A haloalkane is an alkane in which one or more hydrogen atoms have been replaced by a halogen atom , creating a polar C-X bond .

True or False? The C-F bond has the highest bond enthalpy of all carbon-halogen bonds.

True. Bond enthalpy decreases in the order C-F > C-Cl > C-Br > C-I, so fluoroalkanes are the least reactive haloalkanes.

Why is ethanol added when reacting a haloalkane with aqueous sodium hydroxide?

Haloalkanes are insoluble in water , so ethanol is used as a co-solvent to allow the organic and aqueous layers to mix and the reaction to proceed throughout the solution.

A chloroalkane gives a .......... precipitate. A bromoalkane gives a .......... precipitate. An iodoalkane gives a .......... precipitate.

A chloroalkane gives a white precipitate. A bromoalkane gives a cream precipitate. An iodoalkane gives a yellow precipitate.

State the order of reactivity of haloalkanes in nucleophilic substitution, from fastest to slowest.

Iodoalkane > bromoalkane > chloroalkane > fluoroalkane, because bond enthalpy increases in this order and a weaker C-X bond is broken more easily.

What two types of reaction do haloalkanes undergo due to the polar C-X bond?

Nucleophilic substitution reactions (replacing X with another group) Elimination reactions (removing HX to form an alkene)

True or False? The carbon atom in a C-X bond carries a partial positive charge.

True. Halogens are more electronegative than carbon, so they pull electron density towards themselves, leaving the carbon with a partial positive charge (δ+).

A nucleophile is an electron-rich species that can donate a pair of electrons to an electron-deficient carbon atom.

The three common nucleophiles used are OH - , .......... and .......... . They replace the .......... atom in the haloalkane.

The three common nucleophiles used are OH - , CN - and NH 3 . They replace the halogen atom in a haloalkane.

True or False? The hydroxide ion is a stronger nucleophile than water.

True. OH - carries a full negative charge , giving it greater electron density to donate than water, which only has a partial negative charge on oxygen.

What product is formed when a haloalkane reacts with aqueous OH - ?

An alcohol is formed as the hydroxide ion replaces the halogen in a nucleophilic substitution reaction.

What product is formed when a haloalkane reacts with the nucleophile CN - ?

A nitrile is formed as the cyanide ion replaces the halogen , increasing the carbon chain length by one.

True or False? In nucleophilic substitution, the nucleophile attacks the carbon carrying a partial negative charge.

False. The nucleophile attacks the carbon carrying a partial positive charge (δ+), which arises because the electronegative halogen pulls electron density away from the carbon.

What product is formed when a haloalkane reacts with excess NH 3 ?

An amine is formed as the ammonia acts as a nucleophile, donating its lone pair to the δ+ carbon and displacing the halide ion.

Define hydrolysis (of a haloalkane)

A hydrolysis is a reaction in which a C-X bond is broken by a nucleophile (OH - or water), replacing the halogen with an -OH group to form an alcohol.

True or False? Iodoalkanes hydrolyse faster than chloroalkanes.

True. The C-I bond has a lower bond enthalpy than the C-Cl bond, so it is broken more easily, giving iodoalkanes a faster rate of hydrolysis.

Why do fluoroalkanes not undergo hydrolysis under normal conditions?

The C-F bond has the highest bond enthalpy of all carbon-halogen bonds and is therefore too strong to be broken under normal reaction conditions.

Acidified silver nitrate is used so that .......... ions are detected as they form. The .......... precipitate forms fastest, showing iodoalkanes hydrolyse most rapidly. The .......... precipitate forms slowest.

Acidified silver nitrate is used so that halide ions are detected as they form. The yellow precipitate (silver iodide) forms fastest, showing iodoalkanes hydrolyse most rapidly. The white precipitate (silver chloride) forms slowest.

State the order of hydrolysis rate for haloalkanes, from fastest to slowest, and explain the trend.

R-I > R-Br > R-Cl > R-F, because bond enthalpy increases in this order and a lower bond enthalpy means the C-X bond is more easily broken.

True or False? The rate of hydrolysis of haloalkanes is determined by bond polarity.

False. The rate is determined by bond enthalpy (bond strength), not polarity — a weaker C-X bond is broken more readily, giving a faster rate of hydrolysis.

Define CFC (chlorofluorocarbon)

A CFC (chlorofluorocarbon) is an organohalogen compound containing only carbon , chlorine and fluorine atoms, formerly used as refrigerants and aerosol propellants.

How is a chlorine radical formed from a CFC in the upper atmosphere?

CFCs absorb UV radiation in the upper atmosphere, which breaks the C-Cl bond homolytically to release a chlorine radical (Cl•).

Complete the two propagation steps for ozone destruction by chlorine radicals. Propagation 1: Cl• + O 3 → .......... + O 2 Propagation 2: .......... + O → Cl• + O 2

Propagation 1: Cl• + O 3 → ClO• + O 2 Propagation 2: ClO• + O → Cl• + O 2

True or False? HFCs (hydrofluorocarbons) are used as safer alternatives to CFCs because they do not contain chlorine.

True. HFCs contain only carbon, hydrogen and fluorine, so they cannot release chlorine radicals and therefore do not contribute to ozone depletion .

Why is a single chlorine radical able to destroy thousands of ozone molecules?

Cl• acts as a catalyst — it is regenerated at the end of each propagation cycle, so it can continue to react with further O 3 molecules repeatedly.

State the overall equation for the catalytic destruction of ozone by chlorine radicals.

O 3 + O → 2O 2 The Cl• radical is not consumed overall, confirming its role as a catalyst in the chain reaction.

True or False? Nitrogen monoxide radicals can also catalyse the breakdown of ozone in the stratosphere.

True. NO• reacts with O 3 to form NO 2 •, which is then converted back to NO•, making it a catalyst for ozone destruction in the same way as Cl•.

A LevelChemistryOCRFlashcards4. Core Organic ChemistryHaloalkanes

Haloalkanes (OCR A Level Chemistry A): Flashcards

Exam code: H432

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Cards in this collection (27)

Define haloalkane
A haloalkane is an alkane in which one or more hydrogen atoms have been replaced by a halogen atom, creating a polar C-X bond.
True or False?
The C-F bond has the highest bond enthalpy of all carbon-halogen bonds.
True.
Bond enthalpy decreases in the order C-F > C-Cl > C-Br > C-I, so fluoroalkanes are the least reactive haloalkanes.
Why is ethanol added when reacting a haloalkane with aqueous sodium hydroxide?
Haloalkanes are insoluble in water, so ethanol is used as a co-solvent to allow the organic and aqueous layers to mix and the reaction to proceed throughout the solution.
A chloroalkane gives a .......... precipitate.
A bromoalkane gives a .......... precipitate.
An iodoalkane gives a .......... precipitate.
A chloroalkane gives a white precipitate.
A bromoalkane gives a cream precipitate.
An iodoalkane gives a yellow precipitate.
State the order of reactivity of haloalkanes in nucleophilic substitution, from fastest to slowest.
Iodoalkane > bromoalkane > chloroalkane > fluoroalkane, because bond enthalpy increases in this order and a weaker C-X bond is broken more easily.
What two types of reaction do haloalkanes undergo due to the polar C-X bond?
1. Nucleophilic substitution reactions (replacing X with another group)
2. Elimination reactions (removing HX to form an alkene)
True or False?
The carbon atom in a C-X bond carries a partial positive charge.
True.
Halogens are more electronegative than carbon, so they pull electron density towards themselves, leaving the carbon with a partial positive charge (δ+).
Define nucleophile
A nucleophile is an electron-rich species that can donate a pair of electrons to an electron-deficient carbon atom.
The three common nucleophiles used are OH^-, .......... and ...........
They replace the .......... atom in the haloalkane.
The three common nucleophiles used are OH^-, CN^- and NH₃.
They replace the halogen atom in a haloalkane.
True or False?
The hydroxide ion is a stronger nucleophile than water.
True.
OH^- carries a full negative charge, giving it greater electron density to donate than water, which only has a partial negative charge on oxygen.
What product is formed when a haloalkane reacts with aqueous OH^-?
An alcohol is formed as the hydroxide ion replaces the halogen in a nucleophilic substitution reaction.
What product is formed when a haloalkane reacts with the nucleophile CN^-?
A nitrile is formed as the cyanide ion replaces the halogen, increasing the carbon chain length by one.
True or False?
In nucleophilic substitution, the nucleophile attacks the carbon carrying a partial negative charge.
False.
The nucleophile attacks the carbon carrying a partial positive charge (δ+), which arises because the electronegative halogen pulls electron density away from the carbon.
What product is formed when a haloalkane reacts with excess NH₃?
An amine is formed as the ammonia acts as a nucleophile, donating its lone pair to the δ+ carbon and displacing the halide ion.
Define hydrolysis (of a haloalkane)
A hydrolysis is a reaction in which a C-X bond is broken by a nucleophile (OH^- or water), replacing the halogen with an -OH group to form an alcohol.
True or False?
Iodoalkanes hydrolyse faster than chloroalkanes.
True.
The C-I bond has a lower bond enthalpy than the C-Cl bond, so it is broken more easily, giving iodoalkanes a faster rate of hydrolysis.
Why do fluoroalkanes not undergo hydrolysis under normal conditions?
The C-F bond has the highest bond enthalpy of all carbon-halogen bonds and is therefore too strong to be broken under normal reaction conditions.
Acidified silver nitrate is used so that .......... ions are detected as they form.
The .......... precipitate forms fastest, showing iodoalkanes hydrolyse most rapidly.
The .......... precipitate forms slowest.
Acidified silver nitrate is used so that halide ions are detected as they form.
The yellow precipitate (silver iodide) forms fastest, showing iodoalkanes hydrolyse most rapidly.
The white precipitate (silver chloride) forms slowest.
State the order of hydrolysis rate for haloalkanes, from fastest to slowest, and explain the trend.
R-I > R-Br > R-Cl > R-F, because bond enthalpy increases in this order and a lower bond enthalpy means the C-X bond is more easily broken.
True or False?
The rate of hydrolysis of haloalkanes is determined by bond polarity.
False.
The rate is determined by bond enthalpy (bond strength), not polarity — a weaker C-X bond is broken more readily, giving a faster rate of hydrolysis.
Define CFC (chlorofluorocarbon)
A CFC (chlorofluorocarbon) is an organohalogen compound containing only carbon, chlorine and fluorine atoms, formerly used as refrigerants and aerosol propellants.
How is a chlorine radical formed from a CFC in the upper atmosphere?
CFCs absorb UV radiation in the upper atmosphere, which breaks the C-Cl bond homolytically to release a chlorine radical (Cl•).
Complete the two propagation steps for ozone destruction by chlorine radicals.
Propagation 1: Cl• + O₃ → .......... + O₂
Propagation 2: .......... + O → Cl• + O₂
Propagation 1: Cl• + O₃ → ClO• + O₂
Propagation 2: ClO• + O → Cl• + O₂
True or False?
HFCs (hydrofluorocarbons) are used as safer alternatives to CFCs because they do not contain chlorine.
True.
HFCs contain only carbon, hydrogen and fluorine, so they cannot release chlorine radicals and therefore do not contribute to ozone depletion.
Why is a single chlorine radical able to destroy thousands of ozone molecules?
Cl• acts as a catalyst — it is regenerated at the end of each propagation cycle, so it can continue to react with further O₃ molecules repeatedly.
State the overall equation for the catalytic destruction of ozone by chlorine radicals.
O₃ + O → 2O₂
The Cl• radical is not consumed overall, confirming its role as a catalyst in the chain reaction.
True or False?
Nitrogen monoxide radicals can also catalyse the breakdown of ozone in the stratosphere.
True.
NO• reacts with O₃ to form NO₂•, which is then converted back to NO•, making it a catalyst for ozone destruction in the same way as Cl•.

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