||Chapter 11 : Arenes and Aromaticity
- Aromaticity is the property
associated with the extra stability of certain types of π systems. Such systems are said to be "aromatic".
- Fundamentally it arises
from having the maximum number of electrons in the pi bonding molecular orbitals.
As we will see, it is not restricted to benzene, substituted benzenes, 6-membered
rings or just even hydrocarbons.
- The property of aromaticity is
generally due to the significant extra stability
associated with a resonance delocalised structure.
- This extra stability moderates
the reactivity of these systems compared to alkenes and means aromatics can
and should be considered to be their own functional group.
- The presence of aromatic systems
can also influence the reactivity of functional groups directly attached to
the aromatic system particularly in the benzylic position. Therefore it is
important that you are able to recognise the aromatic systems.
We will review how to identify which classification applies later in this chapter. We are just defining the terms here:
- Compounds that have this extra stability as said to be "aromatic" e.g. benzene.
- Compounds that don't have extra stability and just have normal stability are "non-aromatic" e.g. cyclohexene.
- Compounds that are unusually unstable are said to be "anti-aromatic" e.g. 1,3-cyclobutadiene