Generalized Anomeric Effect on <i>N-</i>Alkyl-amino Cation Affinities: A G2(+)_M Investigation

The gas-phase <i>N</i>-alkyl-amino-cation affinities (NAACA) of archetypal anionic main-group element hydrides across the Periodic Table have been investigated by means of a modified G2­(+) scheme. The reactions studied include R₂NB → R₂N⁺ + B^– (R = H, Me; B = XH_<i>n</i>, <i>n</i> = 0–3; X = F, Cl, Br, O, S, Se, N, P, As, C, Si, Ge). Our calculations indicate that the reasonable linear correlations between NAACA and proton affinities (PA) only exist within the Period 2 anions, including H₃C^–, H₂N^–, HO^–, and F^–, or the anions within Periods 3–4 in the Periodic Table, which is significantly different from the alkyl cation affinities, where there is a reasonable correlation between the computed alkyl cation affinity and PA values of the set of anionic main-group element hydrides. The interesting differences can be ascribed to the generalized anomeric effect induced by <i>n</i>(N) → σ*­(X–H) negative hyperconjugation found in R₂NXH_<i>n</i>, with central atom X belonging to Groups 14–16 (X = O, S, Se, N, P, As, C, Si, Ge)