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Alevel Chemistry Edexcel > Topic 17 - Organic Chemistry 2 > Flashcards

Topic 17 - Organic Chemistry 2 Flashcards

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1
Q

What are optical isomers?

A

stereoisomers where two molecules have the same molecular formula but different spatial arrangements due to a chiral centre, causing them to be non-superimposable on their mirror image
-rotate the plane of polarised light in opposite centres

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2
Q

What is a chiral centre?

A

an atom surrounded by 4 different atoms/groups

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3
Q

How do properties differ between enantiomers?

A
  • have same physical and chemical properties (eg. mp/bp, viscosity, way they react, etc)
  • have different biochemical properties (eg. interactions with enzymes and active sites)
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4
Q

How can enantiomers be separated?

A

by thin layer chromatography (TLC)

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5
Q

What is a racemic mixture?

A

a solution containing equal quantities of the two enantiomers
-is optically inactive (as the enantiomers cancel eachother out)

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6
Q

What is a polarimeter?

A

an instrument which measures the rotations of monochromatic light to identify +/- enantiomers

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7
Q

Does an SN1 reaction produce optically active or optically inactive products? And why?

A

optically inactive products

  • 2 enantiomers are produced (a racemic mixture)
  • because nucleophile can attack from above or below the plane
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8
Q

Does an SN2 reaction produce optically active or optically inactive products? And why?

A

optically active products

  • only 1 enantiomers are produced
  • because nucleophile can only attack from the opposite side to the leaving group
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9
Q

How do the smells of aldehydes and ketones differ?

A

aldehydes - bitter/sour smell

ketones - sweet smell

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10
Q

Are carbonyl compounds soluble in water?

A

yes -can H-bond with water
-solubility decreases down homologous series as alky chains interfere with H-bonds so an increased chain length so London forces become stronger than H-bonds

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11
Q

What are the melting and boiling points of carbonyl compounds like in comparison to alkanes and alcohols?

A

higher than alkanes
lower than alcohols
-PD interactions

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12
Q

What is the test for carbonyl bonds?

A

Brady’s reagent aka 2,4DNP (2,4 dinitrophenyl hydrazine)

+ve result = orange ppt (aldehyde/ketone 2,4 dinitrophenyl hydrazone derivative)

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13
Q

What can be used as a test to distinguish between aldehydes and ketones?

A
  • Fehling’s/Benedict’s reagent (changes to brick red for aldehydes, remains blue for ketones)
  • Tollen’s reagent (silver mirror formed with aldehydes, not with ketones)
  • potassium dichromate soln (changes to green for aldehydes, remains orange for ketones)
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14
Q

What is produced when an aldehyde is oxidised?

A

carboxylic acid

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15
Q

aldehyde + Fehlings ->

A

carboxylic acid + water

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16
Q

aldehyde + Tollens ->

A

carboxylic acid + ammonia + silver + water

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17
Q

aldehyde + acidified potassium dichromate ->

A

carboxylic acid + water + chromium ion (CR3+)

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18
Q

What is produced when an aldehyde is reduced?

A

primary alcohol

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19
Q

aldehyde + lithium aluminium hydride ->

A

primary alcohol

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20
Q

aldehyde + hydrogen cyanide ->

A

hydroxy nitrile

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21
Q

What conditions are required for Fehling’s?

A

alkali conditions

warming

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22
Q

What conditions are required for the reaction between a carbonyl compound and hydrogen cyanide?

A

pH 8

KCN present

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23
Q

What is produced when a ketone is reduced?

A

secondary alcohol

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24
Q

ketone + lithium aluminium hydride ->

A

secondary alcohol

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25
Q

What is produced when a ketone is oxidised?

A

nothing

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26
Q

ketone + hydrogen cyanide ->

A

hydroxy nitrile

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27
Q

How do you test for a methyl group adjacent to a carbonyl bond?

A

iodoform
-iodine in presence of an alkali
+ve result = yellow ppt (CHI3) and antiseptic smell

28
Q

Which aldehydes give a positive result for iodoform?

A

only ethanal

29
Q

Which ketones give a positive result for iodoform?

A

any ketone with its oxygen on its second carbon

30
Q

What happens in an iodoform reaction?

A
  • 3 hydrogen atoms on CH3 are substituted with 3 iodine atoms
  • the bond between the CI3 and the rest of the molecule is broken
31
Q

Which primary alcohols give a positive result for iodoform?

A

only ethanol

  • iodine oxidises ethanol to ethanal
  • ethanal then gives a positive result
32
Q

Which secondary alcohols give a positive result for iodoform?

A

any secondary alcohol with its OH on the second carbon

  • iodine oxidises it to a ketone with its oxygen on the second carbon
  • this then gives a positive result
33
Q

Which tertiary alcohols give a positive result for iodoform?

A

none

34
Q

Why are HCN and KCN both needed for the reaction between a carbonyl compound and KCN?

A
  • KCN provides CN- for the first step

- HCN provides H+ for the second step

35
Q

What are the melting and boiling points of carboxylic acids like?

A
  • higher than alkanes and alcohols as each carboxylic acid can form 2 H-bonds with another (alcohols can only form 1 H-bond and alkanes can only form London forces)
  • increase down homologous series (as they have more electrons so form stronger London forces)
36
Q

Are carboxylic acids soluble in water?

A

yes

  • can H-bond with water
  • solubility decreases down homologous series as alky chain length increases and interferes with the H-bonds
37
Q

What is the acidity of carboxylic acids like?

A

pH 3-4

-weak acids (partially ionise)

38
Q

How can carboxylic acids be prepared?

A
  • oxidation of alcohols
  • oxidation of aldehydes
  • hydrolysis of nitriles
39
Q

What conditions are required to prepare carboxylic acids by oxidising alcohols/aldehydes?

A
  • heat under reflux and distillation
  • sodium/potassium dichromate in excess
  • conc sulfuric acid
40
Q

What conditions are required to prepare carboxylic acids by the hydrolysis of nitriles?

A
  • heat under reflux and distillation

- water and hydrochloric acid (for acid hydrolysis)

41
Q

carboxylic acid + lithium aluminium hydride ->

A

primary alcohol

42
Q

carboxylic acid + sodium carbonate ->

A

salt + carbon dioxide + water

effervescence

43
Q

carboxylic acid + alcohol ->

A

ester + water

44
Q

carboxylic acid + phosphorus pentachloride ->

A

acyl chloride + hydrogen chloride gas + phosphoryl chloride

steamy fumes

45
Q

What is produced when a carboxylic acid is reduced?

A

primary alcohol

46
Q

acyl chloride + water ->

A

carboxylic acid + hydrogen chloride

steamy fumes

47
Q

acyl chloride + alcohol ->

A

ester + hydrogen chloride

steamy fumes

48
Q

acyl chloride + conc ammonia ->

A

amide + ammonium chloride

dense white smoke

49
Q

acyl chloride + amine ->

A

N-substituted amide + hydrogen chloride

steamy fumes

50
Q

What reactions do acyl chlorides readily undergo?

A

addition-elimination reactions

51
Q

What are the issues with using acyl chlorides?

A
  • very exothermic rxns

- produce toxic HCl gas (∴ use fume cupboard)

52
Q

What is a suitable alternative to using acyl chlorides and why?

A

acid anhydrides

  • good yield
  • quick rxns
  • by-product (carboxylic acid) can be sold
53
Q

Where does an ester’s carboxylate chain come from?

A

carboxylic acid

54
Q

Where does an ester’s alkyl chain come from?

A

alcohol

55
Q

Where does an ester’s bridging oxygen come from?

A

alcohol

56
Q

What are the melting and boiling points of esters like?

A

relatively low compared to respective alcohols/carboxylic acids
-no H-bonds

57
Q

What can esters be used for?

A
  • flavours

- scents (in perfumes, etc)

58
Q

What is the solubility of esters like?

A

not very soluble

-smaller esters are more soluble

59
Q

What is produced in the acid hydrolysis of esters?

A

carboxylic acid and alcohol

60
Q

What are the conditions of acid hydrolysis?

A
  • reflux

- dilute acid catalyst (eg. H2SO4 or HCl)

61
Q

What is produced in the base hydrolysis of esters?

A

carboxylate salt and alcohol

62
Q

What are the conditions of base hydrolysis?

A
  • reflux

- NaOH/KOH (base)

63
Q

How can a carboxylate salt (produced by the base hydrolysis of an ester) be extracted?

A

by using a dilute strong acid (eg. HCl) in excess

-because it’s insoluble

64
Q

Is the acid hydrolysis of an ester reversible or non-reversible?

A

reversible

∴ low yield

65
Q

Is the base hydrolysis of an ester reversible or non-reversible?

A

non-reversible

∴ high yield

66
Q

How can polyesters be produced by condensation polymerisation?

A

-condensation polymerisation of a diol and a dicarboxylic acid
or
-condensation polymerisation of a monomer containing both an alcohol and carboxylic acid group

Alevel Chemistry Edexcel (19 decks)

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