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Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
Aromaticity and relative stabilities of azines
Yan Wang1, Judy I-Chia Wu, Qianshu Li
1School of Science, Beijing Institute of Technology, Beijing 100081, China.
Organic Letters
|October 12, 2010
Summary
Azines and aza-naphthalenes exhibit aromaticity comparable to benzene and naphthalene, respectively. Lower energies in isomers with adjacent nitrogens stem from weak N-N bonds, not diminished aromaticity.
Area of Science:
- Computational Chemistry
- Organic Chemistry
- Quantum Chemistry
Background:
- Aromaticity is a key concept in understanding the stability and reactivity of cyclic organic molecules.
- Azines and aza-naphthalenes are nitrogen-containing heterocyclic analogues of benzene and naphthalene.
- Quantifying the aromaticity of these heterocycles is crucial for predicting their chemical behavior.
Purpose of the Study:
- To quantitatively assess and compare the aromaticity of various azines and aza-naphthalenes.
- To investigate the factors contributing to the relative energies of isomers with vicinal nitrogen atoms.
- To establish a benchmark for aromaticity in nitrogen-containing aromatic systems.
Main Methods:
- Utilizing the block localized wave function (BLW) method for electronic structure calculations.
- Employing nucleus-independent chemical shift (NICS(0)(πzz)) as a primary index for aromaticity.
- Calculating extra cyclic resonance energies (ECREs) to further evaluate aromatic stabilization.
Main Results:
- The NICS(0)(πzz) and ECREs indicate that azines possess aromaticity similar to benzene.
- Aza-naphthalenes demonstrate aromaticity comparable to naphthalene.
- Isomers featuring vicinal nitrogen atoms exhibit lower relative energies due to weak N-N bonds, not reduced aromaticity.
Conclusions:
- Azines and aza-naphthalenes are aromatic systems with stability comparable to their carbocyclic counterparts.
- The presence and position of nitrogen atoms do not fundamentally alter the aromatic character.
- The energetic preference for certain isomers is governed by sigma bond strengths rather than pi system aromaticity.
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