Question

In alkyl halide X reacts with sodium to form 3,8-dimethyl decane. What is X?
(A)

(B)

(C)

(D)

Answer 1

Hint: Alkyl halides on treatment with sodium metal in dry ethereal (free from moisture) solution give higher alkane. This reaction is known as the Wurtz reaction and is used for the preparation of higher alkanes containing an even number of carbon atoms.

Complete answer:
According to Wurtz reaction, two metal halides react in the presence of sodium metal and dry ether solution will form higher alkanes.
Applying this statement to all compounds given and let us see with alkyl halide will give the product 3,8-dimethyl decane.
(A) the IUPAC name of this compound is chloro-3-methyl pentane.
If this compound obeys the Wurtz reaction rule, reacts with sodium metal in the presence of dry ether solution, the reaction follows,

 (B) The IUPAC name of this compound is chlorobutane. If this compound obeys the Wurtz reaction rule, the product is n-octane.
(C) the IUPAC name of the given compound is chloro-2,3-dimethyl heptane.
If this compound obeys the Wurtz reaction rule, while react with Na metal the product is 2,3,8,9-tetramethyl tetradecane.
(D) The IUPAC name of this compound is chloro-2,2-dimethylbutane.
If this compound obeys the Wurtz reaction rule, while reacting with Na metal the product is 2, 2,5,5- tetramethyl octane.
From all four compounds, option A is (the correct answer) the alkyl halide X.

Note:
If two different alkyl halides are used in Wurtz reaction to prepare an alkane with an odd number of carbon atoms, a mixture of three alkanes is produced. The reason is that the two alkyl halides, in addition to reacting with each other also react among themselves giving a mixture of three alkanes.