Organic Chemistry III - Topic 18 Flashcards
(152 cards)
1
Q
what are aliphatic chemicals
A
straight or branched chain organic substances
2
Q
what are aromatic or arene chemicals
A
substances with one or more ring of six carbon atoms with delocalised bonding.
3
Q
What is the molecular formula of Benzene
A
C₆H₆
4
Q
What is the basic structure of Benzene?
A
- six carbon atoms in a hexagonal ring, with one hydrogen atom bonded to each carbon atom.
- Each carbon atom is bonded to two other carbon atoms and one hydrogen atom by single covalent σ-bonds. This leaves one unused electron in a p orbital on each carbon atom.
- so the six p electrons are delocalised in a ring structure above and below the plane of carbon atoms.
5
Q
What structure did Kekulé propose for Benzene in 1865?
A
Kekulé suggested that Benzene consisted of alternate single and double covalent bonds between carbon atoms.
6
Q
How is delocalisation represented in Benzene?
A
circle is drawn in the formula to represent the delocalised system of electrons.
7
Q
Why is Kekulé’s proposed structure for Benzene incorrect?
A
- thermochemidal - based on the structure of cyclohexatriene (which has same structure as predicted benzene) the enlapy change of hydrogenation for benzene was predicted to be -360 kjmol-1, it was later discovered that benzene enthalpy change was actually -208 kjmol-1 meaning that the structre was more stable so was different to cyclohexatriene
- x ray diffraction - they show that all te bond lenghts between carbon atoms for benzene was the same which disproves predicted structre as double bonds are shorter
8
Q
What is the bond angle in Benzene?
A
The H-C-C bond angle in Benzene is 120°.
9
Q
What makes Benzene more thermodynamically stable?
A
The delocalisation of the six p electrons over the whole ring, making the molecule more stable than a structure with separate double bonds.
10
Q
Why does Benzene not undergo addition reactions?
A
Addition reactions would disrupt the delocalised electron system, which is stable. Therefore, Benzene usually undergoes substitution reactions instead.
11
Q
why does benzene undergo electrophilic substitutions
A
because it has a high electron density that attracts electrophiles.
12
Q
what is the delocalisation energy
A
The increase in stability connected to delocalisation
13
Q
disadvantages of benzene
A
Benzene is a carcinogen
14
Q
benefits of methylbenzene
A
- Methylbenzene is less toxic
- reacts more readily than benzene as the methyl side group releases electrons into the delocalised system making it more attractive to electrophiles.
15
Q
what will benzene produce in the combustion of benzene
A
Benzene will combust with a very sooty flame
16
Q
halogenation of benzene
change in functional group
conditions and mechanism
A
Change in functional group: benzene —> bromobenzene Reagents: Bromine
Conditions: Iron(III) bromide catalyst FeBr3 or ACl3
Mechanism: Electrophilic substitution
17
Q
how is the electrophile Br+ or Cl+ generated for the bromination or chlorination of benzene (for halogenation reaction)
A
AlCl3 + Cl2 —> AlCl4– + Cl+
FeBr3 + Br2 —> FeBr4– + Br+
18
Q
draw mechanism for chlorination of benzene
A
pg 3 chemrevise
19
Q
write overall equation for bromination of benzene
A
pg 3 chemrevise
20
Q
draw abbreviated and displayed formula of benzene
A
pg 1 chemrevise
21
Q
nitration of benzene change in functional group, reagent, mechanism, conditions and electrophile
A
Change in functional group: benzene —-> nitrobenzene Reagents: conc nitric acid in the presence of concentrated sulfuric acid (catalyst)
Mechanism: Electrophilic Substitution
conditions: temp 60 degrees
Electrophile: NO2+
22
Q
equation for the formation of NO₂⁺
A
HNO₃ + 2H₂SO₄ → NO₂⁺ + 2HSO₄⁻ + H₃O⁺
23
Q
overall equation for nitration of benzene
A
pg 3 chemrevise
24
Q
mechanism for the nitration of benzene
A
pg 3 chemrevise
25
why is the nitration of benzene done at 60 degrees
as if you use a higher temp a second nitro group would be substituted onto different positions on the ring
26
What is the importance of nitration of benzene?
Used in synthesis of explosives (e.g. TNT) and formation of amines for dyes.
27
hydrogenation of benzene reaction, reagent, conditions and type of reaction
Reaction: benzene ---> cyclohexane
Reagents: Hydrogen
Conditions: Nickel catalyst at 200C and 30 atm Type of reaction: Addition and reduction
28
write the overall equation for the hydrogenation of benzene
pg 4 chemrevise
29
(friedal craft) alkylation of benzene change in functional group, reagents, conditions, mechanism
Change in functional group: benzene ---> alkylbenzene Reagents: chloroalkane in the presence of anhydrous aluminium chloride catalyst
Conditions: heat under reflux
Mechanism: Electrophilic Substitution
30
how is the CH3CH2+ + AlCl4- generated in alkylation of benzene
CH₃CH₂Cl + AlCl₃ → CH₃CH₂⁺ + AlCl₄⁻
31
write the overall equation for the alkylation of benzene and draw the mechanism
pg 4 chemrevise
32
acylation of benzene change in functional group, reagents, conditions and mechanism
Change in functional group: benzene ---> phenyl ketone Reagents: acyl chloride in the presence of anhydrous aluminium chloride catalyst
Conditions: heat under reflux (50OC)
Mechanism: Electrophilic substitution
33
equation for the formation of the acylium ion electrophile in the acylation of benzene
CH₃COCl + AlCl₃ → CH₃CO⁺ + AlCl₄⁻
34
What is the overall reaction and mechanism for benzene and ethanoyl chloride?
pg 5 chemrevise
35
Name some electron-releasing side groups.
Alkyl groups, phenol (-OH), and amine (-NH₂)
36
How do electron-releasing side groups affect benzene’s reactivity?
They increase electron density in the ring, making it more attracted to electrophiles under milder conditions.
37
What happens OH or Cl or NH₂ are attached to benzene?
Their lone pairs become delocalised with the benzene ring, affecting their chemical properties.
38
How does delocalisation affect phenol’s acidity?
Delocalisation makes the C-O bond stronger and the O-H bond weaker. Phenol does not act like an alcohol- it is more acidic and does not oxidise
39
How does delocalisation affect chlorobenzene
- The C-Cl bond is made stronger so typical halogenoalkane substitution and elimination reactions do not occur
- the electron rich benzene ring will repel nucleophiles
40
How does delocalisation affect phenylamine
it makes less basic as lone pair is delocalised and less available for accepting a proton
41
draw structure of phenol
chemrevise page 6
42
describe structure of phenol
- In a phenol the OH group is directly attached to the benzene ring.
43
What happens to the lone pair on oxygen in phenol?
It becomes delocalised into the benzene ring’s π-electron system.
44
How does delocalisation of the –OH group in phenol affect reactivity?
It increases electron density in the ring and alters the reactivity of both the –OH group and the ring.
45
How does phenol’s acidity compare to carboxylic acids?
Phenols are weaker acids than carboxylic acids
46
Which bases do phenols react with?
Phenols react with sodium metal and sodium hydroxide, but not sodium carbonate. as phenol is not a strong enough acid to react
47
Why does solid phenol dissolve when NaOH is added?
Because it forms sodium phenoxide, which is soluble.
48
write equation for phenol with sodium and sodium hydroxide
pg 6 chemrevise
49
What are the reagents and conditions for phenol’s reaction with bromine?
Reagents: Bromine water
Conditions: Room temperature
50
write equation for phenol with bromine
pg 6 chemrevise
51
Why is phenol more reactive with bromine than benzene
- Because the oxygen’s lone pair is partially delocalised into the ring so it increases electron density in the ring, polarising Br₂.
- does not need a FeBr3 catalyst like benzene
- undergoes multiple substitution whereas benzene will only add one Br
52
What are some uses of phenol
In production of plastics, antiseptics, disinfectants, and resins for paints.
53
What is meant by delocalisation in the benzene ring?
It’s the sharing of electrons across all six carbon atoms in benzene, forming a stable π-electron system above and below the ring.
54
How are secondary amines and amides named when two different alkyl groups are present?
Use N- to show the smaller group is attached to the nitrogen (e.g. N-methylpropan-1-amine).
55
What if both alkyl groups in a secondary amine are the same length in amides, how would you name it?
The common name does not use N- (e.g. diethylamine)
however IUPAC name still uses N- (e.g. N-ethylethanamine).
56
Name CH₃CH₂CH₂NHCH₃
N-methylpropylamine
57
How are tertiary amines named?
Use N,N- to show two groups are attached to the nitrogen.
58
Name CH₃CH₂CH₂N(CH₃)₂
N,N-dimethylpropylamine
59
How are molecules with two amine groups named?
Use diamino as a prefix.
60
Name this structure: H₂N–(CH₂)₆–NH₂
1,6-diaminohexane
61
What prefix is used if there’s a higher priority group (e.g. –COOH) along with an amine?
amino
62
What is a characteristic physical property of amines?
Amines have a fishy smell
63
Why can small amines dissolve readily in water?
They can form hydrogen bonds with water. (nitrogen and hydrogen form H bond)
64
How do primary aliphatic amines act as Bronsted-Lowry bases?
as the lone pair on nitrogen forms a dative bond H⁺ and so accepts a proton
65
Are primary aliphatic amines stronger or weaker bases than ammonia? Why?
Stronger, because alkyl groups are electron-releasing and push electrons towards the nitrogen atom, increasing electron density on nitrogen and so make it a stronger base.
66
Why are secondary amines stronger bases than primary amines?
They have more alkyl groups, increasing the inductive effect, and pushing more electron density onto nitrogen.
67
Why aren’t tertiary amines the strongest bases despite having more alkyl groups?
They are less soluble in water, making them less effective as bases in aqueous solutions
68
why does Primary aromatic amines such as phenylamine not form basic solution
The lone pair on nitrogen delocalises into the benzene ring, making it less available to accept a proton.
69
what do amines form when reacting with acids and give me the example reaction of methylamine with hydrochloric acid?
- they form ammonium salts
- CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻ (methylammonium chloride)
70
how to convert an ammonium salt back to an amine
- addition of NaOH
71
Reaction of methylamine with sulfuric acid?
2CH₃NH₂ + H₂SO₄ → (CH₃NH₃⁺)₂SO₄²⁻
72
How can you make a basic buffer using amines and give 3 examples?
Combine a weak base with its ammonium salt
- Ammonia and ammonium chloride
- Methylamine and methylammonium chloride
- Ethylamine and ethylammonium chloride
73
What is formed when water is evapourated from ionic salts (e.g ammonium salt)
They form solid crystals due to the strong ionic interactions between the ions.
74
How do ionic salts affect the solubility of compounds in acids
Ionic salts increase the number of ions in solution, which increases electrostatic shielding. This reduces the electrostatic attraction between oppositely charged ions, preventing ion pair formation and helping the compound stay dissolved in its ionised, more soluble form.
75
How do primary amines react with halogenoalkanes?
Primary amines react with halogenoalkanes via nucleophilic substitution, forming a secondary amine.
76
draw the mechanism for the reaction and write the overall equation between ethylamine and bromoethane?
pg 9 chemrevise
77
What happens after a secondary amine forms during the reaction with halogenoalkanes
The secondary amine can react with more halogenoalkane to form a tertiary amine, which can further react to form a quaternary ammonium salt.
78
Reaction with primary amines with acyl chlorides Change in functional group, Reagent, Conditions
Change in functional group: acyl chloride ---> secondary amide
Reagent: primary amine
Conditions: room temp.
79
What is an example of a product made from the reaction of an aromatic amine with an acyl chloride and draw reaction?
Paracetamol is made by the reaction of an aromatic amine with an acyl chloride, resulting in the formation of an amide.
80
How can primary amines be formed in a one-step reaction?
Primary amines can be formed by nucleophilic substitution between halogenoalkanes and ammonia dissolved in ethanol
81
Why is the reaction between halogenoalkanes and ammonia not an ideal method for forming primary amines?
as the lone pair of electrons is still available on the N in the amine formed so the primary amine formed can react further, leading to secondary, tertiary amines, and quaternary ammonium salts, which requires separating the desired product.
82
How can the reaction between halogenoalkanes and ammonia be controlled to maximize primary amine production?
Using an excess of ammonia can limit further reactions and maximize the amount of primary amine formed.
83
draw the mechanism and write the full equation for the reaction between bromoethane and ammonia to form a primary amine
pg 10 chemrevise
84
Why is preparing amines from nitriles a better method than using halogenoalkanes and ammonia
it avoids the further substitution reactions that occur when halogenoalkanes react with ammonia.
85
what is the better method in forming primary amines
Step 1. convert halogenoalkane to nitrile by using KCN in aqueous ethanol (heat under reflux)
Step 2. reduce nitrile to amine by using LiAlH4 in ether or by reducing with H2 using a Ni catalyst.
86
What are the disadvantages of preparing amines from nitriles?
1) It is a two-step reaction, which may result in a low yield.
2) KCN (potassium cyanide) is toxic.
87
reduction of nitroarenes to aromatic amines reagent conditions and mechanism
Reagent: Sn and HCl or Fe and HCl Conditions: Heating
Mechanism: Reduction
88
What is the overall reaction for the reduction of nitrobenzene to phenylamine
pg 11 chemreise
89
formation of secondary amides using acyl chloride change in functional, reagent, conditions
Change in functional group:
acyl chloride ---> secondary amide
Reagent: primary amine Conditions: room temp
90
What are the two most common types of condensation polymers?
Polyesters and polyamides
91
What are the reactions involved in forming polyesters and polyamides
Diacyl dichloride + Diol → Poly(ester) + HCl
Diacyl dichloride + Diamine → Poly(amide) + HCl
Dicarboxylic acid + Diamine → Poly(amide) + Water
Dicarboxylic acid + Diol → Poly(ester) + Water
92
what is involved in condensation polymerization
two different monomers with the same functional group on both ends of the molecule react and a small molecule (such as H2O or HCl) is given off as a side-product.
93
Why is using carboxylic acid to make esters or amides less efficient than using acyl chlorides?
Carboxylic acids need an acid catalyst and give an equilibrium mixture, while acyl chlorides react to completion and don’t need a catalyst but release hazardous HCl fumes.
94
draw the common polyester terylene
pg 12 chemrevise
95
draw the common polyamides nylon 6,6 and kevlar
pg 12 chemrevise
96
how are polyesters and polyamides broken down
hydrolysis by acid an alkali
97
What intermolecular bonding is present in polyesters?
Polyesters have permanent dipole forces between the Cδ+=Oδ- groups in the different chains, in addition to London forces between the chains.
98
What intermolecular bonding is present in polyamides?
- hydrogen bonding between the lone pairs on oxygen in Cδ+=Oδ- groups and the H in the Nδ-—Hδ+ groups in the different chains.
- There are also permanent dipole-permanent dipole forces because the polar C=O bond and polar C-N bond
- London forces
99
Why do polyamides have higher melting points than polyesters?
because of stronger intermolecular forces, including hydrogen bonding, permanent dipole-permanent dipole forces, and larger London forces due to the presence of many electrons in the molecule.
100
what can the reactivity of condensation polymers be explained by
The reactivity can be explained by the presence of polar bonds which can attract attacking species such as nucleophiles and acids.
101
draw structure of amino acid
im not giving you the page number you should know this due to bio
102
What is the charge state of amino acids in their natural form?
Amino acids exist as dipolar zwitterions, with both a positive and a negative charge so has no overall charge
103
Why do amino acids have relatively high melting points?
due to the ionic interactions between zwitterions
104
What are the acidic and basic properties of amino acids?
The amine group is basic, and the carboxylic acid group is acidic.
105
draw amine species in alkaline solution, neutral solution and acidic solution
pg 14 chemrevise
106
How do amino acids act as buffers?
Amino acids act as weak buffers because they can resist changes in pH. When small amounts of acid or alkali are added, the pH changes gradually due to the presence of both acidic (–COOH) and basic (–NH₂) groups that can donate or accept protons.
107
What happens when amino acids react with acids or alkalis?
In acidic conditions, the amino acid gains an H+ ion e.g.
+NH₃-CH₂-CO₂⁻ + HCl → NH₃⁺-CH₂-CO₂H
In alkaline conditions, the amino acid loses an H+ ion e.g.
+NH₃-CH₂-CO₂⁻ + NaOH → NH₂-CH₂-CO₂⁻Na⁺ + H₂O
108
What happens to amino acids in high pH conditions?
the amino acid’s carboxyl group becomes deprotonated (COO⁻), and the amine group remains deprotonated.
109
how can you separate a mixture of amino acids
chromatography
110
method of chromatography of amino acid
1) take chromatography paper and draw a pencil line 1.5cm from bottom.
2) With a capillary tube put a small drop of amino acid on pencil line
3) Roll up paper and stand it in a large beaker.
4) The solvent in the beaker should be below the pencil line.
5) Allow to stand for 20 mins and mark final solvent level
6) Spray paper with ninhydrin and put in oven
111
how to calculate Rf value
Rf value = distance moved by amino acid/ distance moved by the solvent
112
how to identify amino acid after using chromatography
Compare an unknown amino acid’s Rf value with known values in a data book to identify the amino acid
113
Why is ninhydrin and an oven used in amino acid chromatography?
Amino acids are transparent, so spraying with ninhydrin and heating in an oven reveals red to blue spots.
114
Why are amino acids optically active?
Most amino acids are chiral with four different groups around the carbon; they rotate plane polarised light.
115
What type of bond holds the 3D corkscrew shape of a polypeptide chain
Hydrogen bonds between the H of the –NH group and the O of the C=O group.
116
Why is hydrogen bonding important in proteins?
It stabilises the secondary and tertiary structures by holding amino acid chains in specific 3D shapes like alpha-helices and beta-sheets.
117
What happens when proteins are heated with dilute acid or alkali?
They are hydrolysed into amino acids.
118
What functional groups in amino acids participate in esterification and acylation?
Both the carboxylic acid and amine group, and any amine/carboxylic groups in the R group
119
what is an esterfication reaction
a chemical reaction between a carboxylic acid and an alcohol to form an ester and water with the strong acid catalyst (concentrated sulfuric acid) and heat
120
What is a Grignard reagent?
A compound with the formula RMgX, formed by reacting a halogenoalkane with magnesium in dry ether.
121
How is a Grignard reagent prepared?
A halogenoalkane is dissolved in dry ether and reacted with magnesium
122
What is the role of a Grignard reagent in organic synthesis?
It is used to increase the carbon chain length in molecules.
123
What does a Grignard reagent form when reacted with methanal
a primary alcohol
example: CH₃CH₂MgI + HCHO → CH₃CH₂CH₂OH + Mg(OH)I
124
What is formed when a Grignard reagent reacts with other aldehydes?
A secondary alcohol
125
What is formed when a Grignard reagent reacts with a ketone?
A tertiary alcohol
example: CH₃CH₂MgI + CH₃COCH₃ → CH₃CH₂C(OH)(CH₃)₂ + Mg(OH)I
RMgI + R’COR” ---> RR’C(OH)R” + Mg(OH)I
126
What is formed when a Grignard reagent reacts with carbon dioxide?
A carboxylic acid
127
Besides Grignard reagents, how else can the carbon chain be increased?
By reacting halogenoalkanes with KCN to form nitriles or forming hydroxynitriles from carbonyls.
128
steps of recrystallisation
1. Dissolve the impure compound in a minimum volume of hot (near boiling) solvent.
2. filter hot solution through (fluted) filter paper quickly.
3. Cool the filtered solution by inserting beaker in ice
4. Suction filtrate with a buchner flask to separate out crystals
5. Wash the crystals with distilled water
6. Dry the crystals between absorbent paper
129
reason for Dissolving the impure compound in a minimum volume of hot (near boiling) solvent. (STEP 1) for recrystillisation
- An appropriate solvent is one which will dissolve both compound and impurities when hot and one in which the compound itself does not dissolve well when cold.
- the minimum volume is used to dissolve everything, obtain a saturated solution and to enable crystallisation on cooling
- If excess (solvent) is used, crystals might not form on cooling as compound will stay dissolved
130
why do we filter hot solution in recrystillisation
This step will remove any insoluble impurities and heat will prevent crystals reforming during filtration
131
why do we Cool the filtered solution by inserting beaker in ice
- cooling so crystals will reform but soluble impurities will remain in solution form as they are present in small quantities so the solution is not saturated with the impurities.
- Ice will increase the yield of crystals
132
why do we use Suction filtrate with a buchner flask to separate out crystals
The water pump connected to the Buchner flask reduces the pressure and speeds up the filtration.
133
why do we Wash the crystals with distilled water
To remove soluble impurities
134
why is their a low yield in recrystilisation
* Crystals lost when filtering or washing
* Some product stays in solution after recrystallisation
* other side reactions occurring
135
why would the yield be larger than 100% in recrystallisation
If the crystals are not dried properly the mass will be larger than expected which can lead to a percentage yield >100%
136
draw a Büchner funnel
page 21 chemrevise
137
how does steam distillation work
In steam distillation steam is passed into the mixture and the product vapour is distilled off with the water and condensed
138
advantages of steam distillation
The product distils at a lower temperature which can prevents decomposition of the product if it has a high boiling point
139
different hazards and how to prevent them
- Irritant - dilute acid and alkalis- wear googles
- Corrosive- stronger acids and alkalis wear goggles
Flammable – keep away from naked flames
- Toxic – wear gloves- avoid skin contact- wash hands after use
- Oxidising- Keep away from flammable / easily oxidised materials
140
what is a hazard
a substance or procedure that can has the potential to do harm.
141
what is a risk
the probability or chance that harm will result from the use of a hazardous substance or a procedure
142
What does a sharp melting point indicate about a sample’s purity?
it indicates the sample is very pure and matches the value in data books.
143
What does a lower and broader melting point range suggest?
The sample is impure, possibly containing solvents or other impurities.
144
how can melting point be measured
- in an electronic melting point machine
- by using a practical set up where the capillary tube is strapped to a thermometer immersed in some heating oil.
145
What type of oil is used in the melting point experiment?
An oil with a boiling point higher than the melting point of the sample and with low flammability.
146
draw apparatus for measuring melting point
page 21 chemrevise
147
What error can affect melting point measurements?
The thermometer may not reflect the actual sample temperature.
148
How is boiling point used to check purity of a liquid?
A pure liquid will boil at a constant temperature, while impurities may raise or lower the boiling point.
149
what can have an affect on the boiling point of a liquid
(atmospheric) pressure
150
Why is boiling point less reliable than melting point for identifying a substance?
Several substances may share the same boiling point.
151
have a go at the questions on pg 24 and pg 25 of chemrevise
152
know all organic and inorganic (pg 17 and 18)routes and tests (pg 26)
