Haloalkanes and Haloarenes - Nomenclature

• Introduction
• Classification of haloalkanes
• Naming haloalkanes
• Suffixes used for haloalkanes
• Examples of naming haloalkanes:
  • Chloroethane (C2H5Cl)
  • Bromobutane (C4H9Br)
• Classification of haloarenes
• Naming haloarenes
• Suffixes used for haloarenes
• Examples of naming haloarenes:
  • Chlorobenzene (C6H5Cl)

11. Classification of Haloalkanes:

• Primary haloalkanes: The halogen atom is attached to a carbon atom that is bonded to only one other carbon atom.
• Secondary haloalkanes: The halogen atom is attached to a carbon atom that is bonded to two other carbon atoms.
• Tertiary haloalkanes: The halogen atom is attached to a carbon atom that is bonded to three other carbon atoms.

12. Naming Haloalkanes:

• Step 1: Find the longest carbon chain in the molecule.
• Step 2: Number the carbon atoms in the chain, starting from the end closest to the halogen atom.
• Step 3: Name the substituents attached to the chain, using prefixes like methyl, ethyl, etc.
• Step 4: Determine the position of the halogen atom.
• Step 5: Write the name of the haloalkane by combining the substituent names and the halogen name.

13. Suffixes used for Haloalkanes:

• Fluoro-
• Chloro-
• Bromo-
• Iodo-

14. Examples of Naming Haloalkanes:

• Example 1: 1-Bromobutane (C4H9Br)
• Example 2: 2-Chloro-2-methylpropane (C4H9Cl)

15. Classification of Haloarenes:

• Mono-haloarenes: Only one halogen atom is attached to the aromatic ring.
• Di-haloarenes: Two halogen atoms are attached to the aromatic ring.
• Poly-haloarenes: More than two halogen atoms are attached to the aromatic ring.

16. Naming Haloarenes:

• Step 1: Name the parent aromatic hydrocarbon by using the IUPAC rules.
• Step 2: Number the carbon atoms in the ring, starting from the position of the first halogen atom.
• Step 3: Name the halogen substituents, using prefixes like chloro, bromo, etc.
• Step 4: Write the substituent names in alphabetical order.

17. Suffixes used for Haloarenes:

• Fluoro-
• Chloro-
• Bromo-
• Iodo-

18. Examples of Naming Haloarenes:

• Example 1: 1-Chlorobenzene (C6H5Cl)
• Example 2: 2,4-Dibromobenzene (C6H4Br2)

19. Importance of Haloalkanes and Haloarenes:

• Used as intermediates in the synthesis of various organic compounds.
• Used in the pharmaceutical industry for the production of medicines.
• Used as solvents in various chemical reactions.
• Used as pesticides and flame retardants.

20. Key Takeaways:

• Haloalkanes are classified based on the number of carbon atoms bonded to the carbon atom with the halogen atom.
• Haloalkanes are named by identifying the longest carbon chain, numbering the carbon atoms, and naming the substituents and halogen.
• Haloarenes are named by identifying the parent aromatic hydrocarbon, numbering the carbon atoms, and naming the halogen substituents.
• Haloalkanes and haloarenes have various applications in industries such as pharmaceuticals and agriculture.

21. Reactions of Haloalkanes:

• Substitution reactions:
  • Nucleophilic substitution reaction: Nucleophile replaces the halogen atom.
  • Example: SN2 reaction of bromoethane with hydroxide ion.
  • Radical substitution reaction: A radical replaces the halogen atom.
  • Example: Chlorination of methane with chlorine.
• Elimination reactions:
  • Dehydrohalogenation reaction: Alkene is formed by the removal of a hydrogen halide.
  • Example: Dehydrohalogenation of 2-chloro-2-methylpropane.
• Addition reactions:
  • Hydrogenation reaction: Addition of hydrogen to form alkane.
  • Example: Hydrogenation of 1-bromo-1-methylcyclohexane.
• Rearrangement reactions:
  • Solvolysis reaction: Substitution reaction accompanied by a rearrangement.
  • Example: Solvolysis of 2-chloro-2-methylbutane.

22. Reactivity of Haloalkanes:

• The reactivity of haloalkanes depends on:
  • The nature of the halogen atom.
  • The nature of the carbon-halogen bond.
  • The presence of other functional groups.
• The reactivity decreases in the order:
  • Fluoroalkanes > Chloroalkanes > Bromoalkanes > Iodoalkanes.
• Aromatic haloalkanes are generally less reactive compared to aliphatic haloalkanes.
• The carbon-fluorine bond is the strongest and least reactive among carbon-halogen bonds.
• The carbon-iodine bond is the weakest and most reactive among carbon-halogen bonds.

23. SN1 Mechanism:

• SN1 (substitution nucleophilic unimolecular) mechanism involves two steps:
  1. Formation of a carbocation intermediate by the departure of the halide ion.
  2. Nucleophilic attack on the carbocation by the nucleophile.
• SN1 reactions proceed through a transition state with a high-energy carbocation intermediate.
• SN1 reactions are favored by:
  • Polar protic solvents.
  • Tertiary haloalkanes.
  • Weak nucleophiles.
• Example: SN1 reaction of tert-butyl chloride with water.

24. SN2 Mechanism:

• SN2 (substitution nucleophilic bimolecular) mechanism involves a single step:
  • Nucleophilic attack on the carbon atom and departure of the halide ion occur simultaneously.
• SN2 reactions have a one-step concerted mechanism, with no carbocation intermediate formation.
• SN2 reactions are favored by:
  • Polar aprotic solvents.
  • Primary and secondary haloalkanes.
  • Strong nucleophiles.
• Example: SN2 reaction of chloroethane with hydroxide ion.

25. Elimination Reactions:

• Elimination reactions involve the removal of a molecule (usually a hydrogen halide) to form a double bond.
• E1 (elimination unimolecular) mechanism:
  • Formation of a carbocation intermediate followed by the removal of a hydrogen halide.
• E2 (elimination bimolecular) mechanism:
  • Simultaneous removal of a hydrogen halide by a base as it attacks the carbon atom.
• Example: E2 elimination of 2-bromopropane with sodium ethoxide.

26. Addition Reactions:

• Addition reactions involve the addition of atoms or groups to form a single product.
• Hydrogenation reaction:
  • Addition of hydrogen to a double bond to form an alkane.
  • Example: Hydrogenation of 2-bromo-1-butene.
• Halogenation reaction:
  • Addition of a halogen to an alkene to form a dihaloalkane.
  • Example: Bromination of ethene to form 1,2-dibromoethane.
• Hydration reaction:
  • Addition of water to an alkene to form an alcohol.
  • Example: Hydration of propene to form propanol.

27. Nucleophilic Substitution Reactions of Haloarenes:

• Nucleophilic aromatic substitution (SNAr) reactions involve the substitution of a halogen atom in a haloarene by a nucleophile.
• SNAr reactions proceed through a negatively charged intermediate called the Meisenheimer complex.
• Aromatic nucleophilic substitution (SNAr) reactions can occur via two mechanisms:
  1. Addition-elimination mechanism (benzyne mechanism).
  2. Direct displacement mechanism.
• Example: SNAr reaction of chlorobenzene with sodium hydroxide.

28. Electrophilic Substitution Reactions of Haloarenes:

• Electrophilic aromatic substitution (SEAr) reactions involve the substitution of a proton or an existing substituent in a haloarene by an electrophile.
• SEAr reactions proceed through the formation of a π-complex intermediate.
• Common electrophilic substitution reactions include:
  • Nitration: Introduction of a nitro group (-NO2).
  • Halogenation: Introduction of a halogen atom.
  • Friedel-Crafts alkylation: Introduction of an alkyl group.
  • Friedel-Crafts acylation: Introduction of an acyl group.
• Example: Nitration of bromobenzene to form 4-nitrobromobenzene.

29. Reactivity of Haloarenes:

• The reactivity of haloarenes depends on the nature of the halogen atom and the presence of other functional groups.
• The reactivity increases in the order:
  • Fluoroarenes < Chloroarenes < Bromoarenes < Iodoarenes.
• Aromatic compounds with electron-donating groups are more reactive towards electrophilic substitution reactions.
• Aromatic compounds with electron-withdrawing groups are less reactive towards nucleophilic substitution reactions.

30. Key Takeaways:

• Haloalkanes undergo various reactions, including substitution, elimination, addition, and rearrangement reactions.
• The reactivity of haloalkanes depends on the nature of the halogen atom and the carbon-halogen bond.
• SN1 and SN2 mechanisms describe nucleophilic substitution reactions of haloalkanes.
• E1 and E2 mechanisms are involved in elimination reactions of haloalkanes.
• Haloarenes undergo nucleophilic and electrophilic substitution reactions.
• The reactivity of haloarenes depends on the nature of the halogen atom and the presence of other functional groups.
• Understanding the reactivity of haloalkanes and haloarenes is essential in organic synthesis and pharmaceutical development.