Paper 3A Part 2 Flashcards
1
Q
.If the compound doesn’t have a OH bond directly but still has an OH group it is classed as an ______, not a ______
A
alcohol, not a phenol
2
Q
.Phenol is less soluble in water than alcohols, why?
A
due to its non-polar benzene ring
3
Q
When dissolved in water, phenol partially dissociates to form what?
A
a phenoxide ion and a proton
4
Q
As phenol only partially dissociates it is ______, other phenols also act as ________
A
a weak acid (pH4-6)weak acids
5
Q
.Ethanol doesn’t react with sodium hydroxide (strong ___) or sodium carbonate (weak ___)
A
basebase
6
Q
Phenols and carboxylic acids will react with ____________________ (like aqueous sodium hydroxide)
A
solutions of strong bases
7
Q
carboxylic acids are strong enough to react with a weak base like sodium carbonate, you would observe what?
A
a gas/bubbles
8
Q
Draw the mechanism for phenol and sodium hydroxide
A
check notes or internet
9
Q
Draw the mechanism for phenol and sodium
A
check notes or internet
10
Q
Describe the bromination of phenols?
A
.Phenol reacts with aqueous solution of bromine (bromine water) .A halogen carrier is not required and the reaction can be carried out at room temperature
11
Q
Draw the mechanism of phenol and Br2
A
Check notes or internet
12
Q
What does the bromination of phenol look like?
A
This reaction decolourises bromine water and forms a white precipitate
13
Q
Why does phenol react more readily with bromine than benzene?
A
.One of the lone pairs of electrons on the p orbital of the O atom in the OH is partially delocalised into the ring.This increases the electron density.The electrophile becomes more polarised
14
Q
Describe the nitration of phenol
A
.Phenol readily reacts with dilute nitric acid at room temperature.It does not need halogen carrier.Makes with 2-nitrophenol or 4-nitrophenol and water
15
Q
Draw the nitration of phenol mechanism
A
check notes or internet
16
Q
Many aromatic compounds can undergo a second substitution, what is this called?
A
a di-substitution
17
Q
What is the directing effect?
A
The presence of substituted groups on a benzene ring will have an effect on the substitution of further groups – this is known as the directing effect
18
Q
Substituted groups can be classified by the effect they have on the electron density of the ring, what are the classifications?
A
- Electron donating – increases the electron density- Withdrawing electrons – decrease electron density
19
Q
What are electron donating substitition groups also known as, why?
A
.Side chains that increase electron density allow electrophiles to react faster than with benzene, so are ‘activating’ products
20
Q
Give an example of an electron donating substitution group
A
.OH – O lone pair orbitals overlap with delocalised ring.NH2 – N lone pair orbitals overlap with delocalised ring
21
Q
Where do electron donating groups promote substitution?
A
.They increase the electron density at positions 2, 4, and 6.So electrophiles are more likely to react at these positions.The group directs substitution to positions 2, 4, and 6.2, 4-directing.The weaker position at 3 and 5 are rarely substituted
22
Q
What are electron withdrawing substitition groups also known as, why?
A
.Side chains that decrease electron density slow electrophile reactions compared to benzene, so are ‘deactivating’ groups
23
Q
Give an example of an electron withdrawing substitution group
A
.NO2 – O is more electronegative, drawing electrons away from the delocalised ring
24
Q
Where do electron withdrawing groups promote substitution?
A
.It withdraws electron density at position 2, 4, and 6 – meaning that electrophiles are unlikely to react at these positions.The group directs substitutes to position 3.3- directing.The weaker positions at 2 and 4 are rarely substituted
25
Where does NH2 direct?
2, 4
26
Where does OH direct?
2, 4
27
Where does OR direct?
2, 4
28
Where does F, CL, Br, and I direct?
2, 4
29
Where does R direct?
2, 4
30
Where does NO2 direct?
3
31
Where does COOH direct?
3
32
Where does CHO direct?
3
33
Where does COOR direct?
3
34
What is R?
An alkyl group
35
In a carbonyl group, what are the charges on the atoms?
The carbon is delta +The oxygen is delta –
36
What is a carbonyl group?
C double bonded to O
37
What are aldehydes?
C=O group at the end of the carbon chain
38
How are aldehydes named?
start from the aldehyde end, suffix ‘-al’
39
What are ketones?
C=O group somewhere along the carbon chain, never at the end
40
How are ketones named?
C=O carbon should have lowest possible number
41
Primary alcohols will oxidise to what?
aldehydes and carboxylic acids
42
What is needed to oxidise primary alcohols? What will be seen?
An oxidising agent, acidified potassium dichromate K2Cr2O7/H+, needs heat, colour change if there is a reaction to green
43
Forming Aldehydes , how?
- Distillation- Only from primary alcohol- Product must be distilled off or it will oxidise further- Reaction mixture contains excess alcohol- Colour change from orange to green- Forms water
44
Forming Carboxylic Acids , how?
- Reflux- From primary alcohol- Heated under reflux with excess of [O] – ensures reaction goes to completion- Colour change from orange to green- Doesn’t form water (unless from primary alcohol, but not if from aldehyde)
45
What is benzene called when it has a ketone group attached to carbon 1?
Phenyl ethanone
46
What is benzene called when it has an aldehyde group attached to carbon 1?
Phenyl methanal
47
Secondary alcohols will oxidise to what?
Ketones
48
Conditions for oxidation of secondary alcohols
an oxidising agent, acidified potassium dichromate- Heated under reflux with excess of [O], ensures reaction goes to completion- Colour change from orange to green
49
What do tertiary alcohols oxidise to?
Tertiary alcohols don’t oxidise at all
50
Draw the product of the oxidation of propan-2-ol
check notes
51
Conditions for reduction of aldehydes and ketones?
Reduction – - Needs a reducing agent, NaBH4/H2O (sodium tetrahydridoborate)- Contains BH4- ions which is a source of H- ions• Need to warm it using water or ethanol as a solvent
52
What is a H- ion called?
A hydride ion
53
• Aldehydes and ketones can be reduced to their respective alcohols using what?
the reducing agent NaBH4
54
If reduced CH3CH2CHO, you would get what?
CH3CH2CH2OH
55
Reducing an aldehyde creates a what?
primary alcohol
56
Reducing a ketone creates a what?
Secondary alcohol
57
NaBH4 produces the nucleophile what?
H-hydride ion
58
Draw the equation for the reduction of CH3CH2CHO
check notes
59
Draw the equation for the reduction of CH3CH2COCH2CH3
Check notes
60
Draw the mechanism for the reduction of CH3CH2CHO
check notes
61
Hydrogen cyanide can be added across the C=O bond of which two functional groups?
aldehydes and ketones
62
What is hydrogen cyanide?
HCNa colourless and extremely poisonous liquid that cannot be safely used in labs
63
How is HCN used in labs? Why?
- We use sodium cyanide and sulphuric acid to provide the hydrogen cyanide in the reactions- This makes it safer to carry out in a lab but it is still very dangerous
64
Why is the reaction of carbonyl compounds with HCN useful?
The reaction is very useful as it is a way of increasing the length of the carbon chain
65
How to name hydroxy nitriles
- Need to include the carbon on the CN as part of the longest carbon chain'nitrile' is the suffix
66
Draw the mechanism of the reduction of CH3CH2CH2CH2CHO
Check notes
67
Draw the mechanism of the reduction of CH3COCH3
check notes
68
Draw the equation for the reaction of CH3CH2CHO and HCN
Check notes
69
Draw the mechanism of the reaction of CH3CH2CHO and HCN
Check notes
70
Draw 2-hydroxybutanenitrile
check notes
71
What does tollens agent react with?
- Tollens’ reagent oxidises aldehydes to carboxylic acids but does not oxidise ketones
72
How to form tollens agent
- Tollens reagent = NaOH(aq) added to AgNO3 until a brown precipitate is formed, then add dilute NH3 until precipitate dissolves to form a colourless solution
73
What does a positive tollens agent test form
A silver mirror
74
WHat happens to silver ions in tollens test
- Silver ions are reduced:o Ag+(aq) + e- Ag(s¬)
75
Draw the general formula for tollens test
cHECK NOTES
76
WHat is used to test for carbonyl compounds?
2-4, dinitrophenylhydrazine (2, 4-DNP or brady’s reagent)
77
In the carbonyl compound test, how is brady's agent used?
Is dissolved in methanol and sulfuric acid
78
What colour does brady's agent turn?
- Reacts with carbonyl groups to form a bright orange precipitate
79
WHat does brady's agent react with?
- It only happens for compounds with a C=O bond, so aldehydes and ketones- Doesn’t work for COOH or esters
80
WHat is the orange precipitate from Bradys agent?
- The orange precipitate is derivative of a carbonyl compound and can be used to identify an unknown compound with a carbonyl group
81
The method for identifying a carbonyl compound using bradys agent
1. You are given an unknown compound with a carbonyl group2. Add 2,4-DNP to see an orange precipitate formed that is a derivative of the carbonyl group3. Filter off the crystals using a Buchner funnel and water pumpThis is an impure solid you need to have a pure solid, so we need to purify and then recrystallize4. Dissolve the crystals in the smallest amount of hot solvent (ethanol) to purify and then put the test-tube in ice water to allow the pure solid to recrystallize5. Filter off the crystals again using a Buchner funnel and water pump, this time you have a pure solid6. Find the melting point of the pure solid7. Compare to a known database of melting points for carbonyl derivatives to identify carbonyl
82
Descibr carboxylic acids
- A homologous series which contain the carboxyl functional group COOH- The bonds are in a planar arrangement- Include a carbonyl (C=O) group and a hydroxyl (O-H) group
83
How to name carboxylic acids
- Select the longest chain of C atoms containing the COOH group- Remove the e and add oic acid after the basic name- Number the chain starting from the end nearer the COOH group- As in alkanes, prefix with alkyl substituents- Side chain positions are based on the C in COOH being 1
84
Why are carboxylic acids soluble in water?
Carboxylic acids are polar molecules, electrons are drawn towards the oxygen atoms.Hydrogen bonds form between the highly polarised hydrogen and oxygen atoms on the molecules.This makes them soluble in water.
85
As the carbon chain gets longer, carboxylic acids get less soluble, why?
this happens as the non-polar carbon chain having a greater effect on the overall polarity.
86
Acid + Metal -->
Salt and hydrogen
87
Acid + Metal Oxide -->
Salt and water
88
Acid + Alkali -->
salt and water
89
Acid + Metal Carbonate -->
Salt and water and carbon dioxide
90
2HCl(aq) + 2Na(aq) -->
2NaCl(aq) + H2(g)
91
2HCl(aq) + Na2O(s) -->
2NaCl(aq) + H2O(l)
92
HCl(aq) + NaOH(aq) -->
NaCl(aq) + H2O(l)
93
2HCl(aq) + Na2CO3(s) -->
2NaCl(aq) + H2O(l) + CO2(g)
94
Carboxylic acids are ___ acids and take place in ____ reactions with metals and _______ reactions with bases (alkali’s, metal oxides and metal carbonates).
weak redox neutralisation
95
In some reactions of carboxylic acids what is formed?
carboxylate salts
96
What is a carboxylate salt?
One of the ions formed in the salt is a carboxylate ion.
97
CH3COOH
CH3COO- + H+
98
Ethanoic acid
Ethanoate ion + Hydrogen ion
99
Name and give the structure of the 3 first carboxylate ions
- Methanoate ion CHOO-- Ethanoate ion CH3COO-- Propanoate ion CH3CH¬2COO-
100
Benzene with a carboxylic acid group when ionised becomes what?
a Benzoate ion NOT a benzanoate ion
101
, Ethanoic acid + Sodium -->
Sodium ethanoate + Hydrogen
102
Ethanoic acid + sodium
sodium ethanoate + hydrogen
103
Ethanol + sodium
sodium ethoxide + hydrogen
104
Sodium ethanoate written structure
Na+CH3COO-
105
Sodium ethoxide writtren structure
C2H5O-Na+
106
A derivative of carboxylic acid is what?
a compound that can be hydrolysed to form the parent carboxylic acid it was formed form.
107
All carboxylic acid derivatives have a common sequence of atoms in their structure known as what?
an acyl group.
108
Draw an acyl group
CHECK NOTES OR GOOGLE
109
Draw an ester group
CHECK NOTES OR GOOGLE
110
Draw an acyl chloride group
CHECK NOTES OR GOOGLE
111
Draw an amide group
CHECK NOTES OR GOOGLE
112
Draw an acid anhydride group
CHECK NOTES OR GOOGLE
113
Draw Ethanoic acid + methanol
CHeck NOTES OR GOOGLE
114
What is esterfication?
This is a reaction where an alcohol and a carboxylic acid react together to form an ester and water. It is a condensation reaction.
115
Reagents and conditions for esterfication?
Reagents: catalyst (concentration H2SO4)Conditions: warm
116
Propanoic acid + ethanol
ethyl propanoate + water
117
What is special about esters?
Most esters have a pleasant odour.Depending on the alcohol and acid used, many different fragrances can be made.
118
What is an acid anhydride?
An acid anhydride is formed when water is removed from two molecules of carboxylic acid.
119
2 ethanoic acids form what when water is removed?
ethanoic anhydride
120
How can you make an ester using an alcohol?
You can form an ester using acid anhydride and an alcohol.
121
Acid anhydride + alcohol
ester + carboxylic acid
122
Ethanoic anhydride + methanol
methyl ethanoate + ethanoic acid
123
Draw ethanoic anhydride + methanol
check notes
124
What is hydrolysis?
Hydrolysis is the chemical breakdown of a compound in the presence of water or in aqueous solution
125
What are the two types of hydrolysis?
There are two types:1. Acid hydrolysis2. Alkaline hydrolysis
126
Describe the process of acid hydrolysis
- Heated under reflux with dilute aqueous acid- Ester broken down by water using the acid as a catalyst- Reversible reaction
127
Finish the equationCH3COOCH3 + H2O HCl
CH3COOH + HOCH3
128
Describe the process of alkaline hydrolysis
- Reflux with aqueous alkali (NaOH or KOH)- Get a carboxylate salt and alcohol- Salt can be used to make soap – saponification- Irreversible
129
Finish the equationCH3COOCH3 + NaOH
CH3COONa + HOCH3
130
Draw an acyl group
check notes or google
131
Draw an acyl chloride
check notes or google
132
How to name an acyl chloride group
The primary suffix name is based on the longest carbon chain name (minus ‘e’) + ‘oyl chloride’ for the COClThe carbon atoms are numbered from the C with the acyl functional group
133
Draw propanoyl chloride
check notes or google
134
Draw benzoyl chloride
check notes or google
135
Amines can be classified as primary, secondary, and tertiary, how is this determined?
This is determined by the number of carbon alkyl (carbon chain) or aryl (benzene ring) attached to the N atom.
136
Draw a primary amine
check notes or google
137
Draw a secondary amine
check notes or google
138
Draw a tertiary amine
check notes or google
139
How to name amines
If the amine (NH2) group is on the end of the carbon chain, the suffix is amine. You add the suffix to the alkyl group.If the amine (NH2) group is on any other carbon chain except carbon 1, the prefix is amino. You need to give the position of the amine group.In secondary and tertiary amines that contain the same alkyl group you have a prefix di or tri.
140
In secondary and tertiary amines that contain two or more different alkyl groupsThe compound is named as an what?
N-substituted derivative
141
Draw N-methl propylamine
check notes
142
Draw N-ethyl N-methyl propylamine
check notes
143
Amides can be classified as primary, secondary, or tertiary, how is this determined?
This is determined by the number of carbon atoms attached to the N atom
144
Draw a primary, tertiary and secondary aminde (using R)
check notes
145
Formula of propanamide
CH3CH2CONH2
146
Formula of benzamide
C6H5CONH2
147
Formula of N-ethyl butanamide
CH3CH2CH2CONHCH2CH3
148
Formula of N, N-dimethyl methanamide
CHON(CH3)CH3
149
How are acyl chlorides made?
by reacting a carboxylic acid with thionyl chloride (SOCl2)
150
CH3CH2COOH + SOCl2
CH3CH2COCl + SO2 + HCl
151
What would you see if HCl is produced as a product in carbonyl reactions?
Steamy white fumes
152
Describe the reaction of acyl chloride and alcohols
With Alcohols to Form EstersThis is a vigorous reaction which happens at room temperature.
153
Propanoyl chloride + propan-1-ol
propyl propanoate + HCl
154
Describe the reaction of acyl chloride and phenol
With phenol to form an aromatic esterEsters are formed again during the esterification reaction between phenol and an acyl chloridePhenol + acyl chloride ester + HCl
155
Phenol + propanoyl chloride
phenyl propanoate + hydrogen chloride
156
Describe the reaction of acyl chloride and water
With water to form carboxylic acidThis is a vigorous reaction with cold water
157
Propanoyl chloride + water
propanoic acid + hydrogen chloride
158
Describe the reaction of acyl chloride and ammonia
With ammonia to form amidesThis is a violent reaction at room temperature to form a primary amide
159
Propanoyl chloride + ammonia
propenamide + ammonium chloride
160
Describe the reaction of acyl chloride and amines
With amines to form amidesThis is a violent reaction at room temperature to form secondary amides
161
Propanoyl chloride + methylamine
N-methylpropanamide + methylammonium chloride
162
Ester 1 ( C6H5COHCOOC(CH3)2 ) is less soluble than mandelic acid ( C6H5CH(OH)COOH ), why?
Hydrogen bonds are formed with water, between oxygen and hydrogen, mandelic acid has 2 OH groups (whilst ester 1 has 1), therefore more hydrogen bonds can be formed and so it is more soluble
163
Define acid
Acid – In water, an acid releases hydrogen ions (H+) into solution
164
Define base
Base – A base is a compound that neutralizes an acid, by accepting a hydrogen ion, to form a salt
165
Define salt
Salt – A salt is the product of a reaction in which the H+ ions from the acid are replaced by the metal or ammonium ions
166
HCl + OH-
H2O + Cl-
167
Bases donates _ electrons to the hydrogen ion to form a ___ ___ bond, bases can either have a ___ ___ or a ____ ___.
2 dative covalentlone pairnegative charge
168
How is ammonia a base?
Ammonia (NH3) is a base, it accepts a proton to become an ammonium ion.
169
NH3 + HCl
NH4Cl
170
Amines behave as ___ in chemical reactions
bases
171
How do amines behave as bases in chemical reactions?
The lone pair of electrons on the nitrogen accepts a proton (a hydrogen ion)A dative covalent bond is formed, they form an ammonium ion
172
Ethylamine + H+
Ethylammonium ion
173
CH3CH2NH2 + H+
CH3CH2NH3+
174
Ethylamine + HCl
Ethylammonium chloride
175
CH3CH2NH2 + HCl
CH3CH2NH3Cl
176
The strength of a base depends on how available the nitrogen’s lone pairs of electrons is, how?
A lone pair of electrons are more available if its electron density is higherThe higher density, the more available the lone pair, the stronger the base
177
How strong of a base are aromatic amines? Why?
For aromatic amines, the benzene ring pulls the electrons towards the delocalized ring, electron density increases, weak base
178
How strong of a base is ammonia? Why?
For ammonia, it doesn’t have an aromatic group to pull the lone pair away or an alkyl group to push the lone pair of electrons forward, base
179
How strong of a base are aliphatic amines? Why?
For aliphatic amines (RNH2), the alkyl group pushes the electrons forward, towards the nitrogen, so the electron density increases, and the lone pair is more available, strong base
180
How to form primary aliphatic amines?
1. Ammonia has a lone pair of electrons on the N atom which allows it to act as a nucleophile in a reaction with a haloalkane, the product of this reaction is an ammonium salt2. Aqeous alkali (NaOH) is added to generate the amine from the salt
181
Conditions for formation of primary aliphatic amines
For this reaction to happen, the conditions needed are:- Excess NH3- Ethanol as a solvent to prevent substitution of the haloalkane by water to make an alcohol – also called ethanolic ammonia
182
What are the equations for the formation of ethylamine, using 1-chloroethane?
CH3CH2Cl + NH3 CH3CH2NH3+Cl-1-chloroethane + ammonia ethylammonium chloride CH3CH2NH3+Cl- + NaOH CH3CH2NH2 + NaCl + H2OEthylammonium chloride + sodium hydroxide ethylamine + sodium chloride + water
183
How are secondary aliphatic amines formed?
The primary amine can react with the haloalkane to make a secondary amine.
184
What are the equations for the formation of di-ethyl amine, using 1-chloroethane and ethylamine?
This is a two stage reaction:1. CH3CH2NH2 + CH3CH2Cl (CH3CH2)2NH2+Cl-Ethyl amine + 1-chloroethane Di-ethyl ammoniumchloride2. (CH3CH2)2NH2+Cl- + NaOH (CH3CH2)2NH + NaCl + H2ODi-ethyl ammoniumchloride + sodium hydroxide Di-ethyl amine + sodium chloride + water
185
The secondary amine can react with the haloalkane to make a tertiary amine, what is the two step reaction for this? Using 1. (CH3CH2)2NH + CH3CH2Cl
1. (CH3CH2)2NH + CH3CH2Cl (CH3CH2)3NH+Cl-Secondary amine + haloalkane salt (triethyl ammonium chloride)2. (CH3CH2)3NH+Cl- + NaOH (CH3CH2)3N + H2O + NaClSalt + sodium hydroxide tertiary amine + water + sodium chloride
186
Draw the mechanism for CH3Cl + CH3CH2NH2
CHECK NOTES
187
Phenylamine is made by the reduction of _____
nitrobenzene
188
C6H5NO2 _____ C6H5NH2
reduction with concentrated HCl and Sn in reflux
189
What is the two step reaction for the formation of phenylamine from nitrobenzene?
1. C6H5NO2 + 7[H] C6H5NH3+Cl- + 2H2ONitrobenzene + reducing agent phenyl ammonium chloride (a salt) + water2. C6H5NH3+Cl- + NaOH C6H5NH2 + NaCl + H2Ophenyl ammonium chloride (a salt) + sodium hydroxide phenylamine + sodium chloride + water
190
C6H5NO2 + 6[H]
C6H5NH2 + 2H2O
191
What are aminos?
Amino are organic compounds containing amine and carboxylic acid functional groups, the side R chain is specific to each amino acid
192
Draw the general displayed formula for an amino acid
check notes
193
What is the general written formula for amino acids?
RCH(NH2)COOH
194
What are the three types of amino acids and how do they differ?
- Alpha-amino acidso 2 carbons- Beta-amino acido 3 carbons- Gamma-amino acidso 4 carbons
195
Write the formula for glycine and state its proper name
o HCH(NH2)COOHo Proper name is 2-amino ethanoic acid
196
Write the formula for alanine and state its proper name
o H3CH(NH2)COOHo Proper name is 2-amino propanoic acid
197
Write the formula for phenylalanine and state its proper name
o H5C6H2CCH(NH2)COOHo 2-amino, 3-phenyl propanoic acid
198
How is an amino acid both a proton donor and acceptor?
Amino acids contain an acid group (COOH) and a base group (NH2)The COOH is a proton donor, and the NH2 is a proton acceptor
199
As amion acids are both proton donors and acceptors, what can they do?
This means it can react with itself so the H+ ion from the COOH is donated to the NH2, this forms an ion called a zwitterion
200
What is the charge on a zwitterion?
0
201
Zwitterions only form at their specific isoelectric point, what is an isoelectric point?
pH at which an amino acid exists as a zwitterion
202
What is the isoelectric point affected by?
Different R groups
203
Draw the general formula for the formation of zwitterions
check notes
204
Alanine’s isoelectric point is ?
pH 6.01
205
Draw the formation of alanine's zwitterion
check notes
206
What happens to zwitterions in acidic conditions?
a lower pH, it is in acidic conditions, and so H+ ions are added wherever they can be
207
What happens to zwitterions in basic conditions?
At pH 7.01, a higher pH, it is in alkaline conditions, and so H+ ions are removed wherever they can be
208
Draw the product of an alanine zwitterion in acidic conditions
check notes
209
Draw the product of an alanine zwitterion in basic conditions
check notes
210
What is glutamic acid's isoelectric point?
3.22 pH
211
Draw the product of an glutamic acids zwitterion in basic conditions
Check notes
212
Draw the product of an glutamic acids zwitterion in acidic conditions
Check notes
213
What is lysine's isoelectric point?
9.59pH
214
Draw the product of an lysine's zwitterion in acidic conditions
Check notes
215
Draw the product of an lysineds zwitterion in basic conditions
check notes
216
What's the equation for alanine (R=CH3) and HCL?
H3CCH(NH2)COOH + HCl CH3CH(N+H3)COOH Cl-
217
What's the equation for alanine (R=CH3) and NaOH?
CH3CH(NH2)COOH + NaOH CH3CH(NH2)COO-Na+ + H2O
218
What's the equation for alanine (R=CH3) and methanol?
CH3CH(NH2)COOH + CH3OH CH3CH(NH2)COOCH3 + H2O
219
WHat are stereoisomers?
Stereoisomers are species with the same structure but a different arrangement of atoms in space
220
WHich one of E-but-2-ene, and Z-but-2-ene is trans?
E-but-2-ene
221
What is superimpose?
to place or lie over another and they are the same
222
What does it mean if you can or cannot superimpose two molecules of the same structure?
If you can superimpose, they are identical, and cannot form an optical isomerIf you cannot superimpose, they are not identical, and can form an optical isomer
223
When you have 4 different groups attached to a carbon, the molecule shows what?
optical isomerism
224
WHat are chiral centres?
Carbon atoms with 4 different groups attached are called chiral centers
225
Where does the word chiral come from?
Chiral is the Greek word for hands
226
Draw 2-bromobutane and identify the chiral centre
check notes
227
Draw 2, 3-dimethyl pentane and identify the chiral centre
check notes
228
Draw chloroethanoic acid and identify the chiral centre
check notes (there is no chiral centre)
229
How to draw optical isomerism?
- Put chiral carbon in middle and draw groups off of it - Use wedges, dashes, and lines as usual- Draw it like a tetrahedron- Mirror it
230
For a substance that can undergo optical isomerism, the different optical isomers are called what?
enantiomers
231
What is a racemic mixture?
A racemic mixture is when you have a mixture of a substances enantiomers together.
232
Draw the optical isomerism of CH3 C (OH) Cl
check notes
233
If a molecule has 1 chiral center, there will be _ isomers.
2
234
If a molecule has 2 chiral centers, there will be _ isomers.
4
235
For every chiral center, there are ___ possible isomers.
two
236
Draw the isomers of CH3 C (Cl) C (OH) Br
CHECK NOTES
237
Explain how a time of flight spectrometer works
1. injection2. vaporization3. ionisation chamber4. acceleration area5. drift region6. detector
238
Describe and explain fragments in mass spectrometry
- Excess energy from the ionization process can be transferred to the molecular ion and cause it to split (fragment)- When it fragments:o It produces a smaller positive ion and radicalo The smaller positive ion is detectedo Fragment ions can be broken down further still
239
What does a CH bond do when it absorbs IR?
stretches
240
What does a HCH bond do when it absorbs IR?
bends
241
Each bond in IR spectroscopy vibrates with a unique freuquency, which is picked up by what?
the spectrometer
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What does vibration in IR spectroscopy depend on?
- Bond strength- Bond length- Mass of the bonded atom
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What are the types of movement found in IR spectroscopy?
- Symmetrical stretching- Antisymmetrical stretching- Scissoring- Rocking- Wagging- Twisting
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How to identify alcohols with IR spectorscopy?
Primary alcohol = 1050Secondary alcohol = 1100Tertiary alcohols = 1150OH bond = 3200-3640
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Mr of CH3+
15
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Mr of C2H5+
29
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Mr of C3H7+
43
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Mr of OH+
17
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Mr of C4H9+
57
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Equation of formation of C6H14+ in hexane mass spectrometry
C6H14 C6H14+ + e-
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Equation of formation of C4H9+ in hexane mass spectrometry
C6H14+ C4H9+ + •C2H5
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How to check for polarity on a molecule?
Ask the two questions:Are the surrounding atoms the same?Is there a long pair on the central atom?If the answer is yes to both its polar, if its no to both its polar, if its yes to one and no to the other its non-polar
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Rf =
distance of pigment / solvent front
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What does the Rf value tell you?
Generally if the Rf values are the same, they are the same substance (there are exceptions)
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Problems with Rf values
- Components can have similar Rf values- The unknown substance is new and there is no previous chemical to compare it with
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What is Thin Layer Chromatography (TLC)?
- TLC is very similar to paper chromatography- Rather than using chromatography/filter paper the stationary phase is a thin uniform layer (usually silica gel) coated on a piece of plastic, metal, or glass- The mobile phase is a liquid which acts as a solvent for the substances you are trying to separate or analyze
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Steps of TLC
1. A base line is drawn in pencil across the plate and dots of the substances are placed along the line2. The plate is placed in a beaker of the solvent such that the level of the solvent is below the line and the solvent moves up the plate3. A lid is placed to ensure the atmosphere in the tank is saturated with the often volatile solvent which climbs up the plate causing the mixture to separate4. As the solvent front moves up the plate the mixture separates into its different components5. The solvent reaches near to the top of the plate and the plate is removed6. The solvent front is noted and the solvent is left to evaporate
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What happens if the substances are colorless in TLC?
- Using UV Lighto The stationary phase has a chemical added to it which will fluorescence under UV light, the spots need to be circled while under the light- Chemicallyo The chromatogram is dried and sprayed with a ninhydrin spray, amino acids react and turn a purple/brown colouro You can also use iodine crystals, the chromatogram is dried and placed in an enclosed container with a few iodine crystals, the iodine vapor in the container may either react with the pots on the chromatogram, or simply stick more to the spots than to the rest of the plate, either way the substances you are interested in may show up as brownish spots
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How does TLC work?
- Silica gel is a form of silicon dioxide (silica)- The silicon atoms are joined via oxygen atoms in a giant covalent structure- However, at the surface of the silica gel, the silicon atoms are attached to -OH groups- The surface of the silica gel is very polar and, because of the -OH groups, can form hydrogen bonds with suitable compounds around it as well as van der waals dispersion forces and dipole-dipole attractions- With a solid stationary phase, the pigments are adsorbed onto the surface of the solid particles or fibers- The relative forces of attraction between the stationary phase, the mobile phase, and the pigment mean that separation happens
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Define adsorption
Adsorption – is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface
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Which pigments will move how much in TLC?
- Insoluble pigmento Won’t move- Strong forces of adsorptiono More polar so won’t move a lot- Weak forces of adsorptiono Less polar so will move a lot
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When will the Rf value stay the same?
- Providing the temperature, stationery phase, and solvent stay the same, the Rf value will stay the same on repeats
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What is Gas liquid chromatography?
- In GLC a long column is often filled with a liquid compound- In thinner tubes, the stationary phase is coated to the inside surface of the tube- The sample is vaporized and pushed through the column by an inert carrier gas (most often nitrogen or helium)
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How does gas-liquid chromatography (GLC) work?
- Depending on the solubility of the different compounds in the stationary liquid phase, their boiling points and the temperature of the column, the different compounds will travel through the GLC column at different speeds- The length of time a compound remains in the column is known as the retention time- It is calculated from the time the sample is injected until the maximum peak heigh for that compound is observed on the display/chromatogram- Compare to a known database to find the molecule
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Explain how to find the proportion of components in GLC?
The area under the peaks can be used to calculate the composition of the mixtureArea of triangle = ½ x base x heightWork out individual areas and add them togetherWork out percentage of area taken up by each peak
