Barriers to the intramolecular N‐ to N‐transfer of different groups in pyrazoles: Prototropy vs. Elementotropy

Abstract

Barriers to the N-to N-transfer of different groups in pyrazole have

Substitution effects on neutral and protonated pyridine derivatives along the periodic table

“…1b). Similar results were obtained previously for the pyrazole analogues [5]. In the present study, the planar structure is more stable for the boron derivative, while the perpendicular structure is preferred for aluminum.…”

“…In two recent articles, we have studied the influence of all elements of the second and third rows of the periodic table as substituents of benzene, N-pyrrole, N-pyrazole and N-imidazole [1,2]. Further theoretical studies were devoted to the properties of a selection of pyrazole derivatives; in particular to geometries and methyl stabilization energies [3], GIAO calculations [4] and metallotropic rearrangements [5]. All heterocycles studied thus far belong to the family of p-excessive systems according to Albert's classification [6,7].…”

Substitution effects in N-pyrazole and N-imidazole derivatives along the periodic table

“…In a recent article, we have studied the influence of all the elements of the first, second, and third row of the periodic table as substituents of benzene and N-pyrrole [1]. Other theoretical studies were devoted, in particular, to the properties of a selection of derivatives of pyrazoles, particularly geometries and methyl stabilization energies [2], GIAO calculations [3], and metallotropic transpositions [4].…”

Five‐Membered Heterocycles: 1,2‐Azoles. Part 1. Pyrazoles

“…For instance, substituents like NO 2 and CO 2 Me at position 3 favor the 2H-tautomer, the replacement of a CH by an N atom at position 7 favors the 1H-tautomer (by lone-pair/lone-pair repulsion in 7b), and a fused benzo group at positions [ f ] and [g] favors, respectively, the 1H-(8a) and 2H-tautomers (9b). [41]. Other groups on the nitrogen migrate either intermolecularly (COR, CH 3 , etc.)…”

“…Other groups on the nitrogen migrate either intermolecularly (COR, CH 3 , etc.) or intramolecularly (SiR 3 , GaR 2 , GeR 3 , SnR 3 , HgR) with barriers that can be very low in some cases [34,41]. 4) The tautomerism of functional derivatives, such as pyrazolones, is well understood and is no longer a research subject [32,34].…”