Mesoionic compounds — structure and NMR parameters

A theoretical study using ab initio triple‐zeta basis sets of some mesoionic compounds

“…The calculated charges for the cis and trans isomers reveal that N-3 carries a positive charge and the exocyclic nitrogen, in the X group, a negative charge in all cases studied. This is in agreement with our previous 14 N NMR measurements [1,[3][4][5]10] where a charged nitrogen atom gives a sharper signal than that observed from an uncharged nitrogen. The distribution of electronic charge around the ring atoms in positions 1 and 2 depends upon the position of the atom in question, its nature (oxygen always has a minus charge, sulphur always has a plus charge, nitrogen may have a plus or minus charge) and the nature of the other atoms in the ring as well as their relative positions.…”

“…In particular 15 N NMR studies have been extremely useful in the identification of specific structural data [1]. We have presented preliminary Gauge Invariant Atomic Orbitals Coupled Hartree-Fock (GIAO-CHF) studies of the 13 C, 15 N, 17 O and 33 S chemical shifts of some prototypes of mesoionic compounds, which have shown a linear relationship between the calculated and observed 15 N chemical shifts [2][3][4][5].…”

Isoselenocyanates: A Powerful Tool for the Synthesis of Selenium-Containing Heterocycles

“…1,3,4-Triazolium-2-selenolates 32 were prepared by the reaction of isoselenocyanates and phenyl hydrazine and then treatment with an aroyl chloride (Scheme 21) [43]. The structures were interpreted according to the comparative method used by Stefaniak et al [44,45], Bartels-Keith et al [46] and by Miller and Montanari [47]. …”