I've already subtracted the weight of the vials so that only the weight of the compounds are shown
15 EXPERIMENT STUDYING THE EFFECTS OF SUBSTITUENTS ON ELECTROPHILIC AROMATIC SUBSTITUTION REACTIONS: COMPETITIVE NITRATION 0 In this experiment the effect of two different substituents will be examined by studying the outcome of nitra- tion on substituted benzene rings. You need to review the sections of your lecture text dealing with aromatic substitution reactions before coming to lab. The general mechanism for electrophilic aromatic substitution (EAS) reactions is shown in Scheme 15.1. It should be noted that this mechanism is the same regardless of the identity of the electrophile (E). In the EASs reaction, the E+ functions as a Lewis acid, and the Ï electrons of the benzene ring serve as the Lewis base. This reaction is nothing more than a series of Lewis acid/Lewis base reactions. Recall that aromatic systems such as benzene do not readily undergo addition reactions because the resulting products would lose their aromatic stability. However, the EAS reaction allows the resulting product to maintain aromaticity The gen- eration of the nitronium ion (NO2") is also depicted in Scheme 15.1. It is a bit counterintuitive to beginning chemists to think of the strong acid, nitric acid, as a Lewis base. However, one must recall that a Lewis base is merely an electron pair donor and that a Lewis acid is an electron pair acceptor. You should note in Scheme 15.1 that a lone pair of electrons from nitric acid are being donated to a proton from sulfuric acid, hence this makes nitric acid a Lewis base in this vital reaction. 83
