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σ‐Resonance Stabilization of Aminomethylene by N‐Halogenation.

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Title: σ‐Resonance Stabilization of Aminomethylene by N‐Halogenation.
Authors: Medvedko, Serhii1 (AUTHOR), Bhagat, Virinder2 (AUTHOR), Wagner, J. Philipp1 (AUTHOR) jpw@uni‐bremen.de
Source: Journal of Computational Chemistry. 3/30/2026, Vol. 47 Issue 8, p1-6. 6p.
Subjects: Halogenation, Resonance effect, Carbenes, Computational chemistry, Carbene synthesis, Electronic structure, Pyridine
Abstract: Amino substitution effectively stabilizes carbenes via π‐resonance, enabling their isolation as N‐heterocyclic carbenes (NHCs). Our group has recently demonstrated that N‐halogenation of pyridinylidenes (Hammick intermediates) provides an additional stabilization mode through a rarely utilized σ‐resonance. However, this σ‐resonance interaction might not yet have reached its full potential due to the constriction of the carbene motif within a cyclic structure. Thus, we have studied the impact of N‐halogenation (X = Br, I) on the structure, energetics, and spectroscopic properties of the parent open‐chain aminocarbene, aminomethylene, utilizing fully unconstrained CCSD(T) and NEVPT2 geometry optimizations together with a def2‐TZVPP basis set. We find that the halogenated carbenes prefer a Z configuration of the C–N bond, which is impossible in a cyclic arrangement. Halogenated aminomethylenes are kinetically protected against unimolecular rearrangement by barriers exceeding 35 kcal mol−1. Short C–N bond lengths (1.23 Å) and wide carbene angles (~125°) indicate cooperative π‐ and σ‐resonance stabilization, resulting in carbene stabilization energies (CSEs) increased by ~12–13 kcal mol−1 relative to the parent aminomethylene. The electronic structure is characterized by the σ* orbital of the N–X bond as the lowest unoccupied molecular orbital. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Computational Chemistry is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: σ‐Resonance Stabilization of Aminomethylene by N‐Halogenation.
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  Data: <searchLink fieldCode="AR" term="%22Medvedko%2C+Serhii%22">Medvedko, Serhii</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Bhagat%2C+Virinder%22">Bhagat, Virinder</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Wagner%2C+J%2E+Philipp%22">Wagner, J. Philipp</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> jpw@uni‐bremen.de</i>
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Computational+Chemistry%22">Journal of Computational Chemistry</searchLink>. 3/30/2026, Vol. 47 Issue 8, p1-6. 6p.
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  Data: <searchLink fieldCode="DE" term="%22Halogenation%22">Halogenation</searchLink><br /><searchLink fieldCode="DE" term="%22Resonance+effect%22">Resonance effect</searchLink><br /><searchLink fieldCode="DE" term="%22Carbenes%22">Carbenes</searchLink><br /><searchLink fieldCode="DE" term="%22Computational+chemistry%22">Computational chemistry</searchLink><br /><searchLink fieldCode="DE" term="%22Carbene+synthesis%22">Carbene synthesis</searchLink><br /><searchLink fieldCode="DE" term="%22Electronic+structure%22">Electronic structure</searchLink><br /><searchLink fieldCode="DE" term="%22Pyridine%22">Pyridine</searchLink>
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  Data: Amino substitution effectively stabilizes carbenes via π‐resonance, enabling their isolation as N‐heterocyclic carbenes (NHCs). Our group has recently demonstrated that N‐halogenation of pyridinylidenes (Hammick intermediates) provides an additional stabilization mode through a rarely utilized σ‐resonance. However, this σ‐resonance interaction might not yet have reached its full potential due to the constriction of the carbene motif within a cyclic structure. Thus, we have studied the impact of N‐halogenation (X = Br, I) on the structure, energetics, and spectroscopic properties of the parent open‐chain aminocarbene, aminomethylene, utilizing fully unconstrained CCSD(T) and NEVPT2 geometry optimizations together with a def2‐TZVPP basis set. We find that the halogenated carbenes prefer a Z configuration of the C–N bond, which is impossible in a cyclic arrangement. Halogenated aminomethylenes are kinetically protected against unimolecular rearrangement by barriers exceeding 35 kcal mol−1. Short C–N bond lengths (1.23 Å) and wide carbene angles (~125°) indicate cooperative π‐ and σ‐resonance stabilization, resulting in carbene stabilization energies (CSEs) increased by ~12–13 kcal mol−1 relative to the parent aminomethylene. The electronic structure is characterized by the σ* orbital of the N–X bond as the lowest unoccupied molecular orbital. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of Journal of Computational Chemistry is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1002/jcc.70360
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      – Code: eng
        Text: English
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      – SubjectFull: Halogenation
        Type: general
      – SubjectFull: Resonance effect
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      – SubjectFull: Carbenes
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      – SubjectFull: Carbene synthesis
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      – SubjectFull: Electronic structure
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      – SubjectFull: Pyridine
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      – TitleFull: σ‐Resonance Stabilization of Aminomethylene by N‐Halogenation.
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            NameFull: Bhagat, Virinder
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              Text: 3/30/2026
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              Y: 2026
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