An ab initio study of the H₂O-mediated 1,3-hydrogen rearrangement in the isoelectric series: X, Y = CH₂, NH, or O

Abstract

. Can. J. Chem. 69, 1589 (1991). Ab initio calculations are performed to investigate the effect of water on the 1,3-intramolecular hydrogen rearrangement in the H X X H = Y + X=CH-YH isoelectronic series, for X, Y = CH2, NH or 0 , by modeling with a single H 2 0 molecule. The geometries for the complexes are optimized at both the 3-21G and 6-31G** basis set levels. MP2 and some MP4 calculations are performed to take into account the correlation effects, and ZPV corrections are calculated at the MNDO level. The results show that the water molecule has a significant effect on the molecules in which hydrogen bonds can be formed or partially formed. The "solvent effects" are also examined using the self-consistent reaction-field (SCRF) approach. A combination of supermolecule and SCRF approach appears to work well at predicting the effect of solvent on relative stabilities and baniers.

Ab initio study of the electronic properties of potential antagonists of the glycine receptor: 1. Transition state of the 2‐pyridone · H2O/2‐hydroxypyridine · H2O tautomeric equilibrium

“…Table I indicates that our value of -2.91 kcal mol-' favors the hydroxyl form and predicts a reversal of stability for the hydrated system. This is in accordance with the result of Poirier et al [7] who also favors the hydroxyl form for the formamidic acid HzO. The tautomeric energy of -0.54 kcal mol-' for the gas-phase system is consistent with the wrong predictions made at this level of theory [8].…”

“…The structures for the supermolecules were optimized at the 3-216 split valence-shell basis-set level [15]. The starting geometries were built from the supermolecules computed by Poirier et al [7] for the formamide/formamidic acid system and by adding the missing aromatic ring to build the pyridone/hydroxypyridine system. Single-point calculations at the 6-31~* polarized basis set level [16] were subsequently performed on the optimized structures.…”

“…Interestingly, pyridones (111) and pyrimidones (IV) can be related to the tautomerism of nucleic acid bases, and recent theoretical investigations have constituted solid references for our studies. An ab initio study of the water-mediated 1,3-hydrogen rearrangements [7] demonstrated the effect of water on molecules where hydrogen bonds can be formed and interestingly applied the do a: T "XI T self-consistent reaction field (SCRF) approximation to estimate the effect of solvation on transition-state calculations. Tautomeric equilibria of formamide and 2-pyridone in the gas-phase and solution were also investigated recently using high-level ab initio molecular orbital studies, taking into account the solvent effects by the SCRF method [8].…”

Hartree−Fock and Density Functional Methods and IR and NMR Spectroscopies in the Examination of Tautomerism and Features of Neutral 9-Acridinamine in Gaseous and Condensed Media

“…The occurrence of these processes could cause the tautomeric equilibrium between 9-AA and 9-AI to be achieved in the CD 3 CN liquid phase (as the theoretical predictions on the HF level indicate). In such a case signals in the experimental NMR spectra could arise from a metastable transition state formed upon rapid exchange of two H atoms between two 9-AA or 9-AI molecules, or one H atom through a bridge of water (solvent) molecules spread between the N atoms of one 9-acridinamine molecule . In such a state the signals could be the resultant of those originating from both 9-AA and 9-AI.…”

High-Level ab Initio Molecular Orbital Calculations of Imine Formation

“…The water molecules are involved directly, facilitating the proton-transfer process through six- and eight-membered ring transition states with one and two waters, respectively. Similarly, water molecules have been shown to dramatically reduce the barriers in the ketonization of vinyl alcohol , and several other 1,3-hydrogen rearrangement reactions. , …”