Note on Nomenclature and isomerism of haloalkane

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Nomenclature.

In the commons system , the mono halogen derivatives of alkanes are called alkyl halides. The common names of the mono halogen derivatives of alkanes are two-word names: the name of the alkyl group is followed by the word fluoride, chloride, bromide, or iodide depending upon the nature of the halogen.

In the IUPIC system, the mono halogen derivatives of alkanes are named as haloalkanes, I,e the name can be obtained by prefixing the word halo to the name of the alkane corresponding to longest continuous carbon chain holding the halogen atom. In a case of branched chain alkanes, the following rules are followed.

  1. The longest continuous carbon-containing the carbon attached to halogen is selected as the parent chain.
  2. The carbon atoms of the parent chain are numbered in such a way that the carbon atom carrying the halogen atom gets the lowest number.
  3. The position of the halogen atom and other substituents (alkyl groups) are indicated by the number of the carbon atom to which they are attached.

The two system of nomenclature is illustrated below by the names of some mono halogen derivatives of alkanes.

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Isomerism in haloalkane.

Following two types of isomerism is possible in haloalkane.

  1. Chain isomerism.
  2. Position isomerism.

Chain isomerism.

Chain isomerism arises due to the different structure of carbon skeleton in the largest chain . Haloalkane containing at least four C-atoms gives chain isomers.

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Positional isomerism.

Position isomers are formed due to different positions of functional groups or substation. Haloalkane containing at least 3 carbon atoms can form position isomers.

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A haloalkane M reacts with aq NaOH to give isopropyl alcohol. What major product would you get when M is heated with Na in presence of dry ether.

Answer.

Since the haloalkane M reacts with aq NaOH to give isopropyl alcohol, the haloalkane should be 2-halopropane.

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Reference.

Bahl, B S, Bahl, and Arun. Advanced Organic chemistry. S. Chand and company Ltd., n.d.

Sthapit, M K, R R Pradhananga, and K B Bajracharya. Foundations of chemistry. Taleju Prakashan, n.d.

Tewari, K S, S N Mehrotra, and N K Vishnoi. A textbook of organic chemistry. Vikash publishing House Pvt. ltd., n.d.

Verma, N K and S K Khanna. Compressive chemistry. 8th edition. Laxmi publications P. Ltd., 1999.

  1. In the commons system , the mono halogen derivatives of alkanes are called alkyl halides.
  2. In the IUPIC system, the mono halogen derivatives of alkanes are named as haloalkanes,
  3. The longest continuous carbon-containing the carbon attached to halogen is selected as the parent chain.
  4. Haloalkane containing at least four C-atoms gives chain isomers.
  5. Haloalkane containing at least 3 carbon atoms can form position isomers.

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