DFT-GIAO and DFT-NBO studies of the origin of 19F NMR shielding effects in alkyl fluorides

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Electron delocalization into the local environment of the fluorine nucleus in the anti (1) and syn (2) epimers of 7-norbornenyl fluoride, 7-fluoronorbornane (3), 7-fluoronobornadiene (4) and the equatorial and axial epimers of cyclohexyl fluoride (5 and 6, respectively) were studied using the natura...

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Autores principales: Peralta, Juan Ernesto, Contreras, Rubén Horacio
Publicado: 1999
Materias:
7-norbornenyl fluorides
19F chemical shifts
19F NMR
1J(C,F)F and 2J(C,F) couplings
Cyclohexyl fluorides
DFT-GIAO
DFT-NBO
NMR
Acceso en línea:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_07491581_v37_n3_p167_Adcock
http://hdl.handle.net/20.500.12110/paper_07491581_v37_n3_p167_Adcock
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
id paper:paper_07491581_v37_n3_p167_Adcock
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spelling paper:paper_07491581_v37_n3_p167_Adcock2025-07-30T18:22:01Z DFT-GIAO and DFT-NBO studies of the origin of 19F NMR shielding effects in alkyl fluorides Peralta, Juan Ernesto Contreras, Rubén Horacio 7-norbornenyl fluorides 19F chemical shifts 19F NMR 1J(C,F)F and 2J(C,F) couplings Cyclohexyl fluorides DFT-GIAO DFT-NBO NMR Electron delocalization into the local environment of the fluorine nucleus in the anti (1) and syn (2) epimers of 7-norbornenyl fluoride, 7-fluoronorbornane (3), 7-fluoronobornadiene (4) and the equatorial and axial epimers of cyclohexyl fluoride (5 and 6, respectively) were studied using the natural bond orbital (NBO) approach. The level of theory, B3LYP/6-311G**, was chosen in such a way that the GIAO-calculated 19F magnetic shielding constants in all these compounds were in very good agreement with experimental values. The large 19F deshielding effects known experimentally in 1 and 4 with respect to 2 and 3 are rationalized in terms of differences in such electron delocalizations. The main contribution is that corresponding to the π → (C-F)* interaction, which is only efficient for an anti orientation of the C-F bond and the vinyl moiety. 19F and 13C NMR spectra of 5 and 6 were also measured because some ambiguity was detected in the literature. Despite the large calculated charge donation to the fluorine environment in 6, its 19F resonance appears upfield from that in 5. This trend is rationalized as originating in γ effects of the C-Hax bonds of the kind which have been invoked to explain 17O chemical shift trends in different cyclohexanols and their respective ethers. Electron delocalization effects on 1J(C,F) and 2J(C,F) couplings are also discussed. Copyright © 1999 John Wiley & Sons, Ltd. Fil:Peralta, J.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Contreras, R.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. 1999 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_07491581_v37_n3_p167_Adcock http://hdl.handle.net/20.500.12110/paper_07491581_v37_n3_p167_Adcock
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic 7-norbornenyl fluorides
19F chemical shifts
19F NMR
1J(C,F)F and 2J(C,F) couplings
Cyclohexyl fluorides
DFT-GIAO
DFT-NBO
NMR
spellingShingle 7-norbornenyl fluorides
19F chemical shifts
19F NMR
1J(C,F)F and 2J(C,F) couplings
Cyclohexyl fluorides
DFT-GIAO
DFT-NBO
NMR
Peralta, Juan Ernesto
Contreras, Rubén Horacio
DFT-GIAO and DFT-NBO studies of the origin of 19F NMR shielding effects in alkyl fluorides
topic_facet 7-norbornenyl fluorides
19F chemical shifts
19F NMR
1J(C,F)F and 2J(C,F) couplings
Cyclohexyl fluorides
DFT-GIAO
DFT-NBO
NMR
description Electron delocalization into the local environment of the fluorine nucleus in the anti (1) and syn (2) epimers of 7-norbornenyl fluoride, 7-fluoronorbornane (3), 7-fluoronobornadiene (4) and the equatorial and axial epimers of cyclohexyl fluoride (5 and 6, respectively) were studied using the natural bond orbital (NBO) approach. The level of theory, B3LYP/6-311G**, was chosen in such a way that the GIAO-calculated 19F magnetic shielding constants in all these compounds were in very good agreement with experimental values. The large 19F deshielding effects known experimentally in 1 and 4 with respect to 2 and 3 are rationalized in terms of differences in such electron delocalizations. The main contribution is that corresponding to the π → (C-F)* interaction, which is only efficient for an anti orientation of the C-F bond and the vinyl moiety. 19F and 13C NMR spectra of 5 and 6 were also measured because some ambiguity was detected in the literature. Despite the large calculated charge donation to the fluorine environment in 6, its 19F resonance appears upfield from that in 5. This trend is rationalized as originating in γ effects of the C-Hax bonds of the kind which have been invoked to explain 17O chemical shift trends in different cyclohexanols and their respective ethers. Electron delocalization effects on 1J(C,F) and 2J(C,F) couplings are also discussed. Copyright © 1999 John Wiley & Sons, Ltd.
author Peralta, Juan Ernesto
Contreras, Rubén Horacio
author_facet Peralta, Juan Ernesto
Contreras, Rubén Horacio
author_sort Peralta, Juan Ernesto
title DFT-GIAO and DFT-NBO studies of the origin of 19F NMR shielding effects in alkyl fluorides
title_short DFT-GIAO and DFT-NBO studies of the origin of 19F NMR shielding effects in alkyl fluorides
title_full DFT-GIAO and DFT-NBO studies of the origin of 19F NMR shielding effects in alkyl fluorides
title_fullStr DFT-GIAO and DFT-NBO studies of the origin of 19F NMR shielding effects in alkyl fluorides
title_full_unstemmed DFT-GIAO and DFT-NBO studies of the origin of 19F NMR shielding effects in alkyl fluorides
title_sort dft-giao and dft-nbo studies of the origin of 19f nmr shielding effects in alkyl fluorides
publishDate 1999
url https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_07491581_v37_n3_p167_Adcock
http://hdl.handle.net/20.500.12110/paper_07491581_v37_n3_p167_Adcock
work_keys_str_mv AT peraltajuanernesto dftgiaoanddftnbostudiesoftheoriginof19fnmrshieldingeffectsinalkylfluorides
AT contrerasrubenhoracio dftgiaoanddftnbostudiesoftheoriginof19fnmrshieldingeffectsinalkylfluorides
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