7 research outputs found
Energetic Study of 4(3<i>H</i>)‑Pyrimidinone: Aromaticity of Reactions, Hydrogen Bond Rules, and Support for an Anomeric Effect
4(3<i>H</i>)-Pyrimidinone
is observed in nature in equilibrium
with other tautomeric forms, mimicking the tautomeric equilibrium
in pyrimidine nucleobases. In this work, the enthalpy of formation
in the gaseous phase of 4(3<i>H</i>)-pyrimidinone was derived
from the combination of the enthalpy of formation in the crystalline
phase, obtained by static bomb combustion calorimetry, and the enthalpy
of sublimation, obtained by Knudsen effusion. The gaseous phase enthalpy
of formation of 4(3<i>H</i>)-pyrimidinone was interpreted
in terms of isodesmic reactions that consider the enthalpic effects
of hydroxypyridines and pyrimidine. After comparison of the experimental
and computational results, the same type of isodesmic reactions was
used to study the substituent effects of the hydroxyl functional group
of 2-, 4-, and 5-hydroxypyrimidines. The influence of aromaticity
on the energetics of hydroxypyrimidines was evaluated using the variation
of nucleus-independent chemical shifts for several reactions. The
influence of intramolecular hydrogen bonds was investigated using
the quantum theory of atoms in molecules and the geometric rule of
Baker and Hubbard to identify hydrogen bonds. The energetic results
obtained were also interpreted in terms of an <i>in plane</i> anomeric effect in the pyrimidine ring