For this assignment, the target compound that you should synthesize is 1-methyl-4-nitro-benzene. This is an electrophilic aromatic substitution reaction. Examine the product carefully and determine the substitution pattern. Which group will already be present in the substrate? Keep in mind the mechanism and how that will control the selectivity of the process. Remember, you can easily separate ortho and para isomers.

The methyl group will already be present  

Explanation:

You want to make 1-methyl-4-nitrobenzene.

The question is, "Do I start with the methyl group on the ring and then nitrate, or do I start with the nitro group on the ring and then add the methyl group?"

The methyl group is activating and ortho, para directing.

The nitro group is deactivating and meta directing.

You want a para-substituted product, so you choose to nitrate toluene, as in the reaction scheme below.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.