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Proton transfers in hydrogen‐bonded systems V. Analysis of electronic redistributions in (N 2 H 7 ) +
Author(s) -
Scheiner Steve
Publication year - 1981
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560200719
Subject(s) - chemistry , atomic orbital , lone pair , atomic physics , proton , basis set , molecular orbital , molecular physics , ab initio , molecule , density functional theory , electron , computational chemistry , physics , quantum mechanics , organic chemistry
The transfer of the central proton between the two NH 3 units of (H 3 NHNH 3 ) + is studied using the 4–31 G basis set within the ab‐initio Hartree‐Fock formalism. Electron density difference maps are constructed which clearly indicate electronic redistributions which accompany the half‐transfer of the proton from its equilibrium position (NHN) to the midpoint of the hydrogen bond (NHN). The overall loss of electronic charge from the proton‐accepting molecule originates in three distinct regions of space, while a density buildup of smaller magnitude is observed in a characteristic region centered about the N nucleus. Similar regions are noted for the proton‐donating molecule, although the changes are reversed in sign. A partitioning of the total density changes into contributions from the various molecular orbitals demonstrates that the a 1 orbitals are associated with density shifts along the H‐bond axis. Changes in the N lone pairs are attributed chiefly to the (5a 1 ,6a 1 ) pair and are somewhat attenuated by opposite shifts involving the (3a 1 . 4a 1 ) pair. Orbitals of e symmetry lead to polarizations of the NH bonds and density shifts perpendicular to the H‐bond axis.