2-Pyridone-2-hydroxypyridine

Scheme 2.5 Self-assembly through hydrogen bonding of the 2-pyridone/2-hydroxypyridine system 1 (6-DPPon) to generate bidentate ligand metal complexes 3 for homogeneous catalysis.

Chou. P.-T, Wie, C.-Y. and Hung, F.-T. (1997) Conjugated dual hydrogen bonds mediating 2-pyridone/2-hydroxypyridine tautomerism. J. Phys. Chem. B, 101, 9119-9126. 

Meuwly, M., Muller, A. and Leutwyler. S. (2003) Energetics, dynamics and infrared spectra of the DNA base-pair analogue 2-pyridone 2-hydroxypyridine. Phys. Chem. Chem. Phys., 5, 2663-2672. 

Observations analogous to those for carboxylic acid dimers have been reported for 2-pyridone-2-hydroxypyridine (2PY-2HP) [52, 53], illustrated in Fig. 29.9. This dimer, formed from two isomers, is asymmetric, but it has a symmetric double proton transfer potential since the transfer interchanges the isomers. In a collaborative effort, Pratt, Zwier, Leutwyler and their coworkers [52] measured and analyzed the high-resolution fluorescence-excitation spectrum of the origin... 

Figure 29.9 Calculated structures of the equilibrium configuration and the transition state of the 2-pyridone 2-hydroxypyridine dimer in the ground state and the excited state [29], Pertinent bond lengths are given in A the numbers in parentheses refer to the equilibrium configuration of the excited state.

In an ab initio study of the tautomerism of 2- and 4-hydroxy-pyridines, 4,-hydroxypyridine was calculated to be 2.4 kcal/mol more stable than 4-pyridone. 2-Pyridone was calculated to be 0.3 kcal /mol more stable than 2-hydroxypyridine and this is in good agreement with experimental values obtained from tautomeric studies in the gas phase.61 A study of the bromination of the 2-pyridone/2-hydroxypyridine system has revealed that reaction occurs via the principal "one" tautomer at pH<6 and via the conjugate anion at pH>6. Attack on the "one occurs preferentially at the 3-position, whereas on the anion it probably occurs mainly at the 5-position. The facile formation of 3i5-dibromo-2-pyridone results from the comparable reactivity of the monobromopyridones at pH<1 and pH>4- Practical procedures have been reported for the preparation of 3-bromo-2-pyridone and... 

For example, for the keto-enol equilibrium 2-pyridone = 2-hydroxypyridine, dipole-in-a-sphere QCISD/6-31+G energy calculations at HF/6-31G geometries optimized both in the gas phase and in solution with cavitation and dispersion contributions omitted give the following values at 298 K in the gas phase and in the solvents cyclohexane (s = 2.0) and acetonitrile (e = 36) AG° = -0.6,0.4, and 2.3 kcal/mol, respectively, compared with the estimated experimental values -0.8, 0.3, and 3.0 kcal/mol [M. W. Wong, K. B. Wiberg, and M. J. Frisch, /. Am. Chem. Soc., 114, 1645 (1992)]. TTie more-polar keto form 2-pyridone (calculated gas-phase fi = 4.2 D) was stabilized more than the enol form (calculated gas-phase fi = 1.5 D) in solution. 

The compound 2-hydroxypyridine, a derivative of pyridine, is in equilibrium with 2-pyridone. 2-Hydroxypyridine is aromatic. Does 2-pyridone have comparable aromatic character Explain. 

A., and Leutwyler, S. (2002) Hydrogen bonding and tunneling in the 2-pyridone- 2-hydroxypyridine dimer, effect of electronic excitation. Chem. Phys., 112, 3717-3726. 

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