Tetrahedron p. 4663 - 4668 (1987)
Update date:2022-08-16
Topics:
Bruix, Marta
Mendoza, Javier de
Elguero, Jose
The H-5 signal of N-substituted pyrazoles is not shifted to low field values on increasing solvent polarity when a nitrogen lone pair lies very close to the measured proton (H-bond).Typical examples of this "abnormal" behaviour are provided by C,N'-linked, pyrazole-containing heterocyclic dimers.On the contrary, models selected in the 1,1'-bipyrazole and 2,2'-biindazole series (N,N'-linkage) showed normal shifts, due to their non-coplanar conformation around the N-N bond.For the assignment of disubstituted pyrazoles, a proton-coupled (13)C n.m.r. spectrum is recommended as an alternative method.
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Doi:10.1002/etc.5620130401
(1994)Doi:10.1002/aoc.4831
(2019)Doi:10.1007/s10562-013-1184-2
(2014)Doi:10.1007/BF00900446
(1954)Doi:10.1016/S0960-894X(99)00636-8
(2000)Doi:10.1246/bcsj.60.2271
(1987)
