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Alkyl Halide Nomenclature

 Alkyl Halide Nomenclature


Nomenclature of alkyl halides, also known as haloalkanes or alkyl halogen compounds, follows a specific set of rules established by the International Union of Pure and Applied Chemistry (IUPAC). These rules help to systematically name these compounds based on their structure. Here's a general guideline for naming alkyl halides:

  • Identify the Parent Chain: Determine the longest continuous carbon chain that includes the carbon atom bonded to the halogen atom (the halogen atom is the substituent in this case). This chain is the parent chain.
  • Numbering the Parent Chain: Number the carbon atoms in the parent chain so that the carbon atom bonded to the halogen (the haloalkane functional group) gets the lowest possible number. Numbering should proceed in the direction that gives the lowest numbers to the substituents bonded to the carbon atoms.
  • Name the Halogen Substituent: Use the prefix for the halogen followed by the position number where it's attached to the parent chain. The prefixes for common halogens are:
  • Fluoro- for fluorine (F)
  • Chloro- for chlorine (Cl)
  • Bromo- for bromine (Br)
  • Iodo- for iodine (I)
  • Name the Alkyl Groups: If there are alkyl groups attached to the parent chain, name them as substituents using the alkyl group's name followed by the position number where it's attached to the parent chain. Alphabetical order is used to arrange the substituent names.
  • Indicate the Number of Halogen Atoms: If the halogen atom is part of a diatomic molecule (e.g., Cl2 or Br2), you can use prefixes like "di" for two, "tri" for three, etc., to indicate the number of halogen atoms. This is necessary when there is more than one halogen atom attached to a carbon.
  • Combine the Names: Combine all the substituent names (halogens and alkyl groups) along with the parent chain name. Separate them with hyphens, and use commas to separate position numbers when necessary.
  • Use Numerical Prefixes: When there is more than one identical substituent, use numerical prefixes like di-, tri-, tetra-, etc., to indicate the number of such substituents. Position numbers should be included for each substituent.

  1. Example 1-chloropropane

  2. Numbering starts from where the alkyl group gets less number as shown below the carbon to which halide group ( chloro) is added is on lower number on priority 1.

  4. Select longer chain as shown below. Give priority 1 to halide not methyl as shown below.
  6. first select longest chain, which is nonane in the given example below. In this example, both chloro and methyl is on number 3, but in correct side there is another substituent next to methyl group but there is no substituent next to halide ( chloro ) group. so, preferred numbering is 7- chloro-3,4-dimethylnonane. 3,4 beats 6,7. substituents getting lowest possible number.
  7. Place every substituent in alphabetical order.while placing in alphabetical order we dont consider di, tri, tetra, we only consider the main name.
  12. E is used for opposite
  13. Z is used for same side, for more details see stereochemistry.

  22. Practice problems


  25. Draw structures


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