Electronic structure is shown for the oxygen, sulfur, and nitrogen atoms in the five-membered aromatic heterocycles furan, thiophene, and pyrrole. In these
ring systems the heteroatom contributes a pair of electrons to the π system, which together with four electrons contributed by the four carbon atoms
(carbon p orbitals not shown) complete a sextet of π electrons and make the ring systems aromatic.
Source: The Nature of Bonding in Organic Molecules, The Organic Chemistry of Medicinal Agents
Citation: Renslo A. The Organic Chemistry of Medicinal Agents; 2016 Available at: http://mhmedical.com/ Accessed: July 31, 2017
Copyright © 2017 McGraw-Hill Education. All rights reserved