Question

In alkyl halides, the homologous series of alkyl halide is represented as:
  (A) ${{C}_{n}}{{H}_{2n+1}}X$
  (B) ${{C}_{n}}{{H}_{2n+4}}X$
  (C) ${{C}_{n}}{{H}_{2n+3}}X$
  (D) ${{C}_{n}}{{H}_{2n+2}}X$

Answer 1

Hint: In alkyl halides or haloalkanes the halogen atom is bonded to the alkyl group(R-X).They can be formed by removing a hydrogen atom from the homologous alkanes. Thus by knowing the representation of homologous alkanes, we would be able to find the representation of homologous series for alkyl halides.

Complete step by step answer:
- Let us in detail try and understand about alkyl halides. They are also known as haloalkanes. They are the compounds in which one or more hydrogen atoms in alkanes is replaced by halogen atoms such as chlorine, bromine, iodine etc.
- For naming the alkyl halides the IUPAC system is used in which the name of parent alkane with a prefix indicating the halogen substituents, preceded by the number which indicates the location of substituent.
 - In organic chemistry, a homologous series can be defined as the sequence of compounds with the same functional groups which gives them similar physical and chemical properties.
 -In straight chained alkanes, the homologous series will begin with methane and as the series goes on the excessive member will differ by an extra methylene group ($-C{{H}_{2}}$) inserted in the chain. Hence alkanes can be represented by the general formula ${{C}_{n}}{{H}_{2n+2}}$ .
 - As we mentioned, the replacement of only one hydrogen atom will give us alkyl halides. When one hydrogen atom is replaced by a halogen atom(X), we can modify the above representation as${{C}_{n}}{{H}_{2n+1}}X$ and this represents the homologous series of alkyl halides.
So, the correct answer is “Option A”.

Note: It should be noted that the alkyl halides can be further classified as primary, secondary and tertiary according to the nature of the carbon atom to which the halogen atom is attached. The most common examples of haloalkanes or alkyl halides are 2-chlorobutane, 1-fluoropropane, and tribromomethane etc.