Haloalkanes (Alkyl Halides)
(The classes of compounds, in which a carbon atom is connected to a halogen)
Structure & Types
Compounds, which contain a halogen (F, Cl, Br or I) covalently bonded to an sp3 hybridized carbon are called- haloalkanes and given a general formula of R-X. If the carbon is sp2 hydridized, then the compound is called a haloalkenes (vinyl halide); finally, if the carbon is part of an aromatic ring, then the compound is a haloarene (aryl halide).
(Chloroethylene or vinyl chloride)
Basic IUPAC nomenclature-Haloalkanes: (See the home page for parent root names, prefixes & suffixes.)
1. Number the parent chain to give the substituent encountered first the lowest number, whether it is halogen or an alkyl group.
2. Indicate halogen substituents by the prefixes fluoro-, chloro-, bromo-, and iodo- and list them in alphabetical order with other substituents.
3. Locate each halogen on the parent chain by giving it a number preceding the name of the halogen.
The parent chain in this example is butane; numbering the carbons, such that the chlorine will be on carbon #1 will result in the name: 1-Chlorobutane.
In this example, the parent chain is still butane; now, numbering the carbons, such that the chlorine atoms are on carbons #1 & #2. Since there are two chlorines, the term dichloro- is used. However, to specify the exact position of the two chlorine atoms, the numbers are used: 1,2-Dichloro- is combined with butane to become the full, IUPAC name: 1,2-Dichlorobutane.
When the chlorines are on the same carbon, they are still given the lowest number, and the number is used twice: 1,1-Dichloro. When added to the parent chain, butane, the name becomes: 1,1-Dichlorobutane.
4. In haloalkenes, number the parent chain to give carbon atoms of the double bond the lower set of numbers.
This parent compound is a butene- the double bond is given the preference (priority) in the numbering, so it is a 1-Butene. With the carbon framework in place & numbered, the chlorine is on the #4 position and the name becomes: 4-Chloro-1-butene. Note, that it is necessary to specify where the double bond is placed as well as the chlorine atom.
This variation has the 2-butene parent name. Although the butene can be numbered from the other direction (i.e. left to right), the numbering is arranged such that the chlorines are positions 1 & 3 (as opposed to 2 & 4). Thus, the IUPAC name becomes: 2,3-Dichloro-2-butene.
EXERCISE: Write the IUPAC name for each of the following structures.
END OF SECTION
email questions & comments to: Dr. JA Colapret