Stereoelectronic contributions to long-range 1H-1H coupling constants

The contribution of stereoelectronic interactions to NMR coupling constants 3JHH and 4JHH has been examined using ab initio calculations and natural bond orbital (NBO) analysis on four model compounds: ethane, propane, propene, and methylcyclopropane. The main stereoelectronic contributions to the c...

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Autores principales: Sproviero, Eduardo Marcelo, Burton, Gerardo
Publicado: 2002
Materias:
Natural bond orbital (NBO) analysis
Stereoelectronic interactions
Hydrogen bonds
Molecular structure
Nuclear magnetic resonance spectroscopy
Polarization
Protons
Hydrocarbons
Acceso en línea:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10895639_v106_n34_p7834_Sproviero
http://hdl.handle.net/20.500.12110/paper_10895639_v106_n34_p7834_Sproviero
Aporte de:
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
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spelling paper:paper_10895639_v106_n34_p7834_Sproviero2023-06-08T16:06:17Z Stereoelectronic contributions to long-range 1H-1H coupling constants Sproviero, Eduardo Marcelo Burton, Gerardo Natural bond orbital (NBO) analysis Stereoelectronic interactions Hydrogen bonds Molecular structure Nuclear magnetic resonance spectroscopy Polarization Protons Hydrocarbons The contribution of stereoelectronic interactions to NMR coupling constants 3JHH and 4JHH has been examined using ab initio calculations and natural bond orbital (NBO) analysis on four model compounds: ethane, propane, propene, and methylcyclopropane. The main stereoelectronic contributions to the couplings originate in three-bond (vicinal) interactions and in through-space interactions. In ethane, besides the main contribution of the σ(C-H) → σ*(C-H) interaction, other interactions present in the molecule make a decisive contribution to the angular dependence of 3J. In the H1-C-C-C-Hanti moiety of propane, 4JHH has important contributions from vicinal interactions that include the anti proton while in the H1-C-C-C-Hgauche moiety the main contributions are vicinal interactions that include H1. In alkene fragments, vicinal interactions that involve the π orbitals are the most important contributions to the couplings. Sigma vicinal interactions, which include orbitals corresponding to C-H bonds that involve either of the coupled protons, are crucial to elucidate differences between cisoid and transoid coupling constants. In the case of methylcyclopropane, the most important contributions to the coupling of the syn cyclopropyl H come from the σ(C-H) → σ*(Ccyclopropane-Ccyclopropane) and σ(Ccyclopropane-Ccyclopropane) → σ*(C-H) vicinal interactions (where the H corresponds to the non-cyclopropyl hydrogen). The concerted effect of several interactions that contribute toward a trend similar to that shown by allyl-vinyl proton couplings is in accordance with a significant π contribution of the Ccyclopropane-Ccyclopropane bond. For the anti cyclopropyl proton, vicinal interactions of the form σ(C-Hanti) → σ*(Ccyclopropane-C) and σ(Ccyclopropane-C) → σ*(C-Hanti) are the main contributors to the angular variation of the couplings, similar to what happens to the anti proton in propane. As a whole, the overall behavior of these couplings resembles that of the equivalent proton in propane. In addition, in this case there is not a unique set of interactions which accounts for the overall angular variation of 4J. Fil:Sproviero, E.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Burton, G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. 2002 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10895639_v106_n34_p7834_Sproviero http://hdl.handle.net/20.500.12110/paper_10895639_v106_n34_p7834_Sproviero
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic Natural bond orbital (NBO) analysis
Stereoelectronic interactions
Hydrogen bonds
Molecular structure
Nuclear magnetic resonance spectroscopy
Polarization
Protons
Hydrocarbons
spellingShingle Natural bond orbital (NBO) analysis
Stereoelectronic interactions
Hydrogen bonds
Molecular structure
Nuclear magnetic resonance spectroscopy
Polarization
Protons
Hydrocarbons
Sproviero, Eduardo Marcelo
Burton, Gerardo
Stereoelectronic contributions to long-range 1H-1H coupling constants
topic_facet Natural bond orbital (NBO) analysis
Stereoelectronic interactions
Hydrogen bonds
Molecular structure
Nuclear magnetic resonance spectroscopy
Polarization
Protons
Hydrocarbons
description The contribution of stereoelectronic interactions to NMR coupling constants 3JHH and 4JHH has been examined using ab initio calculations and natural bond orbital (NBO) analysis on four model compounds: ethane, propane, propene, and methylcyclopropane. The main stereoelectronic contributions to the couplings originate in three-bond (vicinal) interactions and in through-space interactions. In ethane, besides the main contribution of the σ(C-H) → σ*(C-H) interaction, other interactions present in the molecule make a decisive contribution to the angular dependence of 3J. In the H1-C-C-C-Hanti moiety of propane, 4JHH has important contributions from vicinal interactions that include the anti proton while in the H1-C-C-C-Hgauche moiety the main contributions are vicinal interactions that include H1. In alkene fragments, vicinal interactions that involve the π orbitals are the most important contributions to the couplings. Sigma vicinal interactions, which include orbitals corresponding to C-H bonds that involve either of the coupled protons, are crucial to elucidate differences between cisoid and transoid coupling constants. In the case of methylcyclopropane, the most important contributions to the coupling of the syn cyclopropyl H come from the σ(C-H) → σ*(Ccyclopropane-Ccyclopropane) and σ(Ccyclopropane-Ccyclopropane) → σ*(C-H) vicinal interactions (where the H corresponds to the non-cyclopropyl hydrogen). The concerted effect of several interactions that contribute toward a trend similar to that shown by allyl-vinyl proton couplings is in accordance with a significant π contribution of the Ccyclopropane-Ccyclopropane bond. For the anti cyclopropyl proton, vicinal interactions of the form σ(C-Hanti) → σ*(Ccyclopropane-C) and σ(Ccyclopropane-C) → σ*(C-Hanti) are the main contributors to the angular variation of the couplings, similar to what happens to the anti proton in propane. As a whole, the overall behavior of these couplings resembles that of the equivalent proton in propane. In addition, in this case there is not a unique set of interactions which accounts for the overall angular variation of 4J.
author Sproviero, Eduardo Marcelo
Burton, Gerardo
author_facet Sproviero, Eduardo Marcelo
Burton, Gerardo
author_sort Sproviero, Eduardo Marcelo
title Stereoelectronic contributions to long-range 1H-1H coupling constants
title_short Stereoelectronic contributions to long-range 1H-1H coupling constants
title_full Stereoelectronic contributions to long-range 1H-1H coupling constants
title_fullStr Stereoelectronic contributions to long-range 1H-1H coupling constants
title_full_unstemmed Stereoelectronic contributions to long-range 1H-1H coupling constants
title_sort stereoelectronic contributions to long-range 1h-1h coupling constants
publishDate 2002
url https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10895639_v106_n34_p7834_Sproviero
http://hdl.handle.net/20.500.12110/paper_10895639_v106_n34_p7834_Sproviero
work_keys_str_mv AT sprovieroeduardomarcelo stereoelectroniccontributionstolongrange1h1hcouplingconstants
AT burtongerardo stereoelectroniccontributionstolongrange1h1hcouplingconstants
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