The Concept of Resonance
There are many compounds for which the classical formula (Lewis structure) is apparently not consistent with the observed chemical behaviour. For example, an aminoaldehyde such as 3-aminopropanal has properties of both an amine and a carbonyl compound, and is well represented by the formula Open image in new window . But propanamide, which also has an amino group and a carbonyl group in its structure, Open image in new window , is appreciably less basic than an aliphatic amine, and does not react at all with many of the reagents (weak nucleophiles) which attack the carbonyl group in aldehydes and ketones. It would appear that when these two functional groups are adjacent to one another, they are each able to modify the properties of the other in a way which would not be predicted from the Lewis formula*.
Unable to display preview. Download preview PDF.