Experimental and theoretical study of hyperconjugative interaction effects on NMR1JCH scalar couplings
Hyperconjugative and electrostatic interactions effects on 1JCH spin-spin coupling constants (SSCCs) are critically studied from both theoretical and experimental points of view. A qualitative model is used to predict how the former affect such SSCCs, while electrostatic interactions are modeled wit...
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| Autores principales: | , , , , , , |
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| Formato: | JOUR |
| Materias: | |
| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_10895639_v110_n12_p4266_Contreras |
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| Sumario: | Hyperconjugative and electrostatic interactions effects on 1JCH spin-spin coupling constants (SSCCs) are critically studied from both theoretical and experimental points of view. A qualitative model is used to predict how the former affect such SSCCs, while electrostatic interactions are modeled with a point charge placed in the vicinity of the corresponding σCH bond. Hyperconjugative interactions are calculated using the "natural bond orbital" approach, and using the point-charge model, it is shown how intertwined are both types of interactions. Several members of the series 1-X-bicyclo[1.1.1]pentane and 1-X-3- methylbicyclo[1.1.1]pentane are chosen as model compounds for measuring 1JCH SSCCs; in some of them were performed also DFT-SSCC calculations. The strained cage substrate in these series defines strong σ-hyperconjugative interactions, making these compounds excellent examples to verify the qualitative model presented in this work. It is verified that (a) hyperconjugative interactions from the σCH bond or into the σ*CH antibond containing the coupling nuclei yield a decrease of the corresponding 1JCH SSCC and (b) hyperconjugative interactions from other bonds involving the coupling C nucleus yield an increase of that 1JCH SSCC. © 2006 American Chemical Society. |
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