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Chemistry Edexcel A Level > Topic 17 Organic II > Flashcards

Topic 17 Organic II Flashcards

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
Or Non chiral molecules
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? WHY?

A

Aldehydes: Blue to brick red ppt
Cu 2+ + Aldehyde -> Cu2O (Cu2+ is reduced)
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+ , Ag+ reduced
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
Why can’t tertiary alcohols or ketones be oxidised?
They must have an H atom bonded to C to be oxidised
26
What is [H]?
Reducing agent
27
What is formed when carbonyls + HCN?
hydroxy nitrile
28
What does HCN stand for and is it a strong or weak acid?
Hydrogen cyanide Weak
29
What catalyst can be added to the carbonyl + HCN reaction to speed up RoR?
KCN (salt) It provides loads of cyanide nucleophiles (In this case conc of catalyst impacts RoR)
30
Are carboxylic acids strong or weak acid?
Weak
31
How to test for carboxylic acids?
Add sodium carbonate (Na2CO3 / NaHCO3) - fizzing to indicate CO2 produced
32
What’s the best indicator to use to test for carboxylic acids?
Universal indicator Or pH probe
33
How soluble is carboxylic acids in water? Why?
- very! - when R group is small, H bonds can form
34
Does solubility for carboxylic acids increase or decrease as chain length increases? Why?
Carb. aciDDDDs so DDDDecreases As non polar part of molecule is more significant
35
What’s a dimer in terms of carboxylic acids
2 of them bonded together covalently (=O - - - HO-) Therefore explains high mp/bp than expected
36
What are 4 methods to make carboxylic acids?
1. Reflux 1° alcohol with [O] like K2Cr2O7 2. Hydrolysis of nitriles (add dil acid or alkali) 3. Hydrolysis of RCOCl (add water)
37
What are 2 methods of hydrolysis of nitriles to make carboxylic acids?
+ water 1. Acid catalysed 2. Alkali catalysed, makes carboxyLATE then protonate by adding strong acid
38
How to make carboxylic acids via hydrolysis using acids?
nitrile + water -H+—> carboxylic acid + ammonium
39
How to make carboxylic acids using nitriles and alkali?
Nitrile + water + OH- —> carboxyLATE + ammonia Then protonate by adding STRONG acid to make
40
How to turn carboxylic acid into aldehyde?
+ dry ether and reflux in LiAlH4 + dilute acid makes 1° alcohol + oxidising agent into aldehyde
41
what are examples of good bases?
metal oxides/hydroxide/carbonates/hydrogencarbonates ammonia/ammonium hydroxides
42
What does monoprotic mean in terms of -COOH?
they make salt and water when reacted with bases
43
what does PCl5 test for?
-OH groups
44
PCL5 + -COOH ->
RCOCl + HCl (g) + POCl3 white misty fumes (HCl) -oyl chloride - v rigorous reaction
45
carboxylic acid + alcohol (+ H+) ⇌
ester + water e.g. ethyl methanoate
46
what is the ester functional group?
C = O | O
47
what is the acyl chloride functional group?
Cl – C = O COCl
48
how to make acyl chlorides from carboxylic acids?
+ PCl5
49
are acyl chlorides reactive and why?
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
acyl chloride + water → in what conditions?
HCl + carboxylic acid keep acyl chloride in DRY ether as v reactive
51
acyl chloride + alcohol → what kind of reaction is it?
ester + HCl condensation & exothermic reaction
52
what are 2 methods of making esters?
-COCl + -OH -COOH + -OH
53
compare the 2 ways of making esters
using COCl / COOH, both + -OH goes to completion / doesnt no heating / lots of energy needed to heat corrosive products / not
54
acyl chloride + (excess) ammonia →
If excess, ammonium chloride + amide NH4Cl + R-C(=O)(-NH2) If not excess, HCl + amide
55
what is observed when acyl chloride + ammonia?
white smoke from NH4Cl
56
acyl chloride + 1° amine →
2° amine + HCl e.g. N-methylethanamide
57
acyl chloride + 2° amine →
3° amide + HCl e.g. N,N-disubstitutedamide
58
acyl chloride + 3° amine →
does not react as no H on N atom to make HCl
59
amine vs amide?? (functional groups)
amine: -NH2 amide: -C(=O)(-NH2)
60
ester + water →/⇌
carboxylic acid + alcohol → in general ⇌ when acid catalysed and heat
61
ester + hydroxide →
carboxylate + alcohol OH- is not a reactant! and alkaline not reversible.
62
Compare methods of esterification between RCOCl and RCOOH
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
Do carbonyls or alcohol have higher or lower mp/bp (same number of C) Why?
Carbonyls have much lower mp/bp As no H bonds And fewer e-s
64
What is 2,4-DNPH reaction to carbonyls?
Orange to bright yellow ppt
65
How to identify exact carbonyl with 2,4-DNPH? (3 marks)
**Filter** bright yellow ppt from positive result **Recrystallise** Melt purified solid **Mp** will tell identity of carbonyl
66
How to tell if 2,4-DNPH ppt is aldehyde or ketone?
If can be oxidised = aldehyde
67
What is Iodine in presence of alkali used to test
triiodomethane (CHI3) reaction can be used to identify the presence of a CH3CO group in aldehydes and ketones.
68
What is triiodomethane formula and what does it smell like?
CHI3 Hospitals
69
When can alkaline iodine + carbonyl/alcohol react? What is formed?
Have CH3CO group Forms bright yellow ppt CHI3
70
How to balance equation of iodine in presence of alkali
One organic 3 of everyone else One extra NaOH RCOCH3 + 4NaOH + 3I2 -> RCOONa + HCI3 + 3H2O + 3NaI
71
Define isomerism
Molecules with same molecular formula But atoms are bonded in different ways to produce different compounds with different chemical and physical properties
72
Define chiral centre
An atom (often carbonyl with 4 diff groups bonded to it
73
Define structural isomer
Molecules w same molecular formula but different structural formulas
74
Define stereoisomerism
Molecules w same molecular and structural formula But diff 3D arrangement of atom
75
Which ONE test tests for carbonyls?
2,4-DNPH
76
What organic compound smells like pineapples?
Esters (If in doubt, go for esters)
77
What are the nomenclature 1-10
Meth Eth prop but pen hex hept oct non dec
78
Instead of saying Brady's reagent, what is it's official name? and what does it test for? What are the conditions and result?
2,4-DNPH carbonyls ( - must have CH3CO group to react with iodine) into bright yellow ppt
79
when propanone reacts with iodine in the presence of NaOH, the crystalline solid product has the formula... What does it look like?
CHI3 triiodomethane pale yellow
80
What conditions are needed to make racemic mixtures?
has chiral centre w 4 different groups bonded to it
81
what is a molecular formula?
formula of compound but no structural info e.g. C5H12O - could be an alcohol or ketone
82
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)
- so no volatile alcohol reactant will be lost - ensure all alcohol oxidises
83
explain in terms of intermolecular forces in liquids why bp is ethanal < ethanol < ethanoic acid (3 marks)
- 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
Why is KCN necessary to form hydroxynitriles with HCN + aldehyde? (1 mark)
KCN fully ionises to produce loads of CN- nucleophiles so RoR increases
85
explain why the hydroxynitrile is not optically active. (2 marks)
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
what does optically active mean?
capability of rotating the plane of vibration of polarized light to the right or left
87
what are the 2 types of reactions to form a polymer?
condensation or addition (alkenes)
88
how are esters formed?
between 2 OH ends of molecule
89
Give a reason why 3-methylbutanoic acid cannot be formed from oxidising 3-butan-2-one from 3-methylbutan-2-ol.
Ketones cannot be further oxidised Only primary alcohols can be oxidised to carboxylic acid.
90
State what it is meant by chiral. (1 mark)
Forms 2 superimposable isomers / Has 4 different groups attached to it
91
If something reacts with carbonates to produce CO2, what does it have to be?
An acid! (as water and salt also formed)
92
What reaction involves nucleophilic addition?
ALDEHYDE OR KETONE + HCN + KCN MAKES RCNOH
93
Biodegradable polyesters break down naturally. State why this is an advantage. (1 mark)
- waste does not accumulate and occupy landfill
94
Using the apparatus for distillation instead of reflux is not an efficient way to produce ethanoic acid from ethanol. Explain why. (2 marks)
- ethanol would be formed instead of ethanoic acid - as ethanol has **lower bp** , more volatile

Chemistry Edexcel A Level (24 decks)

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