Aromatic Compounds, Carbonyls and Carboxylic Acids + Nitrogen Chemistry Flashcards
1
Q
What can an aldehyde be oxidised into?
A
A carboxylic acid
2
Q
What is the equation for the oxidation of ethanal?
A
CH3CHO + [O] → CH3COOH, the reaction mixture is gently heated under reflux
3
Q
Where do carbonyl compounds have a dipole?
A
In the C=O functional group
4
Q
Which part of the C=O bond is attacked and what is it attacked by?
A
The delta positive carbon atom is attacked by a nucleophile that donates a pair of electrons to the electron deficient carbon
5
Q
What happens to the C=O bond when the nucleophile attacks the delta positive carbon?
A
The pi bond breaks and a reactive intermediate is formed, the electron pair is then donated to the neighbouring hydrogen to form an alcohol group and a stable product
6
Q
What reducing agent is commonly used in nucleophilic addition reactions?
A
NaBH4
7
Q
What is hydrogen cyanide and what is its chemical formula?
A
- A weak acid that partially ionises in solution, its chemical formula is HCN
- HCN + H2O ⇌ CN- + H3O+
- Other sources of CN- include NaCN
8
Q
Can the cyanide ion directly react with carbonyl compounds?
A
No, they can only react when the reaction is acidified as the polarity of the C=O bond is increased, which makes the carbonyl group more reactive
9
Q
What is the role of the acid in the nucleophilic addition reaction between butanal and hydrogen cyanide?
A
It acts as a catalyst to make the C=O bond more polar which enables the CN- ion to act as an effective nucleophile
10
Q
When an ester is hydrolysed how are the products named?
A
Everything before the C=O bond forms part of the carboxylic acid, everything after the C=O bond forms part of the alcohol
11
Q
What products are formed when methyl propanoate is hydrolysed using water and an acid catalyst?
A
Propanoic acid + methanol
12
Q
What is formed when methyl propanoate is hydrolysed using NaOH?
A
Sodium propanoate + methanol
13
Q
What is Brady’s reagent?
A
2,4-DNP, orange transparent mixture
14
Q
What does Brady’s reagent test for?
A
- Aldehydes and ketones, when 2,4-DNP is added to a solution containing an aldehyde or ketone, a yellow/orange precipitate is formed
- No precipitate is observed with a carboxylic acid or an ester despite them having the C=O bond
15
Q
After a positive Brady’s reagent test what test would you use to distinguish between an aldehyde and ketone?
A
The precipitate formed from the reaction of 2,4-DNP and the aldehyde/ketone can be collected by filtration and purified by crystallisation, this can then be dried and the accurate melting point of the pure product can be measured through experiment
- The melting point for the precipitate can then be compared to database values, this tells you whether it is an aldehyde or a ketone
16
Q
What is Tollen’s reagent?
A
A colourless chemical that can be used to distinguish between a ketone and an aldehyde
17
Q
What is the method for making Tollen’s reagent?
A
- Sodium hydroxide solution is added to silver nitrate solution until a brown precipitate is formed
- Dilute ammonia is added dropwise until the precipitate redissolves
18
Q
How does Tollen’s reagent distinguish between a ketone and an aldehyde?
A
- Tollen’s reagent is a weak oxidising agent, Tollen’s reagent react with aldehydes and a redox reaction takes place
- The silver ions are reduced and the aldehyde functional group is oxidised
- Ag+(aq) + e- → Ag(s) Silver ions are reduced to silver metal which forms a precipitate, this appears as a silver mirror
- RCHO + [O] → RCOOH aldehyde is oxidised to a carboxylic acid
19
Q
What is the observation when Tollen’s reagent is added to an aldehyde?
A
A silver mirror is observed
20
Q
What is the general formula of a carboxylic acid?
A
CnH2n+1COOH
21
Q
What is the general formula for an aldehyde?
A
CnH2n+1CHO
22
Q
What is the trend in solubility as carboxylic acids get bigger?
A
- The small carboxylic acids are soluble in water and other polar substances. This is because hydrogen bonds can be formed between the carboxylic functional group and the water molecules
- As the hydrocarbon chain of the carboxylic acid increases in size, the solubility decreases
- This is because only the polar carboxylic acid functional group can form hydrogen bonds with the water molecules
23
Q
What happens when a carboxylic acid is dissolved in solution?
A
It partially ionises in solution to form a carboxylate ion and an H3O+ ion
24
Q
What is the difference between a weak acid and a strong acid?
A
- A weak acid has a lower concentration of H+ ions, however because dissociation is an equilibrium, when the ions of a weak acid are reacting, more are produced as the ions are used up as the concentration of the products decreases the position of equilibrium shifts towards the products. This means that the same moles of H+ ions will be used in a reaction using both a weak acid and a strong acid but the strong acid will be instantly ionised whereas the weak acid gradually ionises as the reaction takes place
- This means that the rate of reaction will be slower when using the same concentration of a weak acid as a strong acid but they will both produce the same moles of product if the same volume of both is used
25
What products are formed when sodium reacts with ethanoic acid?
2Na + 2CH3COOH → 2CH3COONa + H2
26
What products are formed when magnesium oxide reacts with methanoic acid?
MgO(s) + 2HCOOH(aq) → (HCOO)2Mg(aq) + H2O(l)
27
What products are formed when potassium hydroxide reacts with propanoic acid?
KOH(aq) + CH3CH2COOH(aq) → CH3CH2COOK(aq) + H2O(l)
28
What products are formed when sodium carbonate reacts with methanoic acid?
Na2CO3(s) + 2HCOOH(aq) → 2HCOONa(aq) + H2O(l) + CO2(g)
29
How are esters named?
- Everything before the ester linkage is part of the acid and everything after the ester linkage is part of the alcohol
- For example an ester: CH3COOCH3 is named methyl ethanoate
30
What reactants are used to produce an ester?
A carboxylic acid and an alcohol are heated gently in the presence of a sulfuric acid catalyst, an ester and a water molecule are produced
31
What are the chemical properties of an ester?
Esters have low boiling points as they aren't able to form hydrogen bonds between molecules, this means that esters are very volatile
32
How can esters be separated from the reaction mixture?
Using distillation as the esters are very volatile meaning they can easily be evaporated off and then recollected by condensing the gas produced
33
Why can't phenols be used instead of an aliphatic alcohol?
The rate of reaction is too slow, phenols have the delocalised ring making them much more stable than aliphatic alcohols
34
What is formed in the reaction between ethanoic anhydride and methanol?
- Methyl ethanoate + ethanoic acid
| - (CH3CO)2O + CH3OH → CH3COCH3 + CH3COOH
35
What does the hydrolysis of an ester form?
A carboxylic acid and an alcohol
36
What are the benefits and cons of producing an ester from an acid anhydride?
The reaction is not reversible meaning a higher yield of the ester product is obtained than using a carboxylic acid
37
What happens when an ester is refluxed and what catalyst is required?
When esters are refluxed with a catalyst of hot aqueous acids, such as dilute H2SO4 or dilute HCl, the ester will decompose reversibly into a carboxylic acid and an alcohol
38
What happens when an ester is refluxed with a hot alkali such as NaOH?
- When an ester is heated under reflux with a hot alkali, the ester will decompose into an alcohol and a carboxylate salt
- This reaction is not reversible
- This reaction can be used to make soaps
39
What is the reaction to produce an acyl chloride?
CH3COOH + SOCl2 → CH3COCl + SO2 + HCl
40
What do acyl chlorides produce when they react with alcohols?
- They react with alcohols to produce an ester and HCl
- CH3COCl + CH3CH2OH → CH3COOCH2CH3 + HCl
- This reaction is not reversible so therefore has a higher yield of ester than the reaction using a carboxylic acid
41
How do you name an acyl chloride?
Count the number of carbons in the carbon chain and add to the suffix -oyl chloride
42
What do acyl chlorides produce when they react with water?
- A carboxylic acid
| - CH3COCl + H2O → CH3COOH + HCl
43
What is the observation of reactions with acyl chlorides that produce HCl?
Steamy fumes are given off
44
What happens when an acyl chloride reacts with ammonia?
- A primary amide is produced
- CHCOCl + 2NH3 → CHCONH2 + NH4Cl
- Solid ammonium chloride is produced and ethanamide is produces as a white smoke
45
What happens when an acyl chloride reacts with an amine?
- A secondary amide is produced
- CH3COCl + CH3CH2NH2 → CH3CONHCH2CH3 + HCl
- Ethylamine must be a cold concentrated solution
- N-ethylethanamide is a white solid
46
What is N-ethylethanamide?
CH3CONHCH2CH3
47
What evidence is there against Kekule's model of benzene?
- Unlike alkenes, benzene is resistant to addition reactions, this means that when bromine water is added to benzene it does not discolour like it would if added to an alkene
- Bond enthalpy of hydrogenation of benzene is much more stable than predicted
- All six carbon bonds in benzene are the same length, whereas if there were three C=C bonds and three C-C bonds like Kekule's model suggests then they would be different lengths
48
Compare the enthalpy change of the hydrogenation of benzene compared with Kekule's predicted value
The enthalpy change of hydrogenation of cyclohexene is -120kJmol-1, this means that the predicted enthalpy change of hydrogenation of Kekule's model should be -360kJmol-1 as Kekule's model has 3 C=C double bonds. However, experimentally it is found that the enthalpy change of hydrogenation of benzene is -208kJmol-1 meaning that the reaction is less exothermic meaning more energy is required to start the reaction. This means that benzene is more stable than predicted and therefore Kekule's model is inaccurate
49
How does resistance to reaction of benzene provide evidence against Kekule's model?
Kekule's model was predicted to undergo similar reactions to alkenes as the model has 3 C=C bonds. It was found that benzene doesn't undergo addition reactions as when bromine water was added to benzene it remained orange. This was evidence against Kekule's model
50
How are the bond lengths of benzene evidence against Kekule's model of benzene?
X-ray diffraction techniques have shown that all 6 carbon bonds in benzene are 0.140nm which is between a C-C bond at 0.147nm and a C=C bond at 0.135nm. Kekule's model suggested that benzene had 3 shorter C=C bonds and 3 longer C-C bonds, all 6 bonds being the same length disproves Kekule's model
51
Describe the delocalised structure of benzene
Each of the six carbon atoms donates one electron from its p-orbital to form a ring of delocalised electrons above and below the plane of the molecule. The electrons in the rings can move freely within the ring and not belong to a single. Therefore, all the bonds in this benzene ring are identical meaning they are the same length disproving Kekule's model
52
How does benzene undergo hydrogenation?
H2 molecules are added to the benzene molecule, addition reactions occur which destroy the delocalisation of the benzene ring and form a cycloalkane as hydrogens are added all around the benzene molecule
53
When benzene undergoes a double substitution reaction how is the product named?
The group that was added first will be on the first carbon
54
Summarise the nitration of benzene with an equation
C6H6 + HNO3 → C6H5NO2 + H2O
55
What type of reaction is the nitration of benzene?
Electrophilic substitution
56
Describe how nitration of benzene is carried out experimentally
- Concentrated nitric acid and the sulfuric acid catalyst are mixed togetehr in a flask held in an ice bath
- The benzene and the mixture of nitric acid and sulfuric acid are added to a reflux condenser, this keeps the mixture at 50°C and prevents further substitution reactions occurring
57
What is the sulfuric acid catalyst used for in the nitration of benzene?
The sulfuric acid catalyst is used to generate the NO2+ electrophile from the nitric acid
- HNO3 + H2SO4 → NO2+ + HSO4- + H2O
- HSO4- + H+ → H2SO4
58
What molecule is required for the nitration of benzene?
Benzene doesn't react directly with halogens as the aromatic ring is too stable, a halogen carrier such as AlCl3, FeCl3 or Fe for chlorination and AlBr3, FeBr3 or Fe for bromination
59
What is the equation for the reaction to generate the Br+ electrophile?
Br2 + FeBr3 → Br+ + FeBr4-
The FeBr3 is regenerated at the end of the halogenation as the H+ removed from the benzene ring reacts with FeBr4-
- FeBr4- + H+ → FeBr3 + HBr
60
How is the length of the carbon chain increased?
By Friedel-Crafts reactions
61
What are the two types of friedel crafts reactions?
Alkylation and acylation
62
What are the conditions for acylation?
The reaction mixture is heated under reflux for around 30 minutes at 60°C with an AlCl3 catalyst
63
What is the general formula of an acyl chloride?
RCOCl
64
What is the product of an acylation reaction?
C6H6 + RCOCl → C6H5COR
65
What is C6H5CH2CH2OH called?
Phenylethanol
66
How does phenol dissociate in water?
Phenol is a weak acid, it partially dissociates in water C6H5OH + H2O → C6H5O- + H3O+
67
What is the reaction between phenol and NaOH?
C6H5OH +NaOH →C6H5O-Na+ + H2O
68
How does the reactivity of phenol compare to the reactivity of benzene?
Phenol is more reactive than benzene as the p-orbital electrons from the oxygen of the hydroxyl group are drawn into the ring of delocalised electrons making the pi-system of the aromatic ring becomes more nucleophilic (more electron dense)
69
Does benzene have a higher or lower electron density between carbon atoms than an alkene?
Lower, this is why there is no reaction between bromine water and benzene
70
What directing effect do OH groups have?
2,4 as the hydroxyl group pushes electrons into the pi-system, this makes substitution reactions mainly occur on the 2 and 4 positions of the aromatic ring
71
Why can phenol react directly with Br2 but benzene can't?
The aromatic ring of phenol is more electron dense meaning it can induce a dipole in the non-polar bromine molecule. This means phenol can undergo direct halogenation, unlike benzene
72
What are the observations of the reaction between C6H5OH and 3Br2?
A white precipitate of 2,4,6-tribromophenol is produced that smells of antiseptic
73
What is the equation for the reaction between dilute HNO3 and phenol?
- C6H5OH + HNO3 → C6H4(NO2)OH + H2O
| - The products are a mixture of 2-nitrophenol and 4-nitrophenol
74
What are the products of the reaction between concentrated HNO3 and phenol?
- C6H5OH + 3HNO3 → C6H2(NO2)3OH + 3H2O
| - 2,4,6-nitrophenol is produced
75
What directing effect does an NH2 group have?
2,4 as it pushes electrons into the pi system, this makes substitution reactions occur on the 2 and 4 positions of the aromatic ring
76
What directing effect does an NO2 group have?
3 as the NO2 group withdraws electrons from the pi system and makes substitution reactions occur on the 3 position of the aromatic ring
77
Does phenylamine require a halogen carrier when reacting with Br2?
No as the NH2 group pushes electrons into the aromatic ring making the ring able to induce a dipole in the Br2 molecule and allow a substitution reaction to occur
78
Does nitrobenzene require a halogen carrier to react with Br2?
Yes, it requires FeBr3 or AlBr3 as the NH2 group withdraws electrons from the pi system making the ring less electron dense and therefore unable to induce a dipole in the non-polar Br2 molecule. This means that nitrobenzene can't undergo a substitution reaction with Br2 without a halogen carrier
79
What is the equation for the reduction of pentan-2-one?
CH3C=OCH2CH2CH3 + 2[H] → CH3CH(OH)CH2CH2CH3
80
What is the product of a reduction reaction in which the intermediate reacts with an ethanol molecule?
An alcohol and -OCH2CH3
81
What is the product of the reaction between (CH3)2CO and HCN?
(CH3)2COHCN
82
What is required for the reaction between (CH3)2CO and HCN?
Acidic conditions, this is provided by the HCN as it dissociates i solution to produce H+ and CN- ions. The reaction needs to be acidic as the carbonyl compound becomes more reactive as the polarity of the C=O bond is increased by the acidic conditions
83
What is a primary amine?
RNH2, a nitrogen atom attached to 2 hydrogen atoms and one R group
84
What is a secondary amine?
RR'NH, a nitrogen atom attached to one hydrogen atom and two R groups
85
What is a tertiary amine?
RR'R''N, a nitrogen atom attached to three R groups
86
How do you name an amine?
Name the alkyl chains with N- and then name the longest chain as part of the amine
- For example: CH3CH2CH2-NH(CH3) is N-methylpropylamine
- CH3CH2CH2-NCH2CH3(CH2CH3) is N,N-diethyl propylamine
87
What is a Lewis base?
An electron pair donor (a nucleophile), amonia and amines have a lone pair on the N making them Lewis bases
88
What is a Bronsted-Lowry base?
A proton acceptor, ammonia and amines can accept H+ on the nitrogen atom and therefore are also Bronsted-Lowry bases
89
What does methylamine (CH3NH2) form when it combines with a proton?
Methylammonium ion. CH3NH3+
90
What is produced in the reactions between ethylamine and HCl, HNO3 and H2SO4?
- CH3CH2NH2 + HCl → CH3CH2NH3+Cl-
- CH3CH2NH2 + HNO3 → CH3CH2NH3+NO3-
- CH3CH2NH2 +H2SO4 → (CH3CH2NH3+)2SO42-
91
What is the general formula of an amino acid?
NH2CHRCOOH
92
What is a zwitterion?
Where the carboxyl group of the amino acid donates a proton to the amine group to form NH3+CHRCOO-
93
What is the isoelectric point of a zwitterion?
Where there is no net electrical charge due to each zwitterion having an internal balance of charge, the isoelectric point is where the zwitterion is formed, this varies for each amino acid
94
What happens to an amino acid when pH is decreased to 1?
H+ concentration increases, the NH2 group accepts a proton and a positive ion is produced
95
What happens when amino acid pH is increased to 13?
OH- concentration is increased, the COOH group donates a proton to the OH- ion, this produces a negative ion and a water molecule
96
What is produced in the reaction between an amino acid and HCl?
NH2CHRCOOH + HCl → NH3+Cl-CHRCOOH
97
What is the general formula of an amide?
RCONH2
98
What is a primary amide?
Where the nitrogen atom has 2 hydrogen atoms attached and one acyl group
99
What is a secondary amide?
Where the nitrogen atom is attached to one acyl group, one alkyl group and one hydrogen atom
100
What is a tertiary amide?
Where the nitrogen atom is attached to one acyl group and two alkyl groups
101
How do you name an amide?
- The R group attached to the carbon that is bonded to the oxygen, is named just before the amide suffix. For example a CH3 group attached to the C=O and the nitrogen group attached to two hydrogens is ethanamide.
- The group attached to the N is named as N-ethyl if it is a C2H5 group attached
102
Name the amide with a structural formula of CH3CONHCH2CH3 and an amide with the formula CH3CONHCH3
N-ethylethanamide
| N-methylethanamide
103
Name the amide with the structural formula HCONH2
Methanamide
104
Name the amide with the structural formula CH3CH2CONH2
Propanamide
105
What is an optical isomer?
Isomers that are non-superimposable mirror images of each other, each optical isomer interacts with light in a different way. Optical isomerism is a form of stereoisomerism
106
What are optical isomers of each other known as?
Enantiomers
107
What prefix will an enantiomer be given if the enantiomer rotates the plane of polarised light clockwise?
+, it is - if the polarised light rotates in the anti-clockwise direction. This can't be determined from structure of the enantiomer, only by experiment
108
What is a racemic mixture?
A 50:50 mixture of enantiomers, a racemic mixture will have no effect on polarised light as the rotation from the two enantiomers cancel each other out
109
How are chiral carbon marked on displayed/skeletal formula?
With a *
110
What is a chiral carbon?
A carbon with 4 different groups attached to it, for an optical isomer to be formed in an organic compound, there has to be chiral carbon present
111
What is condensation polymerisation?
Where two monomers with different functional groups react to form a form a polymer and release a small molecule, often a water molecule
112
If a monomer contains C=C will it form an addition or condensation polymer?
An addition polymer, if a monomer contains two different functional groups or more than one monomer is present then a condensation polymer can be formed
113
How is a polyester formed?
Polyesters are formed in the reaction between a dicarboxylic acid and a diol. The carboxylic acid group on one side of the dicarboxylic acid reacts with the OH group on the adjacent side of the diol. This forms an ester linkage and a water molecule. This happens many times and produces a long chain molecule
114
When a condensation reaction occurs, is the O removed from the alcohol or the carboxylic acid?
The carboxylic acid, this means that when drawing the polymer structure you should draw leave the O on the alcohol side but remove it from the carboxylic acid side
115
How is a polyamide produced?
A polyamide is produced when a dicarboxylic acid and a diamine undergo a condensation reactio, the OH group from the carboxylic acid reacts with the H from the amine group, an amide link a water molecule are produced. This happens between many molecules and a long-chain molecule is produced =
116
What is a use of polyester?
It is used in clothing
