Nitration of Methyl Benzoate.

An Experimental and Theoretical Investigation.*

Vince Rotello


The rate-limiting step in the nitration of an aromatic species involves the addition of an electrophile to an aromatic ring:

For monosubstituted benzenes, three products are possible (ortho, meta, and para). Since the rate-limiting step involves nucleophilic addition of the aromatic species to the nitronium cation, if we can determine which position on the aromatic ring is most nucleophilic, we can predict the regiochemistry of the reaction. Since nucleophilicity is determined by the availability of electrons, a good predictor of this property is electron density, with addition predicted for the position that has the highest electron density.

In this experiment we will use the SPARTAN* computer program to carry out an AM1 semi-empirical molecular orbital (MO) calculation to predict electron density. We will determine electron density by calculating the electrostatic charges at ring carbons in methyl benzoate. Electrostatic charges are derived from the attraction (or repulsion) that a point charge would feel towards a nucleus.

* This experiment was carried out in the first part of the second semester of the Chemistry Majors Organic Lab Course. A handout is given. The experimental part was taken from Williamson, Macroscale and Microscale Organic Experiments, 2nd Ed.

** SPARTAN is a product of Wavefunction, Inc.