distillation

OR

primary alcohol + 2[O] —> carboxylic acid + water

  • acidified potassium dichromate
  • reflux
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4
Q

what occurs in the oxidation of an aldehyde and what are the conditions

A

aldehyde + [O] —> carboxylic acid

  • reflux
  • potassium dichromate (acidified)
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5
Q

what occurs in the oxidation of a secondary alcohol and what are the conditions

A

secondary alcohol + [O] —> Ketone + water

  • reflux
  • acidified potassium dichromate
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6
Q

do ketones further oxidise

A

no

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7
Q

what is the colour change for all of these oxidations

A

orange —> green

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8
Q

what are the differences between the C=C double bond and the C=O bond

A
  • they have the same structure, a sigma bond and a pi bond
  • however C=O is polar because the oxygen is more electronegative, C=C is not
  • C=O attracts nucleophiles as the carbon is delta +ve
  • C=C has an electron dense region so attracts electrophiles
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9
Q

what do aldehydes and ketones reduce to and what is the reducing agent and conditions

A
  • aldehydes reduce to primary alcohols
  • Ketones reduce to secondary alcohols
  • the reducing agent is NaBH4(aq)
  • represented by [H]
  • solution is warmed
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10
Q

what is the mechanism for the reduction of aldehydes and ketones

A

1) NaBH4 splits to form a Hydride ion
2) the lone pair on the hydride ion attacks the delta+ve carbon forming a daitive covalent bond
3) the Pi bond of the C=O breaks by heterolytic fission forming a negatively charged intermediate
4) the intermediate is protonated (from H2O) to form an alcohol

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11
Q

what is the reaction of carbonyl compounds with HCN

A
  • HCN adds across the double bond =
  • H2SO4 and NaCN is used to provide the HCN as the reaction occurs
  • it increases the length of the carbon chain
  • forms effectively an alcohol with a cyanide group on
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12
Q

what is the mechanism for the reaction of carbonyls with HCN

A

1) HCN splits into H+ and CN-
2) the lone pair of electrons on the carbon attacks the delta+ve carbon
3) the rest happens as before but with H+ not H2O

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13
Q

what are the three ways to detect or distinguish between carbonyls

A
  • Brady’s
  • Tollens’
  • Acidified Dichromate
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14
Q

what is the brady’s reaction

A

1) add 5cm depth of 2,4 DNPH
2) add a few drops of the unknown substance
3) if no crystals form, add H2SO4
4) an orange precipitate indicates an aldehyde or ketone

  • if a carbonyl compound is present, an orange precipitate forms
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15
Q

what is the Tollens’ reagent reaction and how can we make Tollens

A

1) add approx. 3cm depth of AgNO3 (aq) to a test tube
2) add NaOH to form a brown precipitate
3) add dilute ammonia until the brown precipitate dissolves - this is tollens
4) add equal vols of tollens and unknown to a test tube
5) leave for 15mins at 50 degrees

if a silver mirror forms then its an aldehyde, otherwise it’s a ketone

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16
Q

what is the acidified dichromate experiment

A

1) add a few drops of H2SO4 and K2Cr2O7 to a test tube

2) if there is a colour change of orange —> green then its an aldehyde, otherwise its a ketone

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17
Q

what is the extension to the brady’s (2,4DNPH) reaction that can be used to identify the exact carbonyl compound

A

1) filter the precipitate
2) recrystallise the precipitate and leave to dry
3) find its melting point and compare to standard values

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18
Q

what is a carboxylic acid and what is the carboxyl group

A
  • a carboxylic acid is an organic acid which contains the carboxyl functional group
  • it contains a carbonyl group and a hydroxyl group COOH
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19
Q

what is the solubility of carboxylic acids

A
  • they dissolve well in water as the polar C=O and O-H groups can disrupt and form hydrogen bonds with the water molecules
  • solubility decreases with chain length
  • up to butanoic acid are soluble
20
Q

how do the melting and boiling points of carboxylic acids compare

A
  • higher boiling points than similar length or molecular sized alcohols
  • because they’re able to form more hydrogen bonds
21
Q

what are the 3 main reactions of carboxylic acids

A
  • with SOCl2 to form Acyl Chlorides
  • with itself to form acid anhydrides
  • with alcohols to form esters
22
Q

what sort of acids are carboxylic acids, give an equation

A
  • they are weak acids
    CH3COOH —> CH3COO- + H+
    REVERSIBLE REACTION
  • partially dissociate in water
23
Q

what is a derivative of a carboxylic acid

A

a derivative of a carboxylic acid is a compound that can be hydrolysed to form the parent carboxylic acid

24
Q

what is hydrolysis

A

“hydrolysis is the chemical breakdown of a compound in the presence of water or in aqueous solution”

25
Q

what are esters

A

they are compounds which contain the ester functional group of
RCOOR

26
Q

what is the main physical property of esters

A

they are more volatile than alcohols as they have no OH group so can’t form as many hydrogen bonds

27
Q

what is the equation for making esters from carboxylic acids (esterification)
what is the sort of reaction and what is the catalyst

A

carboxylic acid + alcohol —> ester + water
REVERSIBLE REACTION
Conc. H2SO4

28
Q

how can we make esters: esterification

A

1) add approx. 2cm^3 of both a carboxylic acid and an alcohol to a test tube
2) add a few drops of concentrated sulphuric acid (catalyst)
3) heat at 80 degrees for 5 mins
4) add sodium carbonate to react with any excess acid

29
Q

what are the two types of ester hydrolysis

A

acidic and alkaline

30
Q

what occurs in acidic ester hydrolysis, what is the use of the acid

A

ester + water —> carboxylic acid + alcohol

REVERSIBLE REACTION

  • effectively the reverse of esterification
  • heated under reflux, acid acts as a catalyst
  • reversible reaction
  • any dilute aqueous acid
31
Q

what occurs in alkaline ester hydrolysis

A
  • known as saponification
  • irreversible

Ester + OH- —> carboxylate ion + alcohol

32
Q

how can we form acyl chlorides from carboxylic acids

A

carboxylic acid + Thionyl chloride (SOCl2) —-> acyl chloride + sulphur dioxide(g) + Hydrogen Chloride(g)

33
Q

what are the 4 main reactions of acyl chlorides

A
  • with alcohols/phenols to form esters
  • with water to form carboxylic acids - hydrolysis
  • with 2NH3 to form primary amides
  • with CH3NH2 and other primary amines to form secondary amides
34
Q

how do acyl chlorides react with phenols and alcohols

A

Acyl Chloride + alcohol —> ester + HCl(g)

35
Q

how do acyl Chlorides react with water (hydrolysis) to form carboxylic acids

A
  • violent reaction
  • steamy HCl(g) fumes

Acyl Chloride + water —> Carboxylic acid + HCl(g)

36
Q

how do Acyl Chlorides react with ammonia

A

Acyl Chloride + 2NH3 —-> Primary amide + ammonium chloride

37
Q

how do acyl chlorides react with primary amines

A

acyl chloride + primary amine —-> secondary amide + acyl ammonium chloride

38
Q

how is an acid anhydride formed

A

carboxylic acid + carboxylic acid —> acid anhydride + water

39
Q

how does an acid anhydride react with alcohols (esterification)

A

acid anhydride + alcohol —-> ester + carboxylic acid

40
Q

which of the reactions of carboxylic acids and its derivatives are reversible and why might they have low yields

A

esterification/hydrolysis of esters
dissociation of a carboxylic acid

they are in equilibrium and therefore cannot have a 100% yield

41
Q

what is the organic product formed in the Tollens’ reagent reaction/redox systems

A

Aldehyde oxidises to a carboxylic acid, silver ions reduce to silver solid

carboxylic acid is organic product

42
Q

what is the name of the product of the hydrogen cyanide and carbonyl compound reaction

A

Hydroxynitrile

43
Q

how can hydroxynitriles react with water

A

they can be hydrolysed with only water or under acidic and alkaline conditions

44
Q

what occurs in acidic hydrolysis of hydroxynitriles, what are the reactants

A
  • heat under reflux with a dilute acid
    CH3CN + 2H2O + HCl —> CH3COOH + NH4+Cl-
  • instead of forming an ammonium salt as you do with just water, it (the ethanoate ions) reacts further with the H+ ions to form a carboxylic acid
45
Q

why are acyl chlorides more acidic than carboxylic acids in water

A
  • they will react with water to form HCl and a carboxylic acid, HCl is a strong acid
  • whereas carboxylic acids only slightly dissociate
46
Q

what makes a molecule able to form a silver mirror with Tollens’ reagent and therefore what is the only carboxylic acid which does

A

it must have a C-H bond as these are the only bonds with a low enough bond enthalpy for the molecule to be oxidised by Tollens’/ reduce Tollens’ to silver

Hence methanoic acid is the only carbox acid which can

Module 6 Chemistry (6 decks)

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