Why do two π-electron four-membered Hückel rings pucker?
Notwithstanding their two (i.e., 4n + 2) π electrons, four-membered ring systems, 1-4, favor puckered geometries (1a-4a) despite the reduction in vicinal π overlap and in the ring atom bond angles. This nonplanar preference is due to σ → π* hyperconjugative interactions across the ring (A) rather th...
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| Main Authors: | , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
8 November 2012
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| In: |
Organic letters
Year: 2012, Volume: 14, Issue: 22, Pages: 5712-5715 |
| ISSN: | 1523-7052 |
| DOI: | 10.1021/ol302726c |
| Online Access: | Verlag, Volltext: http://dx.doi.org/10.1021/ol302726c Verlag, Volltext: https://doi.org/10.1021/ol302726c 
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| Author Notes: | William C. McKee, Judy I. Wu, Matthias Hofmann, Armin Berndt, and Paul von Ragué Schleyer |
| Summary: | Notwithstanding their two (i.e., 4n + 2) π electrons, four-membered ring systems, 1-4, favor puckered geometries (1a-4a) despite the reduction in vicinal π overlap and in the ring atom bond angles. This nonplanar preference is due to σ → π* hyperconjugative interactions across the ring (A) rather than to partial 1,3-bonding (B). Electronegative substituents (e.g., F in C4F42+) reduce the σ → π* electron delocalization, and planar geometries result. In contrast, electropositive groups (e.g., SiH3 in C4(SiH3)42+) enhance hyperconjugation and increase the ring inversion barriers substantially. |
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| Item Description: | Gesehen am 15.11.2018 |
| Physical Description: | Online Resource |
| ISSN: | 1523-7052 |
| DOI: | 10.1021/ol302726c |