Aromatic Heterocycles---Pyridine Heterocyclic aromatic compound. Nonbonding pair of electrons in sp2 orbital,so weak base,p=8.8. Lone pair in Pyridine (Six electrons) sp2 orbital (sp2) Lone pair +H2O *_H +OH +H20 +-OH pyridine,pp=8.8 pyridinium ion.pK=5.2 Copyright2005 Pearson Prentice Hall.Inc. Aromatic Heterocycles ---Pyridine ❖Heterocyclic aromatic compound. ❖Nonbonding pair of electrons in sp2 orbital, so weak base, pKb = 8.8