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N Chemistry A Level > Topic 17 Organic II > Flashcards

Topic 17 Organic II Flashcards

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1
Q

What are 2 types of isomerism?

A

structural
stereo

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2
Q

what are 3 types of structural isomerism?

A
  • chain
  • position
  • functional group
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3
Q

what are 2 types of stereoisomerism?

A
  • geometric
  • optical
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4
Q

What are optical isomers?

A
  • same molecular
  • same structural
  • different 3D spatial arrangement
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5
Q

what are conditions needed for geometric isomers?

A

double C=C bonds as it limits rotations

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6
Q

What are conditions needed for optical isomers?

A
  • must have chiral centre
    (usually C)
  • Has 4 (or more) different groups bonded to it
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7
Q

What does nonsuperimposable mean?

A

Like hands
have the same properties and structure
but are mirror images of each other

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8
Q

What can make a racemic mixture?

A
  • SN1 (sometimes)
  • MUST have chiral centre
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9
Q

No rotation when plane polarised light is shown through…

A

think RACEMIC MIXTURE
For sure

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10
Q

what is the only difference between enantiomers?

A

rotate plane polarised (monochromatic) light in equal but opposite directions

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11
Q

why do enantiomers rotate monochromatic lights in different directions?

A

due to their different arrangements of atoms in space

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12
Q

why must it be racemic mixtures when there are no rotations through polarised light?

A

enantiomer rotations cancel out

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13
Q

How are enantiomers / racemic formed?

A

50/50 chance for SN1 attack of chiral centre (from above or below trigonal planar plane)
other bonds pushed up or down when new bond formed
forming enantiomers in equal portions

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14
Q

What can be used to test for carbonyls?

A
  • dichromate
  • Benedict’s/fehlings
  • tollens (ammoniacle silver nitrate)
  • Lithium aluminium hydride (LiAlH4)
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15
Q

What is dichromate’s reaction to carbonyls? +why?

A

Aldehyde: Orange to green as aldehyde is oxidised to -COOH
Ketone: remain orange, no change

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16
Q

Can ketones be oxidised or reduced? How?

A

Only reduced
By LiAlH4 in dry ether

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17
Q

What is the Benedict’s/Fehling’s reactions to carbonyls?

A

Aldehydes: Blue to brick red as they get oxidised
Cu 2+ + Aldehyde -> Cu3+
No change in ketones

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18
Q

Aldehyde + alkaline oxidising agent ->

A

Carboxylate + water

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19
Q

How to turn carboxylate into carboxylic acid?

A

Add strong acid
To Protonate into carboxylic acid

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20
Q

What is tollens reagent’s reaction to carbonyls?

A

Aldehydes: Silver mirror formed - Ag (s) from Ag+
No change in ketone

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21
Q

What does LiAlH4 stand for?

A

Lithium aluminium hydride

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22
Q

What is LiAlH4’s reactions to carbonyls?

A

In dry ether
Acts as reducing agent - [H]
Aldehyde + [H] → 1° alcohol
Ketone + 2[H] → 2° alcohol

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23
Q

What is the the reaction equation of Fehling’s solution with aldehyde? And explain colour change

A

2 Cu2+ (aq) + 2OH- (aq) + 2e- -> Cu2O (s) + H2O (l)
Hence blue -> red

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24
Q

What is tollen’s reagent’s reaction with aldehyde? Give equation
And what change is observed?

A

2Ag+ (aq) + 2OH- (aq) -> Ag2O (s) + H2O (l)

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25
Q

Why can’t tertiary alcohols or ketones be oxidised?

A

They must have an H atom bonded to C to be oxidised

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26
Q

What is [H]?

A

Reducing agent

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27
Q

What is formed when carbonyls + HCN?

A

hydroxy nitrile

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28
Q

What does HCN stand for and is it a strong or weak acid?

A

Hydrogen cyanide
Weak

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29
Q

What catalyst can be added to the carbonyl + HCN reaction to speed up RoR?

A

KCN (salt)
It provides loads of cyanide nucleophiles
(In this case conc of catalyst impacts RoR)

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30
Q

Are carboxylic acids strong or weak acid?

A

Weak

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31
Q

How to test for carboxylic acids?

A

Add sodium carbonate (Na2CO3 / NaHCO3)
- fizzing to indicate CO2 produced

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32
Q

What’s the best indicator to use to test for carboxylic acids?

A

Universal indicator
Or pH probe

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33
Q

How soluble is carboxylic acids in water? Why?

A
  • very!
  • when R group is small, H bonds can form
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34
Q

Does solubility for carboxylic acids increase or decrease as chain length increases? Why?

A

Carb. aciDDDDs so DDDDecreases
As non polar part of molecule is more significant

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35
Q

What’s a dimer in terms of carboxylic acids

A

2 of them bonded together covalently
Therefore explains high mp/bp

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36
Q

What are 3 methods to make carboxylic acids?

A
  1. Distill 1° alcohol with [O] like K2Cr2O7
  2. Reflux 2° alcohol with [O]
  3. Hydrolysis of nitriles
37
Q

What are 2 methods of hydrolysis of nitriles to make carboxylic acids?

A

+ water
1. Acid catalysed
2. Alkali catalysed, makes carboxyLATE then protonate by adding strong acid

38
Q

How to make carboxylic acids via hydrolysis using acids?

A

nitrile + water -H+—> carboxylic acid + ammonium

39
Q

How to make carboxylic acids using nitriles and alkali?

A

Nitrile + water + OH- —> carboxyLATE + ammonia
Then protonate by adding STRONG acid to make

40
Q

How to turn carboxylic acid into aldehyde?

A

+ dry ether and reflux in LiAlH4
+ dilute acid
makes 1° alcohol
+ oxidising agent
into aldehyde

41
Q

what are examples of good bases?

A

metal oxides/hydroxide/carbonates/hydrogencarbonates
ammonia/ammonium hydroxides

42
Q

What does monoprotic mean in terms of -COOH?

A

they make salt and water when reacted with bases

43
Q

what does PCl5 test for?

A

-OH groups

44
Q

PCL5 + -COOH ->

A

RCOCl + HCl (g) + POCl3
white misty fumes (HCl)
-oyl chloride
- v rigorous reaction

45
Q

carboxylic acid + alcohol (+ H+) ⇌

A

ester + water
e.g. ethyl methanoate

46
Q

what is the ester functional group?

A

O – C = O

47
Q

what is the acyl chloride functional group?

A

Cl – C = O
COCl

48
Q

how to make acyl chlorides?

A

PCl5 + RCOOH

49
Q

are acyl chlorides reactive and why?

A

v reactive
since the C is more δ+ (than in -COOH)
it is bonded to two v δ- atoms
pulling e- density away
therefore very easily attacked by nucleophiles

50
Q

acyl chloride + water →
in what conditions?

A

HCl + carboxylic acid
keep acyl chloride in DRY ether as v reactive

51
Q

acyl chloride + alcohol →
what kind of reaction is it?

A

ester + HCl
condensation & exothermic reaction

52
Q

what are 2 methods of making esters?

A

-COCl + -OH
-COOH + -OH

53
Q

compare the 2 ways of making esters

A

using COCl / COOH, both + -OH
goes to completion / doesnt
no heating / lots of energy needed to heat
corrosive products / not

54
Q

acyl chloride + ammonia →

A

ammonium chloride + amide
NH4Cl + R-C(=O)(-NH2)

55
Q

what is observed when acyl chloride + ammonia?

A

white smoke from NH4Cl

56
Q

acyl chloride + 1° amine →

A

2° amine + HCl
e.g. N-methylethanamide

57
Q

acyl chloride + 2° amine →

A

3° amine + HCl
e.g. N,N-disubstitutedamide

58
Q

acyl chloride + 3° amine →

A

does not react
as no H on N atom to make HCl

59
Q

amine vs amide?? (functional groups)

A

amine: -NH2
amide: -C(=O)(-NH2)

60
Q

ester + water →/⇌

A

carboxylic acid + alcohol
→ in general
⇌ when acid catalysed and heat

61
Q

ester + hydroxide →

A

carboxylate + alcohol
OH- is not a reactant! and alkaline not reversible.

62
Q

Compare methods of esterification between RCOCl and RCOOH

A

With RCOCl / RCOOH
- reaction is irreversible / reversible
- HCl is by product / water
- reaction is very fast, acid catalyst not needed / slower, need acid catalyst

63
Q

Do carbonyls or alcohol have higher or lower mp/bp (same number of C)
Why?

A

Carbonyls have much lower mp/bp
As no H bonds
So fewer e-s

64
Q

What is 2,4-DNPH reaction to carbonyls?

A

Orange to bright yellow ppt

65
Q

How to identify exact carbonyl with 2,4-DNPH?
(3 marks)

A

Filter bright yellow ppt from positive result
Recrystallise
Melt purified solid
Mp will tell identity of carbonyl

66
Q

How to tell if 2,4-DNPH ppt is aldehyde or ketone?

A

If can be oxidised = aldehyde

67
Q

Iodine in presence of alkali

A

triiodomethane (CHI3) reaction can be used to identify the presence of a CH3CO group in aldehydes and ketones.

68
Q

What is triiodomethane formula and what does it smell like?

A

CHI3
Hospitals

69
Q

When can alkaline iodine + carbonyl/alcohol react?
What is formed?

A

Have CH3CO group
Forms bright yellow ppt CHI3

70
Q

How to balance equation of iodine in presence of alkali

A

One organic
3 of everyone else
One extra NaOH

71
Q

Define isomerism

A

Molecules with same molecular formula
But atoms are bonded in different ways to produce different compounds with different chemical and physical properties

72
Q

Define chiral centre

A

An atom (often carbonyl with 4 diff groups bonded to it

73
Q

Define structural isomer

A

Molecules w same molecular formula but different structural formulas

74
Q

Define stereoisomerism

A

Molecules w same molecular and structural formula
But diff 3D arrangement of atom

75
Q

Which ONE test tests for carbonyls?

A

2,4-DNPH

76
Q

What organic compound smells like pineapples?

A

Esters
(If in doubt, go for esters)

77
Q

What are the nomenclature 1-10

A

Meth Eth prop but pen hex hept oct non dec

78
Q

Instead of saying Brady’s reagent, what is it’s official name? and what does it test for?

A

2,4-DNPH
carbonyls
( - must have CH3CO group to react with iodine)
into bright yellow ppt

79
Q

when propanone reacts with iodine in the presence of NaOH, the crystalline solid product has the formula…
What does it look like?

A

CHI3
triiodomethane
pale yellow

80
Q

What conditions are needed to make racemic mixtures?

A

has chiral centre
w 4 different groups bonded to it

81
Q

what is a molecular formula?

A

formula of compound but no structural info
e.g. C5H12O - could be an alcohol or ketone

82
Q

An alcohol can be converted into a ketone by oxidation.
Explain why refluxing the mixture first, rather than immediately distilling the product over from the beginning results in higher yield of ketone.
(1 mark)

A
  • so no volatile alcohol reactant will be lost
  • ensure all alcohol oxidises
83
Q

explain in terms of intermolecular forces in liquids why bp is
ethanal < ethanol < ethanoic acid
(3 marks)

A
  • ethanoic has the most e-s so most london forces
  • both ethanol and ethanoic acid can form H bonds between itself
  • ethanoic acid can form dimers covalently
  • so most energy needed to overcome
84
Q

Why is KCN necessary to form hydroxynitriles with HCN + aldehyde? (1 mark)

A

KCN fully ionises to produce loads of CN- nucleophiles
so RoR increases

85
Q

explain why the hydroxynitrile is not optically active. (2 marks)

A

The CN- nucleophile can attack trigonal planar with equal probability from above and below to form enantiomers
forming racemic mixture
each rotates pp light in equal but opp directions so they cancel out

86
Q

what does optically active mean?

A

capability of rotating the plane of vibration of polarized light to the right or left

87
Q

what are the 2 types of reactions to form a polymer?

A

condensation
or
addition (alkenes)

88
Q

how are esters formed?

A

between 2 OH ends of molecule

N Chemistry A Level (21 decks)

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