Electron excess heteroaromatic
An electron excess heteroaromatic is a heterocyclic aromatic compound with a π excess heterocycle. Pyrrole is a typical representative of the π-excess heteroaromatic compounds. The free electron pair on the nitrogen atom of the pyrrole forms with the four p electrons of the carbon atoms an electron sextet of cyclically delocalized electrons, i.e. an aromatic . In the dipolar boundary structures involved in mesomerism , the N atom has a positive charge and every C atom in the ring has a negative charge:
The π electron density at the carbon atoms of pyrrole is greater than 1 (that of benzene). The dipolar resonance structures of the pyrrole molecule are also consistent with the observation that pyrrole - unlike amines , such as. B. Pyrrolidine - is not a base, but a weak acid; p K s = 17.5).
Individual evidence
- ^ A b Albert Gossauer: Structure and Reactivity of Biomolecules , Verlag Helvetica Chimica Acta, Zurich, 2006, pp. 468–469, ISBN 978-3-906390-29-1 .