4- Oxopyridine tautomers

As far as we are aware, this type of calculation has been performed for lactim and lactam tautomers of both 2- and 4-oxopyridines [(2), (3)] and for formamide (6a) and formimidic acid (6b) only (Schlegel et al., 1982 Scanlan et al., 1983). Since the calculations mentioned are expensive, one estimates the S a b,> value by comparison of the electronic energies calculated in the HF approximation only [(HF)8EAliq)L and even this has often been done by means of semiempirical methods [(CNDO/2i8 A B,... 

A good illustration of this type of discrepancy is presented in Tables I and II. In the case of 2-oxopyridine, semiempirical CNDO/2 and MNDO methods and ab initio HF/STO-3G calculations predict the lactim tautomer of the molecule to be more stable than the lactam one, while the MINDO/3 and HF/3-21G calculations give a reverse result. In view of the large uncertainty in the experimental value -1.3 10.5 kJ mole-1 (probably overestimated), it is not possible to draw any other conclusion than that the experimental values and the theoretical values are spanning the... 

Thermodynamic Quantities and Relative Electronic Energies 8 jq) for the Lactim (A) and Lactam (B) Tautomers of 2-Oxopyridine in the Vapor Phase (the Lactam Tautomer Considered as the Reference System)0... 

In Table III lists the steps in the quantum-mechanical computation for 2-oxopyridine. The HF/STO-3G calculation with the full-geometry optimization gives an electronic energy for the lactim tautomer lower than that of the lactam by 64.4 kJ mole-1 (step 1°). Calculations carried out with a better basis set (3-21G) and with full-geometry optimization give the lower energy for the lactam by 7.1 kJ mole-1 (step 3°). This can be... 

Both models mentioned have been used to investigate the simultaneous influence of electronic excitation and solvation (hydration) on the tautomeric equilibrium in the first two excited states of 2- and 4-oxopyri-dine tautomers (2a), (2b) and (3a), (3b). The relative stabilization energies A a,b( ) in the first two excited electronic states of the tautomers in question are given with the available experimental data in Table VIII. Comparison with experimental data can only be done for the second excited state (the appropriate experimental data for the first n - 7r state are not available). In the case of 2-oxopyridine the value of Af2a,2b( ) is estimated to be equal to -(5.4-11.7) kJ mole-1 from shifts of the absorption bands of the lactim and lactam tautomers of 2-oxopyridine and the... 

Theoretical calculations and matrix-isolation FT-IR studies of hydrogen-bonded complexes of molecules modeling c qosine or isocytosine tautomers. 7. 2-hydroxypyridine/2-oxopyridine complexes with H20 ... 

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