Why is the hydrogenation of benzene possible, but the addition of bromine to benzene is not?

1. Why is the hydrogenation of benzene possible, but not an addition of bromine to benzene?

• Hydrogenation of benzene:benzene can actually be hydrogenated, but it requires high pressure and a catalyst. In this reaction, benzene is hydrogenated to cyclohexane. However, it is important to note that benzene has a high aromatic stability due to its delocalized π electron system. Therefore, direct hydrogenation under normal conditions is not easily possible.
• Addition of bromine to benzene: benzene does not react in a typical electrophilic addition with bromine, as other alkenes would do. This in turn is due to the special aromatic stability of benzene. However, if benzene is treated with bromine in the presence of a catalyst such as iron bromide (FeBr3), an electrophilic aromatic substitution takes place in which a hydrogen atom of benzene is replaced by a bromine atom, and not a direct addition. This leads to the formation of bromobenzene.

2.Why is a poorer energy state more stable?

The basic principle here is the tendency of systems to minimize their overall energy condition. A lower energy system is more stable because it has less potential energy that can be converted into kinetic energy. It is comparable to a ball lying on a hill: a ball lying down the hill (which corresponds to a lower energetic condition), has a lower potential to roll down and is therefore in a more stable position than a ball on top of the hill.

A simple example of chemistry is the formation of molecules from atoms. Atoms connect to molecules because they can thereby enter an energetically more favorable (and thus more stable) state by sharing or transmitting their electrons.