4-1-Bromobenzene Lab Report

For this experiment, a nitro arene was prepared and then the relative rates of bromination for a set of arenes was observed. Electrophilic aromatic substitution is the reaction of an electrophile with an aromatic ring to form a new bond between the aromatic ring and the electrophile. Two experiments were performed.
First, the preparation of 4-nitro-1-bromobenzene takes place through a nitration of bromobenzene. The bromobenzene in this reaction will be treated with both sulfuric and nitric acid. These two strong acids mix together to form a nitronium ion intermediate which is extremely electrophilic. The strong electrophile is needed since the first mechanistic step of the electrophilic aromatic substitution reaction results in a loss or aromaticity

The carbon containing the positive charge attaches to the functional group. The functional group is bonded to an oxygen with lone pairs that can be donated instead of to a carbonyl carbon with a partial positive charge. Therefore, four possible resonance structures can be formed. With ortho, there are four resonance structures created. In meta, there are three resonance structures because the positive charge is on the alcohol group for this example and never lies on the carbon attached to the functional group. In para, the positive charge can be on the carbon connected to the functional group, so four resonance structures can form. The dominant products of the electron releasing groups are ortho and para substitution because four resonance structures are produced. Therefore, electron releasing groups activate both ortho and para

The rate at which they reacted was predicted based on an order of 1-5 prior to the experiment. The rates were determined by the rate at which the solutions changed from orange to colorless. In this experiment, 15 M of acetic acid was used as the solvent. This is an unusual solvent, but it was used since everything can be soluble in it allowing for a reaction to take place. DCM could have been used because all of the reactants are soluble in it including bromine, but it was not used since the aromatic ring attacks the electrophile resulting in a loss of aromaticity temporarily. The electrophile needed to be strong in order to cause there to be a temporary loss of aromaticity, so it could become energetically favorable. The reaction was increased and sped up. When adding heat to the system, it adds energy which can be problematic. In the Fischer esterification experiment, stronger reactants were used. If using DCM, the lab would take a longer amount of time for the reaction to be completed. Bromine is a very good electrophile so upon adding the protons to the solution, the lone pairs of electrons make a partial bond which causes there to be a shift in the direction of the electron density. Therefore, this creates a partially positive bromine atom that increases its