Pi-Deficient Aromatic Heterocycles

Some Physical Properties of Pyridine. Pyridine is a liquid with a rather low boiling point of 115°C. It is infinitely miscible with water, attesting to its polar character from inductive and resonance effects (section 6.3.1.2). Pyridine has a strong odor, which most find to be obnoxious. [Pg.138]

Electronic Structure of Pyridine. The presence of the electron-withdrawing nitrogen atom in pyridine has a profound effect on its properties. The resonance picture of benzene can be applied to pyridine as in hybrid 6,2. [Pg.138]

However, the electronegative nitrogen atom causes significant polarization of the molecule, as depicted in stmcture 6.3. [Pg.138]

The combined action of electron induction and resonance delocalization makes pyridine a molecule of considerable polarity. It has a dipole moment of 2.20 Debye (D) units. This value might be compared with that of piperidine (1.57 D), whose polarity is controlled only by induction. Pyridine finds many uses as a nonprotonic polar solvent. [Pg.140]

The carbon-13 NMR spectrum of pyridine of course also has three signals for the different carbons, but these show no coupling to each [Pg.141]

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