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Torsional Barriers Resulting from Two‐electron and Four‐electron Interactions. The Hydrazyl Cation and Anion Models
Author(s) -
Kost D.,
Aviram K.,
Raban M.
Publication year - 1983
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198300017
Subject(s) - chemistry , ion , electron , computational chemistry , crystallography , molecular orbital , molecule , organic chemistry , physics , quantum mechanics
The spectrum of rotations about single bonds has been divided into two different groups of processes, termed T A and T C . These describe interconversion of planar ground state conformations (as in amides), and interconversion of enantiomers (as in sulfenamides and hydroxylamines), respectively. A frontier molecular orbital analysis of the hydrazyl cation and anion reveals that a change in electron occupancy alone can bring about a change from one torsional process to the other. Thus, the four‐electron hydrazyl anion undergoes a T C process, while the corresponding two‐electron cation undergoes a T A rotation. Nonempirical SCF‐MO calculations of the model cation and anion with geometry optimization at the 4‐31G level confirm the results of the PMO analysis. The calculations also reveal a preference for an inversion (I A ) mechanism for the topomerization of the cation system over a torsional process.