If two different alkyl halides are used in Wurtz reaction to prepare an alkane with odd number of carbon atoms, a mixture of three alkanes is actually 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. The boiling point of these alkanes are very close as molecular mass is almost same and hence they cannot be separated by fractional distillation. It is because of this drawback that Wurtz reaction is used for synthesis of symmetrical alkanes and not for the preparation of unsymmetrical alkanes.