Electric Literature of C4H4N2O. The protonation of heteroatoms in aromatic heterocycles can be divided into two categories: lone pairs of electrons are in the aromatic ring conjugated system; and lone pairs of electrons do not participate. Compound: 1H-Pyrazole-5-carbaldehyde, is researched, Molecular C4H4N2O, CAS is 948552-36-1, about The theoretical determination of heats of formation, proton affinities and gas basicities of N and C-substituted pyrazoles: analysis of the substituent effects on the gas-phase basicity. Author is El Hammadi, A.; El Mouhtadi, M..
The MP2(FC)/6-31G* energies calculation, with complete optimization geometries at RHF/6-31G* level, was carried out on the neutral and protonated forms of C and N-mono-substituted pyrazoles (28 R-C(n)Pz and 12 R’-NPz with n = 3, 4 and 5; R = R’=H, Me, CHO, CN, NH2, NO, NO2, OH, F and Cl, and R’=Et, Pr and Ph) and some related compounds (Pyridine, 2-methylpyridine, 3-methylpyridine, Pyrrole and N-methylpyrrole). The heats of formation (using isodesmic reaction), the proton affinities (PA) and the gas basicities (GB) were determined for pyrazole derivatives The results are consistent with the exptl. evidence and provide a better understanding of the structures and energies for mono-substituted pyrazoles. Also, the RHF/6-31G* geometrical parameters are compared with those obtained by AM1 method, the agreement is satisfying. Linear relations are found between AM1 and MP2(FC)/6-31G*//6-31G* for heats of formation and for PAs of R-C(n)Pz and R’-NPz. Many pyrazole derivatives fit correlation well. Also, the structures and heats of formation for sizeable N-mono-substituted pyrazoles (17 compounds), which are interesting in chem. area, was also optimized by AM1, their PAs are scaled with a reasonable precision. Substituent electronic effects (SE) was analyzed in terms of polarizability, field, and resonance contributions using the Taft-Topsom model. The SE on N atom N(1) differs notably from those on C atoms C(3), C(4) and C(5). The origin of this difference was discussed yet.
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