Of 2-bromo-3-methylbutane , 2-chlorobutane , 2-chloro-2-methylpropane, which haloalkanes will give 3,4-dimethylhexane when treated with sodium metal (Wurtz reaction)? Write the reaction equation?

Start with 2-chlorobutane.

You could solve this problem by writing the equation for each reactant, and seeing which one gives the desired product.

It is often easier to do a retrosynthesis.

That is, we work backwards from the products to figure out what the starting materials must be.

The Wurtz synthesis is

##"R-X + 2Na" → "R-R + 2NaX"##

So, we could write

##"R-R" ⇒ "R-X + X-R"## (⇒ means "implies" or "can be made from").

For your problem, we could write

##"CH"_3"CH"_2"CH(CH"_3")-CH(CH"_3")CH"_2"CH"_3 ⇒ "CH"_3"CH"_2"CH(CH"_3")-X" + "X-CH(CH"_3")CH"_2"CH"_3##

If you look at the list of starting materials, yours must be ##"CH"_3"CH"_2"CH(CH"_3")-Cl"##, 2-chlorobutane.

The equation for the reaction is then

##"CH"_3"CH"_2"CH(CH"_3")-Br" + "2Na" + "Br-CH(CH"_3")CH"_2"CH"_3 → "CH"_3"CH"_2"CH(CH"_3)"-CH(CH"_3")CH"_2"CH"_3##