Variation of Nucleophilicity NHnA of Atoms A in Hydrides HnA with the Group and Row of A in the Periodic Table.

Abstract

Nucleophilicities N_HnA of hydrides of atoms A acting as hydrogen-bond acceptors in complexes H_nA···HX are reported. The H_nA initially chosen are HB, H₂C, H₃N, H₂O, and HF, that is from groups 13, 14, 15, 16, and 17, respectively, of row 1 of the Periodic Table. The Lewis acids HX involved are HF, HCl, HBr, HI, HCCH, and HCP. Nucleophilicities are determined from dissociation energies D_e for the process H_nA···HX = H_nA + HX by using D_e = cN_HnA.E_HX, where E_HX are electrophilicities of the Lewis acids HX. This procedure is also followed for hydrides H_nA in which the atoms A are from the same groups, but from rows 2, 3, and 4 of the Periodic Table. The order of N_HnA values found is row 1 > row 2 ≈ row 3 ≈ row 4 in each of groups 13, 15, 15, 16, and 17, with a large decrease from row 1 to row 2 but with small decreases from rows 2 to 3 to 4. The series Rg···HX is similarly investigated to give the order of nucleophilicities Rg = Xe > Kr > Ar. > Ne, which is reversed from that in the hydrides of groups 13 to 17.