| Abstract
| - Formaldehyde oxime ⇌ nitrosomethane tautomerism, isomeric nitrone, and their common cationsand anions are studied with Gaussian-2 theory using MP2(full)/6-31G* geometries and with densityfunctional theory using B3LYP/6-311+G**. Geometrical parameters, harmonic vibrational frequencies, relative stabilities, conformational stabilities, and ionization energies are compared withexperimental gas-phase data when available. The formaldehyde oxime ⇌ nitrosomethane tautomerism is compared with the amide ⇌ imidol, imine ⇌ enamine, keto ⇌ enol, and nitro ⇌ aci-nitrotautomeric processes. Solvent effects are estimated by the self-consistent isodensity polarizablecontinuum model (SCIPCM). The influence of hydrogen bonding interactions with the solvent isaddressed by including two water molecules. In the final evaluation, formaldehyde oxime is 15.8kcal/mol more stable than nitrosomethane when the aqueous solvation correction of 3.8 kcal/mol isapplied to the G2 energies. Unsolvated formaldehyde oxime is estimated to be 11.1 kcal/mol morestable than nitrone. The estimated gas-phase ionization energies (G2) are 362.5 kcal/mol forformaldehyde oxime, 350.6 kcal/mol for nitrosomethane, and 351.4 kcal/mol for nitrone.
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