Seite - (000032) - in Biomedical Chemistry: Current Trends and Developments

Figure 1.1.4: Clarification of the aromatic stabilization of benzene. Hypothetically, cyclohexatriene would have two different types of bonds: simple and double bonds, but spectroscopic data show that all bonds are equivalent. The bonds in benzene have an intermediate character between a simple and a double bond with the electrons delocalized (density evenly distributed). Figure 1.1.5: Cytosine is an example of a biomolecule exhibiting aromaticity in its imidic acid form. Furan is an example of a heteroaromatic compound where a lone pair of electrons of the heteroatom is delocalized into the ring to allow aromaticity. The Fig. explicitly shows all the resonance forms in the rings of the compounds. 1.1.4.3.1 Electrophilic Aromatic Substitution A strong electrophile may capture electrons from the ring, forming a very unstable intermediate. Since the loss of aromaticity is energetically unfavourable, a nucleophile does not add to the cation. Instead, the ring eliminates a proton (Scheme 1.1.12).