Alkyl Halides

• Alkyl halides, also known as haloalkanes or halogenoalkanes, are organic compounds containing one or more halogen atoms (fluorine, chlorine, bromine, or iodine) bonded to carbon atoms within an alkyl group.

Types and Classification

• Alkyl halides can be classified based on two main criteria: the number of halogen atoms in the compound and the type of carbon atom to which the halogen is bonded.

1. Based on the Number of Halogen Atoms:

   1. Monohaloalkanes: Contain one halogen atom. Example: CH3Cl (Methyl Chloride)
   2. Dihaloalkanes: Contain two halogen atoms. Example: CH2Cl2 (Methylene Chloride)
   3. Trihaloalkanes: Contain three halogen atoms. Example: CHCl3 (Chloroform)
   4. Polyhaloalkanes: Contain four or more halogen atoms. Example: CCl4 (Carbon Tetrachloride)

2. Based on the Type of Carbon Atom:

   1. Primary (1°) Alkyl Halides: The halogen is bonded to a primary carbon atom. Example: CH3Cl (Methyl Chloride)
   2. Secondary (2°) Alkyl Halides: The halogen is bonded to a secondary carbon atom. Example: CH3CHClCH3 (Isopropyl Chloride)
   3. Tertiary (3°) Alkyl Halides: The halogen is bonded to a tertiary carbon atom. Example: (CH3)3CCl (tert-Butyl Chloride)

Nomenclature

• The IUPAC nomenclature for alkyl halides follows a straightforward approach:
  1. Chain Selection: Identify the longest carbon chain connected to the halogen.
  2. Numbering: Number the carbon atoms starting from the end nearest to the halogen.
  3. Naming: Combine the locant (position number), the halogen prefix (fluoro, chloro, bromo, or iodo), and the base name of the alkane.

Physical Properties

1. Boiling and Melting Points: Higher than alkanes of similar molecular weight due to the polar carbon-halogen bond, increasing with halogen size.
2. Solubility: Insoluble in water but soluble in organic solvents (e.g., chloroform, ether, alcohols).

Chemical Properties

1. Nucleophilic Substitution: Subject to SN1 and SN2 mechanisms, where the halogen is replaced by a nucleophile.
2. Elimination Reactions: Can form alkenes through E1 or E2 mechanisms by removing a halogen and a hydrogen from adjacent carbons.
3. Reactivity with Metals: React with metals (like magnesium) to form organometallic compounds (e.g., Grignard reagents).

Applications of Alkyl Halides

1. Solvents: Used as solvents in chemical reactions, such as chloroform and methylene chloride.
2. Refrigerants: Some alkyl halides, like CFCs and HFCs, have been used as refrigerants (now restricted due to environmental concerns).
3. Pharmaceuticals: Serve as intermediates in the synthesis of pharmaceuticals and agrochemicals.
4. Polymers: Vinyl chloride is used in the production of polymers like PVC.

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