Halogenoalkanes Flashcards
(170 cards)
1
Q
What is the suffix used for naming the longest carbon chain in halogenoalkanes?
A
-ane
2
Q
Which prefixes are used to name halogen atoms in halogenoalkanes?
A
fluoro, chloro, bromo, iodo
3
Q
How are multiple halogen atoms indicated in the naming of halogenoalkanes?
A
Using mono, di, etc., and listing halogens in alphabetical order
4
Q
What determines the numbering of the carbon chain in halogenoalkanes?
A
Locant numbers must be as low as possible
5
Q
What is the classification of the hydrocarbon chain in relation to the C-X functional group?
A
Primary, secondary, tertiary
6
Q
Define a primary halogenoalkane.
A
Has one carbon atom directly bonded to the carbon atom bonded to the halogen
7
Q
Define a secondary halogenoalkane.
A
Has two carbon atoms directly bonded to the carbon atom bonded to the halogen
8
Q
Define a tertiary halogenoalkane.
A
Has three carbon atoms directly bonded to the carbon atom bonded to the halogen
9
Q
Fill in the blank: A ______ halogenoalkane has one carbon atom bonded to the carbon that is bonded to the halogen.
A
primary
10
Q
Fill in the blank: A ______ halogenoalkane has two carbon atoms bonded to the carbon that is bonded to the halogen.
A
secondary
11
Q
Fill in the blank: A ______ halogenoalkane has three carbon atoms bonded to the carbon that is bonded to the halogen.
A
tertiary
12
Q
What is the structure of a primary halogenoalkane?
A
R - C - X where R is a carbon atom
13
Q
What is the structure of a secondary halogenoalkane?
A
R - C - R’ - X where R and R’ are carbon atoms
14
Q
What is the structure of a tertiary halogenoalkane?
A
R - C - R’ - R’’ - X where R, R’, and R’’ are carbon atoms
15
Q
True or False: Halomethanes are considered exceptions in the classification of halogenoalkanes.
A
True
16
Q
What is the boiling point trend of halogenoalkanes compared to alkanes with the same number of carbon atoms?
A
Halogenoalkanes have much higher boiling points than alkanes with the same number of carbon atoms due to increased RAM of halogen atoms and stronger van der Waals’ forces.
17
Q
What type of attractions do halogenoalkanes exhibit due to the polar nature of the C-X bond?
A
Permanent dipole-dipole attractions.
18
Q
Fill in the blank: The boiling point of halogenoalkanes increases when comparing different halogenoalkanes with the same number of carbon atoms, due to _______.
A
[the presence of different halogen atoms]
19
Q
What is the structural formula of 1-chloropropane?
A
C3H7Cl
20
Q
What is the boiling point of chloromethane?
A
-24.2 °C
21
Q
What is the boiling point of 1-bromobutane?
A
101 °C
22
Q
True or False: Tertiary halogenoalkanes have higher boiling points than primary halogenoalkanes with the same RMM.
A
False
23
Q
What is the boiling point of 2-bromo-2-methylpropane?
A
73 °C
24
Q
What is the RMM of 1-bromobutane and 2-bromo-2-methylpropane?
A
137
25
Explain the effect of branching on the boiling points of halogenoalkanes.
Increased branching results in weaker van der Waals' forces and lower boiling points due to fewer points of contact.
26
What is the boiling point of iodomethane?
42.4 °C
27
Fill in the blank: The structural formula of bromomethane is _______.
[CH3Br]
28
What is the boiling point of pentane?
36.1 °C
29
What is the nature of the C-X bond in halogenoalkanes?
The C-X bond is polar because the halogen atom is more electronegative than the carbon atom.
30
How does electronegativity change down Group VII?
Electronegativity decreases as Group VII is descended, making the C-X bond less polar.
31
What is the electronegativity of fluorine?
4.0
32
What is the electronegativity of chlorine?
3.0
33
What is the electronegativity of bromine?
2.8
34
What is the electronegativity of iodine?
2.5
35
Are halogenoalkanes soluble in water?
No, halogenoalkanes are usually insoluble in water.
36
In which type of solvents are halogenoalkanes soluble?
Halogenoalkanes are soluble in organic solvents like hexane and cyclohexane.
37
What was one of the first halogenoalkanes produced?
Dichlorodifluoromethane
38
Who developed dichlorodifluoromethane and when?
Developed in the 1930s by American chemist Thomas Midgley
39
What were the initial uses of dichlorodifluoromethane?
Used as a refrigerant for fridges and freezers as an alternative to ammonia.
40
What are the properties of dichlorodifluoromethane?
Non-toxic, unreactive, and non-flammable.
41
What are chlorofluorocarbons (CFCs)?
A series of compounds developed from dichlorodifluoromethane with various applications.
42
What applications were CFCs used for?
Aerosol propellants, solvents for dry cleaning, and blowing agents in the polymer industry.
43
What environmental concern arose from the use of CFCs?
Concern about their effect on the ozone layer.
44
What is ozone and its function?
Ozone (O3) is a gas that protects the earth by absorbing harmful ultraviolet radiation.
45
Where were large holes in the ozone layer discovered?
Over Antarctica.
46
What is the altitude range where CFCs can travel to reach the stratosphere?
15-40 km above the surface of the Earth.
47
What happens to CFC molecules in the stratosphere?
They absorb high energy ultraviolet radiation, causing heterolytic fission of the C-Cl bond.
48
What is produced from the heterolytic fission of the C-Cl bond in CFCs?
Chlorine radicals (Cl·)
49
What can chlorine radicals react with?
Ozone.
50
Initiation
51
Propagation
52
What is the first stage in organic synthesis?
The product is formed in the reaction mixture
53
What is the second stage in organic synthesis?
The product is extracted from the reaction mixture
54
What is the third stage in organic synthesis?
Purification of the crude product
55
What is synthesized in Stage 1?
Crude 1-bromobutane, C4H9Br
56
Which alcohol is used to synthesize 1-bromobutane?
Butan-1-ol, C4H10O
57
What is the nucleophile in the reaction to form 1-bromobutane?
Butan-1-ol
58
What is produced alongside 1-bromobutane in the reaction?
Water, H2O
59
What technique is used to produce hydrogen bromide within the reaction mixture?
In situ
60
What is added to produce hydrogen bromide in the reaction mixture?
Concentrated sulfuric acid
61
What is the reaction between sodium bromide and sulfuric acid?
NaBr + H2SO4 → NaHSO4 + HBr
62
How is concentrated sulfuric acid added to the reaction mixture?
One drop at a time using a dropping funnel
63
What is the purpose of refluxing the reaction mixture?
To increase the amount of product formed
64
What does reflux describe in a chemical reaction?
Continuous boiling and condensing of a reaction mixture
65
What equipment is used to facilitate refluxing?
A round-bottom flask fitted with a Liebig condenser
66
What are boiling chips or anti-bumping granules used for?
To ensure smooth boiling during refluxing
67
Fill in the blank: The reaction mixture is refluxed for an extended period to allow the reactants to react at an _______.
elevated temperature
68
What is the first step in extracting 1-bromobutane from the reaction mixture?
The reaction mixture is cooled and the apparatus is set up for distillation.
69
What process is used to separate 1-bromobutane from the mixture?
Distillation
70
What happens during the distillation of the reaction mixture?
The mixture is slowly heated until 1-bromobutane boils, producing vapour that condenses into liquid distillate.
71
What type of distillate is obtained from the distillation process?
Crude distillate
72
What indicates that a substance is pure during distillation?
Pure substances distil over a 1-2 °C temperature range.
73
What is the first step in purifying the crude 1-bromobutane?
Shaking the crude 1-bromobutane with dilute sodium hydrogencarbonate solution in a separating funnel.
74
What do acidic impurities in crude 1-bromobutane react with?
Dilute alkali (sodium hydrogencarbonate solution)
75
What products are formed from the reaction of acidic impurities with dilute alkali?
A salt and carbon dioxide gas
76
How is pressure released in the separating funnel during purification?
By inverting the funnel and using the tap to release pressure at intervals.
77
What happens to the 1-bromobutane in the separating funnel?
It forms a separate organic layer as it is immiscible in water.
78
What is done with the upper aqueous layer after separation?
It is discarded.
79
What is the purpose of shaking the organic layer with distilled water?
To remove salts and other water soluble impurities.
80
What is added to the organic layer to remove traces of water?
A solid drying agent such as anhydrous calcium chloride or anhydrous sodium sulfate.
81
What indicates that the product contains small amounts of water?
The product appears cloudy.
82
What happens to the clarity of the product as the drying agent absorbs water?
It becomes increasingly clear.
83
How is the drying agent removed from the mixture?
By filtering the mixture into a clean round-bottom flask.
84
What is the final step to obtain pure dry 1-bromobutane?
Distilling the product.
85
What is the drying agent when purifying the product
Anhydrous sodium sulfate or anhydrous calcium chloride
86
What is a substitution reaction of halogenoalkanes?
A reaction where a halogen atom (-Cl, -Br, -I) is replaced by an -OH group to give an alcohol.
87
What is a nucleophile?
A molecule or ion that attacks regions of low electron density and has a lone pair of electrons that can form a coordinate bond.
88
Which ions are considered nucleophiles?
* Hydroxide ions (OH-)
* Water (H2O)
* Ammonia (NH3)
* Halide ions (F-, Cl-, Br-, I-)
* Cyanide ion (CN-)
89
What is the result of the nucleophilic substitution of 2-bromopropane?
2-bromopropane is converted into propan-2-ol.
90
What does the term 'leaving group' refer to in a substitution reaction?
The atom or group that is replaced by the nucleophile in a reaction.
91
What is the purpose of heating under reflux with sodium or potassium hydroxide in a reaction?
To heat with a condenser placed vertically in the flask to prevent loss of volatile substances.
92
Fill in the blank: The aqueous layer is _______ dense.
less
93
Fill in the blank: The organic layer is _______ dense.
more
94
What does the term 'spectator nucleophile' refer to?
It refers to a nucleophile that does not participate directly in the reaction but is present.
95
In the reaction CH3CHCH3 + NaBr + OH-, what is the leaving group?
Br
96
True or False: The carbon chain changes when a halogen is substituted with a hydroxyl group.
False
97
What is the typical solvent mixture used in reactions involving halogenoalkanes?
A 50/50 mixture of ethanol and water
## Footnote
This mixture is effective because it allows for the dissolution of various compounds.
98
Why is water alone not suitable as a solvent for halogenoalkanes?
Halogenoalkanes are insoluble in water, leading to non-mixing layers
## Footnote
This prevents the reaction from occurring effectively.
99
What product is formed when a halogenoalkane is refluxed with concentrated ammonia?
The corresponding amine
## Footnote
This reaction is an example of nucleophilic substitution.
100
What type of reaction occurs when ammonia replaces halogen in a halogenoalkane?
Nucleophilic substitution
## Footnote
The ammonia uses its lone pair of electrons to form a bond with carbon.
101
What is produced alongside the amine when a halogenoalkane reacts with ammonia?
HBr
## Footnote
HBr subsequently reacts with another ammonia molecule to form ammonium bromide.
102
What is the formula for ammonium bromide?
NH4Br
## Footnote
This compound is formed during the reaction of halogenoalkanes with ammonia.
103
What happens when a halogenoalkane is refluxed with sodium cyanide?
The halogen is replaced by a cyano (-CN) group, forming a nitrile
## Footnote
This reaction results in the production of a nitrile compound.
104
What group is introduced into the compound when a halogenoalkane reacts with cyanide ions?
Cyano (-CN) group
## Footnote
This modifies the halogenoalkane into a nitrile.
105
What is the resulting compound when 1-bromopropane reacts with ammonia?
1-aminopropane
## Footnote
This product is an example of a primary amine.
106
Fill in the blank: The reaction of a halogenoalkane with ammonia results in the formation of _______.
an amine
107
True or False: The reaction between a halogenoalkane and ammonia is a type of electrophilic substitution.
False
## Footnote
It is actually a nucleophilic substitution reaction.
108
What does the cyanide ion (CN:) do in nucleophilic substitution?
Displaces the halogen by using a lone pair to form a coordinate bond with carbon.
## Footnote
This reaction results in the formation of butanenitrile.
109
What is the structure of 1-bromopropane?
CH₃CH₂CH₂Br
## Footnote
It is a primary halogenoalkane.
110
What type of mechanism occurs when nucleophilic substitution happens at a primary halogenoalkane like 1-bromobutane?
SN2 mechanism
## Footnote
This mechanism occurs in a single step.
111
What happens when the hydroxide ion approaches the halogenoalkane in an SN2 reaction?
It uses a lone pair to begin forming a coordinate bond with the electron-deficient carbon.
## Footnote
The carbon is considered electron-deficient due to unequal sharing of electrons in the carbon-halogen bond.
112
What is the nature of the transition state in the SN2 mechanism?
Negatively charged and not a stable substance. Trigonal byprimidal
## Footnote
It cannot be isolated as a compound.
113
What happens to the carbon-halogen bond during the SN2 reaction process?
It begins to break as the coordinate bond forms.
## Footnote
This process leads to the production of a bromide ion.
114
What is the rate equation for the SN2 reaction?
Rate = k[halogenoalkane][nucleophile]
## Footnote
The rate depends on the concentrations of both the halogenoalkane and the nucleophile.
115
Fill in the blank: An ion or molecule with a lone pair of electrons that acts in nucleophilic substitution is called a _______.
Nucleophile
## Footnote
Nucleophiles are key players in SN2 reactions.
116
What is the first step in the SN1 mechanism for tertiary halogenoalkanes?
Heterolytic fission of the carbon halogen bond to produce a tertiary carbocation
## Footnote
This step involves breaking the C-Br bond.
117
What does the hydroxide ion act as in the SN1 mechanism?
A nucleophile
## Footnote
It forms a coordinate bond with the electron-deficient carbon in the carbocation.
118
What is produced in the first step of the SN1 mechanism?
A tertiary carbocation
## Footnote
This carbocation is formed after the fission of the C-Br bond.
119
What is the rate law for the reaction of tertiary halogenoalkanes in SN1 mechanism?
Rate = k[halogenoalkane]
## Footnote
The rate depends only on the concentration of the halogenoalkane.
120
Fill in the blank: The second step of the SN1 mechanism involves hydroxide ion forming a _______ bond with the tertiary carbon.
coordinate
## Footnote
This bond is formed with the electron-deficient carbon in the carbocation.
121
What type of carbon does nucleophilic substitution occur at in the SN1 mechanism?
Tertiary carbon
## Footnote
This is in contrast to primary or secondary carbons.
122
What is the effect of steric hindrance in the SN1 mechanism?
It influences the reactivity of the halogenoalkane
## Footnote
Tertiary halogenoalkanes are more reactive due to less steric hindrance.
123
True or False: The reaction of tertiary halogenoalkanes with hydroxide ions occurs in a single step.
False
## Footnote
The reaction occurs in two steps as part of the SN1 mechanism.
124
What does hydrolysis describe?
A reaction in which bonds are broken as the result of a compound reacting with water
## Footnote
Hydrolysis is a key process in various chemical reactions, including the conversion of halogenoalkanes to alcohols.
125
What is formed when a primary halogenoalkane undergoes hydrolysis with water?
An alcohol
## Footnote
Example: CH₃CH₂CH₂CH₂Br + H₂O → CH₃CH₂CH₂CHOH + HBr
126
What type of reaction is the hydrolysis of halogenoalkanes?
Nucleophilic substitution
## Footnote
This is because water forms a coordinate bond with the electron-deficient carbon in the carbon-halogen bond.
127
Which ion is a better nucleophile than water in hydrolysis reactions?
Hydroxide ion
## Footnote
Hydroxide ions accelerate the hydrolysis of halogenoalkanes compared to water.
128
What is the term for the reaction between a halogenoalkane and dilute alkali to produce an alcohol?
Alkaline hydrolysis
## Footnote
This reaction is faster than hydrolysis with water due to the stronger nucleophilic nature of hydroxide ions.
129
Fill in the blank: The hydrolysis of CH₃CH₂CH₂CH₂Br with OH⁻ produces _______.
CH₃CH₂CH₂CHOH + Br
## Footnote
This demonstrates alkaline hydrolysis of a primary halogenoalkane.
130
What factor affects the rate of hydrolysis related to electronegativity?
Polarity
## Footnote
Electronegativity of the halogens decreases as you go down group 7.
131
Which bond is more polar: C - Cl, C - Br, or C - I?
C - Cl
## Footnote
The order of polarity is C - Cl > C - Br > C - I.
132
How does the polarity of the C - Cl bond affect its reactivity?
The &+ carbon in the C - Cl bond attracts nucleophiles more readily
## Footnote
This results in the fastest reaction among the halogenoalkanes.
133
What is the bond enthalpy for C - Cl?
340 KJ mol*
## Footnote
This value indicates the strength of the bond and relates to reactivity.
134
What is the bond enthalpy for C - Br?
280 KJ mol**
## Footnote
This value is lower than that of C - Cl, indicating less bond strength.
135
What is the relationship between bond energy and reactivity of halogenoalkanes?
Higher bond energy indicates lower reactivity
## Footnote
Lower bond energy means the bond is easier to break, leading to higher reactivity.
136
Fill in the blank: The C - I bond is the least _____ of the three halogenoalkanes.
polar
## Footnote
The order of polarity is C - Cl > C - Br > C - I.
137
What is the bond enthalpy of E(C - l)?
240 KJ mol-1
138
Which halogenoalkane bond is the weakest?
C - I bond
139
What is the significance of bond enthalpy in hydrolysis compared to polarity?
Bond enthalpy is more important than polarity
140
List the order of hydrolysis rate from slowest to fastest.
* 1-fluorobutane
* 1-chlorobutane
* 1-bromobutane
* 1-iodobutane
141
What ions are produced during the hydrolysis of a halogenoalkane?
Halide ions
142
What happens when halide ions are added to silver nitrate solution?
They form a precipitate of the corresponding silver halide
143
Write the general reaction for the hydrolysis of a halogenoalkane.
R-X + H2O → R-OH + H+ + X-
144
What does X represent in the hydrolysis reaction of a halogenoalkane?
Cl, Br, I
145
What is formed when silver ions react with halide ions?
AgX precipitate
146
Fill in the blank: The bond that breaks most readily in hydrolysis will give the ______ reaction.
fastest
147
How can the rate of hydrolysis of a carbon-halogen bond be calculated?
Rate of hydrolysis = 1/Time for precipitate to form
## Footnote
This method involves measuring the time it takes for silver halide precipitate to form.
148
What is the order of precipitate formation during the hydrolysis of 1-chlorobutane, 1-bromobutane, and 1-iodobutane?
The order is:
* AgI (yellow)
* AgBr (cream)
* AgCl (white)
## Footnote
This order indicates that the rate of hydrolysis increases as the carbon-halogen bond becomes weaker.
149
Which carbon-halogen compound has the strongest bond?
1-fluorobutane
## Footnote
1-fluorobutane has the strongest carbon-halogen bond among the compounds listed.
150
Which carbon-halogen compound has the weakest bond?
1-iodobutane
## Footnote
1-iodobutane has the weakest carbon-halogen bond among the compounds listed.
151
What is the fastest carbon-halogen compound in terms of hydrolysis rate?
1-iodobutane
## Footnote
The hydrolysis rate increases as the carbon-halogen bond weakens down the group.
152
What occurs when bromoethane is refluxed with ethanolic potassium hydroxide?
Elimination of hydrogen bromide (HBr)
## Footnote
This reaction results in the formation of an alkene and water.
153
What is ethanolic potassium hydroxide?
A solution of potassium hydroxide dissolved in ethanol
## Footnote
The term 'ethanolic' indicates that ethanol is the solvent used in the solution.
154
What type of reaction involves the loss of a small molecule from a larger molecule?
Elimination reactions
## Footnote
In the context of halogenoalkanes, these reactions involve the removal of HBr and formation of alkenes.
155
What occurs when a halogenoalkane is refluxed with an ethanolic solution of sodium or potassium hydroxide?
Elimination of the corresponding hydrogen halide to form a C=C bond in the product.
156
What is the role of OH in ethanol during the elimination reaction?
Acts as a base to facilitate the elimination process.
157
What is produced as a result of the elimination reaction of 2-bromobutane with ethanolic potassium hydroxide?
A mixture of but-1-ene and but-2-ene.
158
What is the formula for 2-bromobutane?
C4H9Br.
159
What are the products formed by the elimination of hydrogen bromide from 2-bromobutane?
* But-1-ene
* But-2-ene
160
Who developed the non-toxic refrigerant Freon?
Thomas Midgley.
161
What were the gases used as refrigerants before CFCs?
* Ammonia
* Chloromethane
* Sulphur dioxide
162
What is one major issue with CFCs?
They have a devastating effect on the ozone layer.
163
How do CFCs affect the ozone layer?
CFCs absorb UV light and form chlorine radicals that break down ozone.
164
What is the consequence of UV light breaking the C-Cl bond in CFCs?
It releases chlorine radicals.
165
Fill in the blank: CFCs are used in refrigeration and _______.
aerosol propellants.
166
What did Thomas Midgley famously demonstrate to show the non-toxic nature of Freon?
Inhaling the gas and extinguishing a flame by slowly exhaling over it.
167
What is the chemical formula for Freon?
CCl2F2.
168
True or False: CFCs are harmful to human health.
False; they are non-toxic.
169
What are the two stages involved in the breakdown of ozone by CFCs?
* Initiation
* Propagation
170
