Safety of 1H-Pyrazole-5-carbaldehyde. 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 Theoretical studies on proton transfer reaction of 3(5)-substituted pyrazoles. Author is Najafi Chermahini, Alireza; Teimouri, Abbas.
The inter and intra mol. proton transfer reactions of a series of pyrazole derivatives have been studied by using d. functional theory (DFT) and MP2 methods implementing 6-311++G(d,p) at. basis set. The substituents have been selected to cover a wide range of electronic effects. Proton transfer process was studied for mechanisms including single proton transfer, double proton transfer and proton transfer assisted by a water or ammonia mol. The results showed single proton transfer reactions for interconversion pyrazole derivatives need highest activation energies in the range of 45.7 – 51.59 and 49.4 – 53.96 kcal/mol at B3LYP and MP2 levels, resp. It was found that for the 3-substituted pyrazoles, electron withdrawing groups form stronger dimers but in the 5-substituted tautomers electron donating groups form stronger hydrogen bond. The double proton transfer reactions between dimers were studied and transition states calculated The ranges of activation energies were found to be 17.51 – 19.36 and 17.02 – 17.80 kcal/mol for the C→E and D→D reactions resp. In addition, the activation energies for the proton transfer reaction assisted by water or ammonia mols. were found to be in the range of 26.62-31.78 and 17.25 – 22.46 kcal/mol, resp., calculated at MP2/6-311++G(d,p) level of theory.
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