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Published on: July 27, 2022
Interconversion Mechanisms in H2N-O-NH2: Rotamerism, Pyramidal Inversion, or Akamptisomerism?
1Department of Chemistry, Institute of Natural Sciences, Federal University of Lavras, 37200-900, Lavras, MG, Brazil.
The Journal of Physical Chemistry. A
|June 27, 2026
Summary
Akamptisomerism, a rare bond-angle inversion, is not a viable process in simple X-O-X systems. This molecular behavior requires specific constraints, unlike common rotamerism or pyramidal inversion.
Area of Science:
- Computational Chemistry
- Molecular Modeling
- Organic Chemistry
Background:
- Conformational isomerism is key to molecular behavior.
- Akamptisomerism (bond-angle inversion) is poorly understood and rarely observed.
- Existing evidence for akamptisomerism is mainly in B-O-B-bridged macrocycles.
Purpose of the Study:
- To investigate the conformational landscapes of X-O-X systems (X = B, C, N, O).
- To assess the generality of akamptisomerism as a molecular inversion mechanism.
- To compare akamptisomerism with other inversion pathways like rotamerism and pyramidal inversion.
Main Methods:
- Computational searches for conformational landscapes.
- Calculation of energy profiles using GFN2-xTB and B3LYP/def2-TZVP methods.
- Analysis of potential energy surfaces to identify transition states and reaction pathways.
Main Results:
- Akamptisomerism was found to be non-viable in simple X-O-X systems.
- Linear geometries represent high-order saddle points, not true transition states.
- Prohibitive energy costs (over 70 kcal mol⁻¹) were associated with attempted akamptisomerism.
- H₂N-O-NH₂ interconverts via rotamerism (∼15 kcal mol⁻¹) and trigonal pyramidal inversion (∼8 kcal mol⁻¹).
Conclusions:
- Akamptisomerism is not a general feature of X-O-X molecular motifs.
- This inversion mechanism likely requires specific geometric constraints, such as those in macrocyclic structures.
- Trigonal pyramidal inversion is a more favorable pathway for H₂N-O-NH₂ compared to akamptisomerism.
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