Why is Wurtz reaction not suitable for the preparation of odd number alkanes ?

Explanation

Wurtz reaction is generally used for making symmetrical alkanes containing even number of carbon atoms. For example,

If we try to make as alkane with odd number of carbon atoms by this method, the yield of desired alkane is very poor as two more alkanes are also obtained as by products. Further separation of desired alkane from byproducts is also difficult. For example if we try to make propare by Wurtz reaction, ethane and butane are formed as by products.