18: Further Organic Chemistry Flashcards
(173 cards)
1
Q
What is an arene?
A
Aromatic hydrocarbons
2
Q
What are the two structures of benzene?
A
Kekulé and delocalised structure
3
Q
What is the molecular formula of benzene?
A
C6H6
4
Q
What is the structure of benzene?
A
C6H6 Planar molecule containing a ring of six carbons each with a H attached
Hexagon shape
5
Q
What is notable about the bonds in benzene?
A
All bonds are the same length
Inbetween length of single and double bond
6
Q
Where are the electrons in benzene?
A
Delocalised above and below the plane of the ring
7
Q
What does the delocalisation do to benzene?
A
Increases the stability of the molecule
8
Q
What is the Kekulé structure of benzene?
A
Alternating single and double bonds in a hexagon structure
9
Q
What does the bond length suggest about the structure?
A
Kekulé model suggests 2 different bond lengths
Therefore suggests delocalsied structure
10
Q
How was the bond length in benzene found?
A
X-ray diffraction
11
Q
What are the bond angles in benzene?
A
120°
12
Q
What is the structure of the delocalised model of benzene?
A
Each carbon forms three σ bonds (2C 1H) p-orbital remaning is above and below plane of ring which overlap sideways to form ring of π-bonds which are delocalised
13
Q
Where are delocalised electrons in benzene?
A
Two ring-shaped clouds above and below plane of the carbons
14
Q
What is the length of bonds in the delocalised structure?
A
All the bonds are the same length
15
Q
Why are electrons delocalised in the delocalised structure of benzene?
A
Electrons do not belong to a specific atom
16
Q
What is the enthalpy change of hydrogenation?
A
Enthalpy change of the reaction whereby hydrogen gas is added across a C=C
17
Q
How do hydrogenation enthalpies disprove the Kekulé structure?
A
Cyclohexene with 1 double bond has -120 kJ/mol
Kekulé structure would expect to have -360 kJ/mol
However experimental value is -208 kJ/mol
18
Q
Why is the enthalpy of hydrogenation of benzene less negative that expected?
A
More energy needed to break the bonds than expected in the Kekulé
More stable than Kekulé due to delocalised ring of electrons
19
Q
What was used to compare the structures of benzene?
A
X-ray diffraction
IR spectra for bonds present
Enthalpy of hydrogenation
Whether follows standard electrophillic addition
20
Q
What occurs when bromine water is added to benzene?
A
No colour change seen
21
Q
Why does benzene not undergo addition reactions?
A
Delocalised π-bonds mean addition would decrease stability
Spread out negative charge rather than one area of high electron density, doesn’t attract electrophiles as much
22
Q
What is the equation of benzene burning in air?
A
2C6H6 + 15O2 → 12CO2 + 6H2O
23
Q
What occurs when benzene is burnt in air?
A
Very smoky flame - too little to burn benzene completely
24
Q
What is the preffix of NO2?
A
nitro-
25
What is the name of a benzene ring with an -OH group on one of the carbons?
Phenol
26
What is the name of a benzene ring with a -NH2 substituent?
Phenylamine
27
How are benzene compounds named when there are more than one group added?
If all are same, pick group to start which gives smallest numbers when counting round
If groups are different, start from molecule which gives it the suffix and count round to give smallest numbers
28
What is the name of benzene with a single -CH3 group bonded?
Methylbenzene or Toluene
29
What is the prefix of bezene when it is bond to another compound?
Phenyl-
30
State the reactivity of benzene compared to alkene
Stability of delocalised electrons in ring means it is less reactive
31
Why does benzene have a sootier flame?
High C:H
32
What are the coniditons for the hydrogenation of benzene?
Raney nickle catalyst
200°C
33
What type of reaction does benzene undergo with electrophiles?
Electrophilic substitution
NOT addition
34
What is the mechanism for the electrophilic substitution reaction?
Benzene delocalised ring reacts with electrophile, breaks ring (arrow from ring to E+)
An unstable intermediate forms (ring stops either side of carbon, replace by +, show E and H bonded to carbon and arrow from C-H to +)
H+ is lost, delocalised ring is reformed
E = electrophile
35
What is an electron withdrawing group?
Group that draws electron density from neighboroughing atoms to itself
36
What is an electron donating group?
Group which donates electrons into a delocalised structure
37
List some common electron withdrawing groups
NO2, CO2, ester
38
List some electron donating groups
OH, NH2
39
Why can benzene only react with very positively charged species?
Electrons are spread and in a low-density
Therefore high + charge needed for the ring to attack
40
What can be used to make stronger electrophiles?
Halogen carrier
41
How does a halogen carrier work?
Accepts a lone pair of electrons from a halogen atom in halogenoalkane or X2
Lone pair is pulled away, polarisation in molecule increases and sometimes carbocation / X+ forms
Makes the electrophile stronger
42
Name the standard halogen carriers
Aluminium halides
Iron halides
Iron
43
What are the conditions for the bromination of benzene?
Anhydrous iron/iron (III) bromide catalyst
Dry benzene and liquid bromine
Warmed
44
What does a halogen carrier do in a bromination reaction?
Breaks Br2 to Br+ and FeBr4
Ring attacks Br+
Electrons form C-H goes into ring and Fe-Br electrons go to the lost H
Forms bromobenzene + HBr + FeBr3
45
What are the reactions for the bromination of benzene?
FeBr3 + Br2 → [FeBr4]- + Br+
C6H6 + Br+→ C6H5Br + H+
H+ + [FeBr4]- → FeBr3 + HBr
46
What is alkylation?
Addition of an alkyl group (e.g. methyl, ethyl etc.) onto the benzene ring
Generally uses a Friedel-Crafts reaction
47
What are Friedel-Crafts reactions used for?
Forms C-C bonds
48
What are the conditions and reagents for a alkylation reaction?
Benzene + halogenoalkane
Anhydrous AlCl3 catalyst
Reflux
49
What occurs when a chloroalkane reacts with AlCl3 in a Friedel-Crafts reaction?
R-Cl + AlCl3 → R+ + [AlCl4]-
Cl lone pair attacks Al and R-Cl breaks
50
What are the stages in an alkylation Friedel-Crafts reaction?
R-X + AlCl3 → R+ + [AlCl3X]-
C6H6 + R+ → C6H5R + H+
H+ + [AlCl3X]- → HX + AlCl3
Overall: C6H6 + R-X → C6H5R + HX
51
What is an acylation reaction?
Addtion of an acyl group (RC=O) onto a benzene ring
This is a Friedel-Crafts reaction
52
What are the reagents and conditions for an acylation?
Dry acyl chloride and benzene
Anhydrous AlCl3
Reflux
53
What is the overall reaction in an acylation reaction?
C6H6 + RC=OCl → C6H5RC=O + HCl
54
What are the stages of reactions in the acylation Frieldel-Crafts reaction?
RCOCl + AlCl3 → RC+=O + [AlCl4]-
C6H6 + RC+=O → C6H5COR + H+
H+ + [AlCl4]- → HCl + AlCl3
Overall: C6H6 + RCOCl → C6H5COR + HCl
55
What is nitration of benzene?
NO2 is added to a benzene ring
56
What are the conditions of the nitration of benzene?
conc H2SO4 + conc HNO3
50°C for benzene
57
Which electrophile is used for the nitration of benzene?
NO2+
58
What is the name of the NO2+ ion?
Nitronium ion
59
How is the nitronium ion produced for the benzene substitution?
HNO3 + H2SO4 → H2NO3+ + HSO4-
H2NO3+ → NO2+ + H2O
60
What is the overall reaction between the nitronium ion and benzene?
C6H6 + HNO3 → C6H5NO2 + H2O
H2SO4 not included as it is a catalyst
61
Why are temperatures not above 50C reccomended for the nitration of benzene?
Temperatures not above that as it causes more than 1 nitration
62
What is the molecular formula of phenol?
C6H5OH
63
How likely is phenol to undergo electrophilic substitution compared to benzene?
Phenol is more likely to undero electrophilic substitution than benzene
64
Why is phenol more likely to undergo electrophilic substitution?
Lone pair in p-orbital of oxygen overlaps with π-bonds in benzene ring
Lone pair from oxygen is partially delocalised into π-system
Increases electron density in ring so more lilkely to be attacked by electrophiles
65
What occurs when phenol is added to bromine water?
Bromine water is decolourised
Occurs as phenol is more reactive than benzene
66
What is the solubility of ethanol and phenol in water?
Phenol - slightly soluble
Ethanol - highly soluble
67
What is the pH of ethanol and phenol?
Ethanol - neutral
Phenol - 4-5
68
How does phenol react with NaOH?
C6H5OH + NaOH → Na+ C6H5O- + H2O
69
What are the procedure for the production of aspirin?
Salicyclic acid + Ethanoic anhydride + Phosphoric acid
Warm to 50°C for 15 minutes then cool on ice, forms aspirin crystals
Filter crystals under reduced pressure
Recrystallise the aspirin in a mix of water and ethanol
70
What is the reaction to form aspirin?
Salicyclic acid + ethanoic anhydride → Aspirin + ethanoic acid
C7H6O3 + C4H6O3 → C9H8O4 + CH3COOH
Look at the structural formula
71
How does phenol react with ethanoic anhydride?
Esterification reaction
72
Why is ethanoic anhydride somtimes used instead of an acyl chloride?
Reacts in the same way
Cheaper and safer as not as reactive
73
What is the molecular formula of phenylamine?
C6H5NH2
74
What is an amine?
Compound where a hydrogen in ammonia is replaced by R
Amines contain functional group -NR2 (alkyl or H)
75
What are the types of amines?
Primary
Secondary
Tertiary
Quaternary
76
What does aliphatic mean?
Compounds without any benzene ring structures
77
What type of amine is phenylamine?
Primary amine - only one of hydrogens replaced by organic group
78
What gives phenylamine its unique properties?
Free electrons on nitrogen are donated/delocaised into the ring system
Therefore acts differently to typical amines
79
Is NH2 an electron donating or withdrawing group?
Electron donating group
80
How reactive is phenylamine compared to benzene and why?
Phenylamine is more reactive than benzene
Nitrogen's lone pair increases electron density around the ring
Therefore attacks electrophile better
81
What are the stages of the production of phenylamine from benzene?
Nitration of benzene
Reduction of nitro group to amine
82
How is nitrobenzene converted to phenylamine?
Nitrobenzene, tin and conc hydrochloric acid mixed
Heated under reflux at 100°C
Cooled and excess NaOH added
Steam distillation of mix and then separation from water using brine and drying agent added (anhydrous potassium carbonate)
Purified by distillation
83
What are the conditions for reducing nitrobenzene?
1) Reflux mix of nitrobenzene, tin andconc hydrochloric acid
2) NaOH added
84
Why is phenylamine slightly soluble in water?
Can form hydrogen bonds
Benzene breaks more H-bonds than formed betwen water and NH2
85
Why is phenylamine less water soluble than phenyl ammonium salt?
Ammonium salt is ionic/charged, phenylamine is not
Lone pair on N in phenylamine is delocalisde into ring system
86
What is a test for phenol?
Reacting phenol with FeCl3 forms a purple solution
87
What is used as an alternative to phenol and why?
methyl 4-hydroxybenzoate
Reacts similarly but it is less dangerous
88
What is the purpose of the Grignard reaction?
Reaction to extend the carbon chain
89
What are the conditions of producing the species for the Grignard reaction?
Dry ether
R-I (iodine)
Mg
90
What is the species which is made for the Grignard reaction?
-R
91
What occurs when a Grignard reactant is used to react with carbon dioxide?
Produces carboxylic acid
CO2 + -R → R-COOH
92
How are amines typically made?
Heating a halogenoalkane with excess ethanolic ammonia
93
What is the problem with heating a halogenoalkane with excess ethanolic ammonia?
Produces mix of primary, secondary and tertiary amines and quaternary ammonium salts
94
Why is there a mix when you heat a halogenoalkane with excess ethanolic ammonia?
Lone pair of electrons on the amine
Acts as a nucleophile for nucleophilic substitution with any halogenoalkane causes substituted amines to be produced
95
How many hydrogens and R groups are on a primary amine?
2 hydrogens
1 R group
96
How many hydrogens and R groups are on a secondary amine?
1 hydrogen
2 R groups
97
How many hydrogens and R groups are on a tertiary amine?
3 R groups
98
How do you name secondary amines such as C2H5-NH(CH3)?
N-methylethylamine
N-smaller chain then followed by longer name
99
Which group takes priority in naming amino acids?
Acid group has higher priority so forms suffix
Amino groups are relegated to a prefix
100
How polar is the N-H bond?
Polar but not as polar as OH bond
101
How soluble are amines?
Smaller amines are soluble as they are polar and N-H can form hydrogen bonds
Larger ones cannot as they disrupt too many H-bonds
102
What occurs to amines in water?
R-NH2 + H2O → R-NH3+ + OH-
Therefore becomes alkaline
103
What is the smell of amines?
"Fishy" smell
104
What are amines in the Bronsted-Lowry theory?
Bronsted-Lowry bases
Proton acceptors
105
What does the ability of an amine to act as a base depend on?
Availability of lone pair on N atom to accept H+
Increased electron density of lone pair on N means it is a stronger base
106
How are the different amines ordered in strength of base from low to high?
Aromatic → primary → secondary → tertiary
107
Why are amines more basic the more R groups bound to it?
Inductive effect of alkyl groups means it pushes electron density towards the nitrogen
The higher the electron density of the lone pair on the N, the stronger the base
108
Why are aromatic amines less basic?
Lone pair on N partially delocalised into benzene ring
Reduces electrons on N atom, and therefore less likely to offer to H+ so it is a weaker base
109
What is the most common way for producing an amine?
Producing a nitrile from a halogenoalkane
Reducing to an amine
110
What are the methods reducing nitriles to amines?
LiAlH4 in dry ether followed by dilute acid
Nickle catalyst, hydrogen, high temp and pressure
111
Why is LiAlH4 not used in industry?
Too expensive for industry
V reactive with any water
112
Why are amines nucleophiles and therefore how can they react?
Lone pair of electrons
Nucleophilic substitution reaction
113
How do amines react with acids?
R-NH2 + HA → R-NH3+ A-
114
What is the colour of the [Cu(H2O)6]2+ complex?
Blue
115
What is a test for amines?
Add small amount of amine to copper(II) sulphate solution
Pale blue precipitate forms
XS amine gives a deep blue solution
116
What do amines do to copper (II) sulphate?
Amine acts as base,deprotonates H2O to OH-
Forms [Cu(OH)2(H2O)4] which is an insoluble pale blue precipitate
More amine replaces ligand to form deep blue [Cu(R-NH2)4(H2O)2]2+
117
How do primary amines react with acyl chlorides?
Forms a secondary amide
118
What are the requirments for reacting acyl chlorides with amines?
Concentrated solution of amine
119
What is observed when an amine reacts with an acyl chloride?
Violent reaction occurs
Produces a solid, white mixture
120
What do amides contain?
Functional group -CONH2
121
Why do amides react differently than amines?
Carbonyl pulls electrons away from the rest of the group
122
What types of amides are there?
Primary amides
N-substituted amides depending on number of carbonds the nitrogen is bonded to
123
What is the suffic of amide?
-amide
124
How are N-substituted amides named?
N-alkyl-
then -amide
125
How can amides be made?
Reacting acyl chloride with amnmonia or a primary amine
126
What are the conditions for producing amides?
Acyl chlride + conc ammonia or primary amine
Room temp
127
What is condensation polymerisation?
Monomers being joined together with the loss of a small molecule
128
What do monomers have to contain for condensation polymerisation?
At least two functional groups
Normally involves two differents types of monomer
Each reacts with group on another monomer to form a bond
129
What are amide links?
-CONH- which forms between a carboxlyic acid and amino groups
Water lost each time one forms
130
What are polyamides?
Monomers are usually dicarboxylic acids and diamines
Forms -CONH- links
Water lost each time it forms - condensation reaction
131
What is an amino acid?
Molecule that has amino group (NH2) and carbocxyl group (COOH)
132
What is the structure of amino acids?
H2N - CH(R) - COOH
R is different based on the amino acid
133
What does amphoteric mean?
Molecule which is able to act as an acid and a base
134
How are amino acids amphoteric?
Amino groups can act as a base
Carboxyl (COOH) group can act as an acid
135
What is a zwitteron?
Overall neutral molecule with both positive and negative charges in different parts of the molecule
136
What is the isoelectric point?
pH when the overall charge on a molecule is zero
137
When can amino acids act as zwitterions?
Isoelectric point
This depends on the R group
138
What occurs to amino acids in more acidic than isoeletric point conditions?
NH2 group is protonated to NH3+
139
What occurs to amino acids in more basic conditions than the isoleletric point?
COOH group is deprotonated to COO-
140
What is the composition of a zwitterion of an amino acid?
Amino group protonated NH2→ NH3+
Carboxyl group deprotonated COOH → COO-
141
When will amino acids have their isoeletric point at around pH 7 ?
When there are the same number of carboxyl and amino groups
142
What are the amino acids found in nature?
2-amino acids (amino group on the second carbon, first is carboxyl)
143
What groups are attached to the second carbon of a 2-amino acid?
Carboxyl (COOH)
Amino (NH2)
Hydrogen atom
R group
144
Which amino acid has a hydrogen atom as the R group?
Glycine
145
What is the optical activity of 2-amino acids?
Chiral molecules
Chiral centre on 2nd carbon
146
What occurs to plane-polarised, monochromatic light if it shone through an aqeuous solution of one enantiomer of a 2-amino acid?
Plane of the light gets rotated because of the chiral carbon
147
What is the exception to the chirality of 2-amino acids?
Glycine
R group is hydrogen so no chiral centre
148
What does achiral mean?
Not a chiral molecule
149
What are proteins?
Polymers of amino acids
Condensation polymers
150
What are the links which form between amino acids in proteins?
Peptide links
Same as amide links
151
How does a peptide link form?
Carboxyl group of one amino acid reacts with amino group of adjacent one
One water lost - Condensation reaction
152
How are proteins hydrolysed?
Hot aqueous HCl needed
Produces ammonium salts of amino acids which is then neutralised using a base
153
Why would you want to hydrolyse proteins?
Break into constiutent amino acids
Allows for identification of amino acids which make up a protein
154
What are polyesters?
Polymers formed between dicarboxlyic acid and diol monomers
Condensation polymers
155
What links form between dicarboxylic acids and diols?
Ester links
156
How do you find the monomers of a polyester from the repeat unit?
Break ester link between C - O
Add H or OH to both ends to find the monomers
157
How can unknown amino acids be identified?
Paper chromatography
158
Why is phenol more reactive than benzene?
Oxygen donates electron to the delocalised ring system
Occurs as Oxygen has lone pairs which overlap in same plane
Increases negative charge of teh ring so acts as a better nucleophile
159
What is the Rf Value?
Rf value = distance travelled by spot / distance travelled by solvent
160
What is the procedure of paper chromatography to determine unkown amino acids?
Draw pencil line near bottom of chromatography paper and put a conc spot of mix
Place paper in small beaker with small amount of solvent below spot of mixture with watch glass on top of beaker
When solvent is near the top take out of the solution
Spray with ninhydrin solutin or put in jar with iodine crystals, and circle positions
Calculate Rf and compare with known values
161
Why do amino acids move different amounts on the chromatography paper?
Different amino acids have different solubilities in the solvent
Therefore move at different rates so they separate
162
What is the solvent front?
Distance moved by the solvent
163
How are amino acids shown on paper chromatograms?
Ninhydrin solution
Dip into jar with iodine crystals, then circle positions with a pencil
164
When can you compare the Rf values for the amino acids?
Experiment done under standard conditions
165
What can be done other than paper chromatography to identify amino acids?
Thin-layer chromatography
166
What is the general formula of a Grignard reagent?
R-Mg-X
Where X is a halogen (usually iodine)
167
How are Grignard reagents made?
R-X + Mg → R-MgX
Reflux
Dry ether
168
How are carboxylic acids made using the grignard reaction?
Bubble CO2 through Grignard reagent in dry ether
Add dilute acid such as hydrochloric
169
How does the Grignard reagent form bonds with CO2?
new C-C bond forms between carbon in CO2 and C-Mg carbon in Grignard reagent
One of C=O bonds in CO2 broken to form -COO- which is protonated by the acid
170
How are alcohols made from aldehydes and ketones by the Grignard reaction?
new C-C bond forms between C in C-Mg and C=O carbon in the carbonyl
Causes C=O to break and forms -OH
171
What is the procedure for making an alcohol from a ketone/aldehyde by the Grignard?
Carbonyl compound added to the Grignard reagent in dry ether
Dilute acid is then added
172
What type of alcohol is formed in the Grignard reagent reacting with an aldehyde or ketone?
Aldehyde - secondary alcohol
Ketone - tertiary alcohol
173
Why is the pH of phenol slightly acidic?
Phenoxide ion - C6H5O-
This ion is stable due to the delocalisation of the lone pair
Therefore dissociates more readily in water
