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Questions and Answers
What is the definition of a radical?
What is the definition of a radical?
What type of bond cleavage results in two radicals with one unpaired electron each?
What type of bond cleavage results in two radicals with one unpaired electron each?
What is the result of heterolytic bond cleavage?
What is the result of heterolytic bond cleavage?
What is the first step in a free radical reaction?
What is the first step in a free radical reaction?
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What is the result of the reaction between methane and chlorine gas?
What is the result of the reaction between methane and chlorine gas?
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Why is chlorine highly reactive and non-selective?
Why is chlorine highly reactive and non-selective?
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What happens as the reactivity of halogens decreases?
What happens as the reactivity of halogens decreases?
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Why is fluorine not used in reactions?
Why is fluorine not used in reactions?
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What type of bond cleavage results in the formation of ions with opposite charges?
What type of bond cleavage results in the formation of ions with opposite charges?
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What is the role of initiation in a free radical reaction?
What is the role of initiation in a free radical reaction?
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What is the product of the reaction between methane and chlorine gas?
What is the product of the reaction between methane and chlorine gas?
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Why is bromine less reactive than chlorine?
Why is bromine less reactive than chlorine?
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What is the trend in the reactivity of halogens?
What is the trend in the reactivity of halogens?
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What is the result of the propagation step in a free radical reaction?
What is the result of the propagation step in a free radical reaction?
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Why is iodine not reactive enough to replace hydrogen atoms?
Why is iodine not reactive enough to replace hydrogen atoms?
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What is the trend in the selectivity of halogens?
What is the trend in the selectivity of halogens?
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Study Notes
Radicals and Free Radical Reactions
- A radical is an atom or species with an unpaired number of electrons, which can have an odd number of electrons.
- Radicals are formed through two types of bond cleavages: homolytic and heterolytic.
Homolytic Bond Cleavage
- A bond breaks equally, resulting in two radicals with one unpaired electron each.
- Example: Bromine (Br2) breaks down into two bromine radicals (Br·) under heat or UV light.
Heterolytic Bond Cleavage
- A bond breaks unequally, resulting in two ions with opposite charges.
- Example: Carbon-bromine bond breaks, with bromine pulling the electrons towards itself, forming a carbocation and a bromide ion.
- Carbon-hydrogen bond breaks, with carbon pulling the electrons towards itself, forming a carbanion and a hydrogen ion.
Free Radical Reactions
- Initiation: A neutral molecule turns into two radicals.
- Propagation: One radical reacts with a molecule to form another radical.
- Termination: Two radicals react to form a molecule.
Chlorination of Methane
- Methane (CH4) reacts with chlorine gas (Cl2) to form methyl chloride (CH3Cl) and hydrochloric acid (HCl).
- Mechanism:
- Initiation: Cl2 breaks down into two chlorine radicals (Cl·) under heat or UV light.
- Propagation: Cl· reacts with methane to form a methyl radical (CH3·) and HCl.
- Propagation: Cl· reacts with CH3· to form CH3Cl and regenerate Cl·.
Reactivity of Halogens
- Chlorine (Cl2) is highly reactive and non-selective, substituting hydrogen atoms randomly.
- Bromine (Br2) is less reactive and selective, preferring to substitute secondary hydrogens.
- Iodine (I2) is not reactive enough to replace hydrogen atoms.
- Fluorine (F2) is too reactive and dangerous to use.
Selectivity of Halogens
- The reactivity of halogens decreases from top to bottom of the periodic table (F > Cl > Br > I).
- As reactivity decreases, selectivity increases.
- Chlorine is less selective due to small differences in activation energy for abstracting primary, secondary, and tertiary hydrogens.
- Bromine is more selective due to large differences in activation energy for abstracting different hydrogens.
Relative Reactivity Rates
- Chlorine: 5 (tertiary) > 3.8 (secondary) > 1 (primary)
- Bromine: 1600 (tertiary) > 82 (secondary) > 1 (primary)
Radicals and Free Radical Reactions
- Radicals are atoms or species with an unpaired number of electrons, which can have an odd number of electrons.
- Radicals are formed through homolytic and heterolytic bond cleavages.
Homolytic Bond Cleavage
- A bond breaks equally, resulting in two radicals with one unpaired electron each.
- Example: Bromine (Br2) breaks down into two bromine radicals (Br·) under heat or UV light.
Heterolytic Bond Cleavage
- A bond breaks unequally, resulting in two ions with opposite charges.
- Example: Carbon-bromine bond breaks, with bromine pulling the electrons towards itself, forming a carbocation and a bromide ion.
- Example: Carbon-hydrogen bond breaks, with carbon pulling the electrons towards itself, forming a carbanion and a hydrogen ion.
Free Radical Reactions
- Initiation: A neutral molecule turns into two radicals.
- Propagation: One radical reacts with a molecule to form another radical.
- Termination: Two radicals react to form a molecule.
Chlorination of Methane
- Methane (CH4) reacts with chlorine gas (Cl2) to form methyl chloride (CH3Cl) and hydrochloric acid (HCl).
- Mechanism involves initiation, propagation, and termination steps:
- Initiation: Cl2 breaks down into two chlorine radicals (Cl·) under heat or UV light.
- Propagation: Cl· reacts with methane to form a methyl radical (CH3·) and HCl.
- Propagation: Cl· reacts with CH3· to form CH3Cl and regenerate Cl·.
Reactivity of Halogens
- Chlorine (Cl2) is highly reactive and non-selective, substituting hydrogen atoms randomly.
- Bromine (Br2) is less reactive and selective, preferring to substitute secondary hydrogens.
- Iodine (I2) is not reactive enough to replace hydrogen atoms.
- Fluorine (F2) is too reactive and dangerous to use.
Selectivity of Halogens
- The reactivity of halogens decreases from top to bottom of the periodic table (F > Cl > Br > I).
- As reactivity decreases, selectivity increases.
- Chlorine is less selective due to small differences in activation energy for abstracting primary, secondary, and tertiary hydrogens.
- Bromine is more selective due to large differences in activation energy for abstracting different hydrogens.
Relative Reactivity Rates
- Chlorine: 5 (tertiary) > 3.8 (secondary) > 1 (primary)
- Bromine: 1600 (tertiary) > 82 (secondary) > 1 (primary)
Radicals and Free Radical Reactions
- Radicals are atoms or species with an unpaired number of electrons, which can have an odd number of electrons.
- Radicals are formed through homolytic and heterolytic bond cleavages.
Homolytic Bond Cleavage
- A bond breaks equally, resulting in two radicals with one unpaired electron each.
- Example: Bromine (Br2) breaks down into two bromine radicals (Br·) under heat or UV light.
Heterolytic Bond Cleavage
- A bond breaks unequally, resulting in two ions with opposite charges.
- Example: Carbon-bromine bond breaks, with bromine pulling the electrons towards itself, forming a carbocation and a bromide ion.
- Example: Carbon-hydrogen bond breaks, with carbon pulling the electrons towards itself, forming a carbanion and a hydrogen ion.
Free Radical Reactions
- Initiation: A neutral molecule turns into two radicals.
- Propagation: One radical reacts with a molecule to form another radical.
- Termination: Two radicals react to form a molecule.
Chlorination of Methane
- Methane (CH4) reacts with chlorine gas (Cl2) to form methyl chloride (CH3Cl) and hydrochloric acid (HCl).
- Mechanism involves initiation, propagation, and termination steps:
- Initiation: Cl2 breaks down into two chlorine radicals (Cl·) under heat or UV light.
- Propagation: Cl· reacts with methane to form a methyl radical (CH3·) and HCl.
- Propagation: Cl· reacts with CH3· to form CH3Cl and regenerate Cl·.
Reactivity of Halogens
- Chlorine (Cl2) is highly reactive and non-selective, substituting hydrogen atoms randomly.
- Bromine (Br2) is less reactive and selective, preferring to substitute secondary hydrogens.
- Iodine (I2) is not reactive enough to replace hydrogen atoms.
- Fluorine (F2) is too reactive and dangerous to use.
Selectivity of Halogens
- The reactivity of halogens decreases from top to bottom of the periodic table (F > Cl > Br > I).
- As reactivity decreases, selectivity increases.
- Chlorine is less selective due to small differences in activation energy for abstracting primary, secondary, and tertiary hydrogens.
- Bromine is more selective due to large differences in activation energy for abstracting different hydrogens.
Relative Reactivity Rates
- Chlorine: 5 (tertiary) > 3.8 (secondary) > 1 (primary)
- Bromine: 1600 (tertiary) > 82 (secondary) > 1 (primary)
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Description
Understanding radicals and their formation through homolytic and heterolytic bond cleavages. Learn about the properties and examples of radical reactions.
