MNDO molecular orbital study of nitrenium ions derived from carcinogenic aromatic amines and amides

Syn andanti aryl nitrenium ions

“…A similar conclusion was reached on the basis of semiempirical MNDO molecular orbital calculations 7 and has since been confirmed in many ab initio studies. 8 ᎐ 12 It has been suggested that this extensive delocalization of the nitrogen charge is responsible for the unexpectedly small destabilizing effect of the highly electron-withdrawing COCH group in aryl nitrenium ions of the type 3 …”

Singlet and triplet states in the reactions of nitrenium ions

“…In contrast, the singlet possesses a planar structure and a shortened C-N bond (1.311 Å ) consistent with its cyclohexadienyl imine cation character. This finding holds true at all levels of theory starting with AM1 semiempirical calculations 11,[37][38][39] all the way up to DFT calculations (BVWN5/cc-pVTZ//BVWN5/ccpVDZ). 40 Apparently the triplet behaves as a protonated triplet nitrene.…”

Selective arylation of exocyclicN-position of 2-pyrimidylnitrenium ion photolytically generated from tetrazolo-[1,5-a]pyrimidine in the presence of trifluoroacetic acid

“…7 By the replacement of the phenyl ring of the nitrenium ion with a pyrimidyl ring, the positive charge can be preferentially localized on its exocyclic N-position since the positive charge unfavourably populates the pyrimidyl ring compared with the phenyl ring owing to a higher electronegativity of an N atom compared with a C atom. This may explain the reason why the singlet pyrimidylnitrenium ion is more electrophilic for the arylation than the singlet phenylnitrenium ion, and undergoes the selective exocyclic N-arylation in spite of N-and C-arylations 3 of the latter ion.…”