Topic 6 Organic Chemistry Flashcards
(126 cards)
1
Q
Why are alcohols ‘good’ fuels?
A
- easy to transport
- easy to store
- very exothermic combustion (completely)
2
Q
How can ethanol be made?
A
- fermentation
- from ethene (+ steam using H3PO4 catalyst)
- SN of halogenoalkane
3
Q
What is halogenation?
A
Replacing Hydrogen with halogen
E.g. Making halogenoalkane from alcohol
4
Q
How to test for Alkene?
A
Bromine water from orange to colourless
5
Q
What is stereoisomerism?
A
Molecules that have the same molecular formula and the same structural formula, but have different 3D shape
6
Q
What isomerism can Alkenes have?
A
Geometric isomerism
7
Q
Why can some alkenes have geometric isomerism?
A
Because of the C=C bond, they must have 2 diff groups bonded to them
8
Q
What is the E/Z nomenclature system?
A
Zame Zide of high priority groups (w highest number of atomic num)
E is opposite sides
9
Q
Combustion of alkenes
Compare result with corresponding alkane
A
Alkene + oxygen -> water + carbon dioxide
Alkenes are more likely to burn with sootier flames than corresponding alkane
(Bcs of lower C:H ratio)
10
Q
What is an addition reaction?
A
2+ reactants in 1 product
11
Q
What is an electrophile?
A
Small species that can accept a pair of electrons / attracted to area of high e- density
Either has positive charge or δ+
12
Q
Why do alkenes react with electrophiles?
A
Because alkenes have a pair of e- in a π bond (of C=C)
Has High electron density
Which can form a bond to electrophile
13
Q
Why will alkenes readily react in addition reactions?
A
π bonds are weak and sticks out
14
Q
What is hydrogenation?
A
Adding hydrogen to an alkene, forming corresponding alkane
15
Q
What condition and reactant does hydrogenation must take place in?
(Alkene -> alkane)
A
Add Hydrogen
Ni catalyst 150 C
Or
Pt catalyst RTP
16
Q
Why is hydrogenation an important reaction?
A
So margarine can be made from oils
17
Q
Alkene + Halogen -> ?
A
Dihalogenoalkane
18
Q
What conditions needed to make dihalogenoalkane from Alkene and halogen?
A
Mix and shake
19
Q
Alkene + hydrogen halide -> ?
A
Halogenoalkane
20
Q
What is Markovnikoff’s rule?
A
Hydrogen will be more attracted to the C atom with most H attached to it already (in a C=C bond)
21
Q
Alkenes + steam -> ?
A
Alcohol
22
Q
Why does Markovnikoff’s rule happen?
A
The greater number of alkyl group, the most stable the carbocation is most likely to form
23
Q
What carbocation is least stable?
A
1° primary
24
Q
What carbocation is most stable?
A
3 °
25
What conditions are required for alkenes + steam to form alcohol?
H3PO4 phosphoric acid
at 300°C
60 atm
26
Alkene + Br2 (aq) ->
Bromoalcohol !!! + HBr
27
What is needed to oxidise alkenes into diols?
H2SO4 and KMnO4
Sulfuric acid and potassium manganate
28
Alkene + [O] + H2O -> ?
Diol
29
What reagent and conditions are needed to make Diol from oxidising alkene?
KMnO3
H2SO4 heat under reflux
30
What colour is potassium manganate
Purple
31
Why can alkenes polymerise?
Bcs of π bonds that break and σ bonds form between C and monomer units
32
What are the 2 types of polymerisation?? And what is added?
Condensation (when water is a byproduct)
Free radical addition, add free radical initiator (no byproducts)
33
What is the general equation for cycloalkane?
CnH2n
34
What are the 4 steps of free radical substitution?
Initiation
Propagation 1
Propagation 2
Termination
35
What is the initiator for halogens?
UV light
36
how to convert halogenoalkane to alkene? what conditions and reagent required?
conc KOH or NaOH
ethanol and heat
37
what reagent and condition needed to form nitrile from halogenoalkane? Why is it useful for organic chemistry?
KCN / NaCN , heat under aq ethanol solution
increases C chain length
38
What is a reagent?
Reactant’s Name on the bottle
39
What is the reagent to oxidise alcohol?
Potassium or Sodium
Dichromate Cr2O7^2-
Orange to green if positive
+ H2SO4
40
What does PCl5 test for
-OH group
Alcohol or carboxylic acid
(Also chlorination)
41
How to test for primary secondary or tertiary alcohol?
Oxidising
- reflux it
See what products it makes
42
How to eliminate/dehydrate alcohol? What does it make?
Use conc. sulfuric H2SO4 or phosphoric acid H3PO4
Make alkenes and water
43
What are 2 methods of chlorination?
Add conc HCl
Or
Add PCl5
44
What is PCl5 used for? What does positive result look like?
Test for -OH groups (water, alcohol and carboxylic acid)
White misty fumes
45
What are 2 methods of bromination?
50% conc H2SO4 +NaBr making HBr + NaHSO4
Alcohol + HBr -> Bromoalkane + water
Or
Damp red phosphorus with bromine to make PBr3
46
Why 50% conc H2SO4 for bromination?
Trying to make HBr, prevent redox reaction forming other unwanted products
47
How to iodination to make iodoalkane?
Reagents
- damp red phosphorus
- iodine
P + 1.5 I2 -> PI3
Add this to alcohol to make iodoalkane
48
What colour is dichromate?
Orange
49
What is a reagent?
Name on the bottle
50
2 types of reagents needed to oxidise alcohol?
K/Na dichromate (Cr2O7 2-)
Sulfuric acid H2SO4 (H+)
51
What is formed when oxidising primary alcohols using distillation?
Aldehyde + water formed
52
What is formed when oxidising primary alcohol via reflux?
Carboxylic acid and water formed
53
How is oxidation written in organic chemistry?
[O]
54
How to oxidise secondary alcohols? What is produced?
Reflux or distill
Ketone + water produced
55
What is formed when refluxing / distilling tertiary alcohol?
No reaction
Since no H can be removed
So cannot be oxidised
56
What’s a carbonyl?
Aldehyde + ketone
=O bond in middle of C chain
57
What colour is manganate?
Purple
58
What does MnO4- + H2SO4 oxidise? What colour does it turn from and to?
Alkenes, alcohols and aldehydes
Purple to colourless
59
What does Cr2O7 2- + H2SO4 oxidise? What colour does it change from and to?
Alkenes, alcohols and aldehydes
Orange to green
60
How to dehydrate alcohols? (What reagent is used?)
Conc H3PO4
phosphoric acid
(OR conc sulfuric acid H2SO4)
61
What is formed from dehydrating an alcohol?
Alkene + water
62
Does miscibility/solubility increase or decrease as alcohol chain length increases? Why?
Decreases bcs C:OH ratio decreases
Greater C chain is more non polar, so becomes less soluble (less interaction between OH and water, cannot form H bonds)
Bigger molecules take up more space, more non-polar proportion to polar
63
Does viscosity increase or decrease as alcohol chain length increases?
Increase bcs number of London Forces increases
64
Does bp increase or decrease as alcohol chain length increases?
Increase as more e- means more London forces which takes more energy to break
65
Does corresponding alcohol or alkane have a higher mp/bp?
Alcohol is much higher since have more e-s so more London forces
And alcohol have H bonds, alkanes don’t
66
What’s an aldehyde?
=O at the end of C chain
67
Halogenoalkane + ammonia (NH3) ->
What conditions needed?
-> Amine + HX
AND -> Amine + NH4X
- Excess NH3 (so only get 1 substitution)
- dissolved in ethanol!!
- heat in sealed tube
68
What is the functional group of amine?
-NH2
69
Halogenoalkane + OH- (eth) ->
Alkene + H2O + X-
(Only if there is adjacent H atom)
Using ethanol solvent, with reagent NaOH or KOH
Heat under reflux
70
Halogenoalkane + OH- (aq) ->
(+ what mechanisms used?)
Alcohol + halide
Either SN 1 (3° or 2°)
SN2 (1°)
71
What is a nucleophile?
Has lone pair
72
What is a nucleophilic substitution reaction and 2 examples?
Attacking δ+ (positive) and replacing the bond with something δ-
SN1 or SN2
73
What do you call CH3CH2CH2(NH2)
amino propane
74
What do you call CH3C≡N
methane nitrile
75
Ag+ + X- ->
What is it used for?
AgX (s)
Precipitate show presence of halides
76
What are the AgX precipitate colours?
What further testing to identify each halide?
Chlorine - white (soluble in both dil and conc NH3)
Bromine - cream (only in conc)
Iodine - yellow (neither)
77
What reaction is Halogenoalkane + OH- (eth) ?
Elimination (coz C=C is made)
As a base not a nucleophile
REFLUX
78
Why does F have the strongest bond enthalpy in G7?
Smallest ion
So smallest atomic radius
So stronger attraction
79
What does Fehling’s solution test for? In what conditions?
Ketones (stays blue) or aldehydes (turns red)
In warm water bath
80
What’s the difference between cis/trans and E/Z classification?
cis/trans must have identical groups attached to diff sides of alkene (at least 2 repeating)
E/Z could have 4 diff groups
81
Devise an experiment to compare rate of Halogenoalkane hydrolysis (6 marks)
- add ethanol as solvent (so it dissolves and reacts with water)
- fair test (equal volume and temp)
- add silver nitrate
- record time taken for ppt to form
- iodoalkane should be the fastest, chloroalkane slowest - due to bond enthalpies for C-I
82
Why is ethanol added for hydrolysis of Halogenoalkane?
So reactants are more miscible/soluble
As Halogenoalkanes are insoluble in water
83
Why are test tubes left in 50 C water bath for Halogenoalkane hydrolysis?
To allow reactions to equilibriate
84
What is the reagent to make nitriles? What’s the advantage?
Potassium cyanide KCN
Increase carbon chain length
85
Why is it heated in a sealed container when making amine from Halogenoalkane? 2 marks
Increase RoR
No sealed tube results in loss of ammonia
86
What is the rate of hydrolysis of primary secondary and tertiary Halogenoalkane?
3 ° > 2 °> 1 °
Most stable is tertiary carbocation so easier to lose the halide
87
Structural isomer vs stereoisomers?
Structural: have the same molecular formula but a different bonding arrangement among the atom
Stereoisomers: have identical molecular formulas and arrangements of atoms. They differ in 3D structure
88
What alcohol cannot be oxidised?
Tertiary alcohol
No change in reaction
89
What is a structural isomer? 2 marks
Same molecular formula
But different structural formula
90
What is the purpose of condensers when hydrolysing Halogenoalkane?
Prevent loss of reactants
91
What is used to test for butan-1-ol and what’s the expected observation?
Phosphorus(V)chloride PCl5
White Misty fumes
Because it Has -OH group
92
Why can't tertiary haloalkanes do SN2?
due to steric hinderance
93
Why can't primary halogenoalkanes do SN1?
too unstable
94
What reagent is used to eliminate Halogenoalkane?
conc NaOH/KOH
Aka OH- (eth)
REFLUX
95
What is the **classification** of a Halogenoalkane or alcohols?
Primary secondary or tertiary
96
What are 2 chemicals used to make ethanal from ethanol?
H2SO4
K2Cr2O7
97
What’s the issue with SO2?
Dissovles in raindrops and makes acid rain
98
What is CFC (chlorofluorocarbons)’s properties?
- greenhouse gas
- damage ozone layer
- excellent refrigerant
- inflammable (man inhaled it)
99
Why are the conc H2SO4 and K2Cr2O7 added a drop at a time in the lab process?
Control rate of reaction to prevent exothermic reaction from overheating and exploding
100
What is the systematic name of CF2ClBr?
bromo chloro difluoro methane
101
Why are halogenoalkanes very good for putting out fires? 2 marks
- non flammable, unreactive
- v dense so smother and displace O2
102
why are HCFCs better than CFCs?
CFCs reach upper atmosphere and react, creating radicals
damage Ozone layer
HCFCs dont reach upper atmosphere bcs less reactive, so no damage to Ozone layer
103
How to differentiate carboxylic acid from aldehyde produced for primary alcohols?
Add carbonate (e.g. Na2CO3)
Effervescence since H+ ions react to produce CO2
104
How to separate 2 substances?
- separating funnel
- simple distillation
- fractional distillation
- drying agent to remove water eg calcium chloride
105
How to use separating funnel?
You want the top layer
Overrun bottom layer
Repeat a few times
Run upper layer into another flask
106
Why is incineration a bad method for disposal of poly(chloroethene)? 2 marks
HCl produced
Very toxic fumes
107
What type of reaction is hydrogenation?
Reduction
108
Explain why Markovnikoff’s rule happen
More alkyl groups = more electron pushing
So carbocations more likely to form
H attracted to C with more H bonded to it already
109
Are carboxylic acids strong or weak acids?
Weak
110
How do chemists limit the problems caused by polymer disposal?
- develop biodegradable polymers
- remove toxic waste gases caused by incinerating plastics
111
What is the reaction mechanism when ethane and chlorine react in UV light?
Free radical substitution
112
What is structural and displayed formula?
Structural is like CH3CH2CH2CH3
but displayed is when you draw it outttttttt
113
Give one ad and disad for incinerating polystyrene. (2 marks)
Ad: releases energy / avoids landfill
Disad: releases toxic fumes
114
Explain how oxides of Sulfur and nitrogen can be formed from the combustion of fossil fuels. (2 marks)
- Sulfur compounds / impurities
- react with oxygen in air
OR
- nitrogen in air
- react w oxygen in air
115
Draw dot cross diagram for Sulfur dioxide. (1 mark)
One oxygen is dative from S
Double bond with other oxygen
Lone pair in S
116
A student suggested that to synthesise (Z)-2-chloropent-2-ene, chlorine could be added to (Z)-pent-2-ene in the presence of UV light.
Give 3 reasons why this method is unlikely to produce desired product (Z)-2-chloropent-2-ene. (3 marks)
- hard to control reaction- Cl atom can substitute to any Carbon
- likely to produce poly chlorinated product
- (Z)-pent-2-ene would form (E) isomer not Z
117
How is the ethanol formed by the hydration of ethene classified?
fossil fuel
and
non renewable
as obtained from catalytic cracking
118
Which mechanism would tertiary haloalkane react with NaOH(aq) and why? (3 marks)
- SN1
- because 3° carbocation will readily form when C-X bond breaks
- as very stable with 3 e- pushing alkyl groups
- also have steric hinderance so cant SN2
119
What is an advantage of incineration? (1 mark)
Avoids landfill
120
State and explain how the rate of reaction of a halogenoalkane would differ with sodium hydroxide to that with water. (2 marks)
- Rate of reaction with NaOH is faster because OH- ions are negative.
- Stronger nucleophile
121
if NaOH is used to hydrolyse the halogenoalkane, state and explain why adding silver nitrate to a sample of a halogenoalkane that has been hydrolysed with sodium hydroxide would not indicate the identity of the halogen present in the halogenoalkane. (2 marks)
AgOH, a white solid form.
Masking the colour of silver halide.
122
Is forming free radicals with UV heterolytic or homolytic fission?
HOMOLYTIC
123
2-bromobjtand can react with OH-(aq) by SN1 mechanism.
Explain why the butan-2-ol produced from a single optical isomer of 2bromobutane, using this mechanism, is not optically active. (3 marks)
Forms racemic mixture
Intermediate is trigonal planar shape
So equal probability to be attacked by nucleophile
124
Give 3 ways where waste polymers can be utilised to improve their sustainability. (3 marks)
- recycle
- incinerate to GENERATE ELECTRICITY
- use as feedstock, breakdown into monomers
125
What are the products of homolytic and heterolytic fission?
Homolytic - free radicals
Heterolytic - ions
126
Compare and contrast the acid and alkali hydrolysis for the same ester. (4 marks)
Both form the same alcohol
Ac/Alk
Reversible / not
Forms carboxylic acid / forms carboxylate
Acts as catalyst / acts as reactants
