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Halogen derivatives are compounds where one or more hydrogen atoms of another molecule have been replaced by _________ such as fluorine, chlorine, bromine, iodine, or astatine.
Halogen derivatives are compounds where one or more hydrogen atoms of another molecule have been replaced by _________ such as fluorine, chlorine, bromine, iodine, or astatine.
halogens
Halogen derivatives are formed through various types of _________ reactions.
Halogen derivatives are formed through various types of _________ reactions.
halogenation
Electrophilic aromatic substitution is a method of forming halogen derivatives by interaction with electron-rich _________ systems.
Electrophilic aromatic substitution is a method of forming halogen derivatives by interaction with electron-rich _________ systems.
aromatic
Bromination of benzene proceeds through the reaction between molecular bromine and an aromatic solvent containing concentrated sulfuric acid, resulting in the formation of hydrogen _________ as a byproduct.
Bromination of benzene proceeds through the reaction between molecular bromine and an aromatic solvent containing concentrated sulfuric acid, resulting in the formation of hydrogen _________ as a byproduct.
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The mechanism of electrophilic aromatic substitution typically consists of three steps: formation of an electrophile, electrophilic attack, and _________ (elimination of H⁺).
The mechanism of electrophilic aromatic substitution typically consists of three steps: formation of an electrophile, electrophilic attack, and _________ (elimination of H⁺).
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Activation of the halogen species by Lewis acids creates an electrophile capable of attacking the aromatic system, often in the form of a positively charged _________ ion.
Activation of the halogen species by Lewis acids creates an electrophile capable of attacking the aromatic system, often in the form of a positively charged _________ ion.
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Electrophilic attachment of the positive center onto the aromatic ring, leading to the formation of a sigma bond and temporary loss of aromaticity is a characteristic of ______ reactions.
Electrophilic attachment of the positive center onto the aromatic ring, leading to the formation of a sigma bond and temporary loss of aromaticity is a characteristic of ______ reactions.
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Nucleophilic Aromatic Substitution involves the addition of a negatively charged halogen ion directly to the aromatic compound, replacing an existing ______.
Nucleophilic Aromatic Substitution involves the addition of a negatively charged halogen ion directly to the aromatic compound, replacing an existing ______.
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Commonly used reagents for nucleophilic aromatic substitution include alkali metal halides dissolved in liquid ______.
Commonly used reagents for nucleophilic aromatic substitution include alkali metal halides dissolved in liquid ______.
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The nitration and subsequent lithium bromide reduction of pyrrole leads to 3-______.
The nitration and subsequent lithium bromide reduction of pyrrole leads to 3-______.
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Aliphatic compounds can form halogen derivatives using direct halogenation employing elemental halogens or halogen oxides such as chlorine ______.
Aliphatic compounds can form halogen derivatives using direct halogenation employing elemental halogens or halogen oxides such as chlorine ______.
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Free radical halogenation procedures involve redox initiation and reactive intermediates called radical ______.
Free radical halogenation procedures involve redox initiation and reactive intermediates called radical ______.
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Study Notes
Halogen Derivatives and their Formation via Halogenation Reactions
Halogen derivatives are compounds where one or more hydrogen atoms of another molecule have been replaced by halogens such as fluorine (F), chlorine (Cl), bromine (Br), iodine (I), or astatine (At). These substitutions occur through various types of halogenation reactions. In this exploration, we'll delve into these transformations and the common mechanisms behind them.
Electrophilic Aromatic Substitution
One method of forming halogen derivatives involves electrophilic aromatic substitution. This process occurs when halogenating agents like interhalogens (e.g., Cl₂, Br₂) interact with electron-rich aromatic ring systems. For example, bromination of benzene proceeds through the reaction between molecular bromine and an aromatic solvent containing concentrated sulfuric acid (H₂SO₄). Hydrogen bromide is formed as a byproduct during the reaction.
[C_6H_6 + Br_2 \rightarrow C_6H_5Br + HBr]
The mechanism typically consists of three steps: formation of an electrophile, electrophilic attack, and deprotonation (elimination of H⁺):
- Activation of the halogen species by Lewis acids creates an electrophile (like a positively charged halonium ion) capable of attacking the aromatic system: [Br_2 + HSbF_6^- \rightleftharpoons SbF_6^{-} + Br^+]
- Electrophilic attachment of the positive center onto the aromatic ring, leading to the formation of a sigma bond and temporary loss of aromaticity: [C_6H_5^•+Br\rightarrow{C_6H_5Br}^+]
- Deprotonation from an adjacent carbon atom restores the aromatic character: [{C_6H_5Br}^++CH=X\rightarrow{C_6H_5Br}+CHX]
Nucleophilic Aromatic Substitution
In contrast to electrophilic approaches, nucleophilic methods involve the addition of a negatively charged halogen ion (anion) directly to the aromatic compound, replacing an existing proton. Commonly used reagents include alkali metal halides dissolved in liquid ammonia.
For instance, the nitration and subsequent lithium bromide reduction of pyrrole leads to 3-bromopyrrole:
[C_4H_4NH_2 + NO_2^-(in~liquid ~NH_3) → C_4H_3NH^+NO_2 + H_2O] [C_4H_3N^+NO_2 + LiBr → C_4H_3Br + LiNOPhr + H_2O]
Halogenation of Aliphatic Compounds
Aliphatic compounds can also form halogen derivatives using several strategies:
- Direct halogenation employing elemental halogens or halogen oxides such as chlorine dioxide (ClO₂).
- Free radical halogenation procedures involving redox initiation and reactive intermediates called radical cations.
- Solvolytic replacement of existing functional groups like thiols (-SH) by halogens under specific conditions.
These varied processes reveal the tremendous flexibility inherent within halogen chemistry to produce diverse halogenated products. As you explore further, keep in mind the central themes: the versatility of halogenation techniques, the role of transition states and intermediates in these processes, and the impact of experimental factors upon product selectivity.
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Description
Test your knowledge on halogen derivatives and their formation through various halogenation reactions, including electrophilic and nucleophilic aromatic substitutions, as well as halogenation of aliphatic compounds. Explore the mechanisms, reagents, and reaction pathways involved in creating halogenated products.
