From 2-Hydroxypyridine to 4(3H)-Pyrimidinone: Computational Study on the Control of the Tautomeric Equilibrium

Abstract

In this work is investigated why the entrance of a nitrogen atom in the ring of cis-2-hydroxypyridine and 2-pyridinone, resulting in cis-4-hydroxypyrimidine and 4(3H)-pyrimidinone, respectively, shifts the tautomeric equilibrium from the hydroxyl form, in the pyridine derivative, to the ketonic form, in the pyrimidine derivative. The conclusions obtained for these model systems allow us to understand how to control the gaseous-phase keto-enol tautomeric equilibrium in nitrogen heterocyclic rings and justify the tautomeric preference in pyrimidine nucleobases. The experimental and computational energetics of tautomeric equilibrium were interpreted in terms of the aromaticity, intramolecular hydrogen bonds, and electronic delocalization, evaluated using nucleus independent chemical shifts, quantum theory of atoms in molecules, natural bond orbital analysis, and the thermodynamic changes of appropriate reactions.

When does a hydrogen bond become avan der Waalsinteraction? a topological answer

“…Having studied the NCI boarder between H‐bond and vdW upon elongation of R A ⋯ D , it was worth considering the second geometric parameter typically used to define H‐bonds: angle θ ( D − H ⋯ A ), see Supporting Information Figure S3. As already showed by Galvão et al, closing θ ( D − H ⋯ A ) to a certain degree, A ⋯ H BCP shifts from the straight line between A and H going close to the straight line between A and D . This is due to the strongest interaction between the electronic clouds of more electronegative A and D with respect to direct interaction between A and H when A and D are at sufficient distance.…”

“…This is due to the strongest interaction between the electronic clouds of more electronegative A and D with respect to direct interaction between A and H when A and D are at sufficient distance. Galvão et al seen this shifting angle degree θ ( D − H ⋯ A ) of 120.00 and associated it to the end of H‐bond interaction calling it: “critical angle.”…”

Thermochemical study of dichloromethylpyrimidine isomers

“…Recently, we have been involved in an extensive research project on the thermodynamic properties of pyrimidines [16][17][18][19][20], cytosine [21], uracil [22][23][24][25][26][27][28] thiouracil [29,30] and barbituric acid derivatives [31]. In this context, the present work complements the previous ones and reports the standard (p o = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, of four dichloromethyl substituted pyrimidines: 2,4-dichloro-5-methylpyrimidine, 2,4-dichloro-6-methylpyrimidine, 4,6-dichloro-2-methylpyrimidine and 4,6-dichloro-5-methylpyrimidine.…”

Decarbonylation of the 2-Hydroxypyridine Radical Cation: A Computational Study

“…[1][2][3][4][5] In the gas phase, 2-HP is slightly more stable than 2-PY, while the 2-HP radical cation (2-HP…”