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Methyl β‐substituent effect on NMR 17 O chemical shifts in two‐coordinated oxygen atoms: DFT GIAO and NBO and experimental studies
Author(s) -
Peralta J. E.,
Contreras R. H.,
Taurian O. E.,
Ortiz F. S.,
de Kowalewski D. G.,
Kowalewski V. J.
Publication year - 1999
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199901)37:1<31::aid-mrc396>3.0.co;2-e
Subject(s) - natural bond orbital , chemistry , substituent , intramolecular force , chemical shift , atomic orbital , computational chemistry , oxygen , oxygen atom , charge (physics) , crystallography , density functional theory , stereochemistry , molecule , electron , organic chemistry , physics , quantum mechanics
Methyl β‐substituent effects on 17 O chemical shifts in dicoordinated oxygen atoms in compounds ofthe type CH 3 OX are found to be insensitiveto the nature of the X substrate, even for strongly conjugatinggroups. Such behavior is rationalized in terms of intramolecularelectron delocalizing using the natural bond orbitals approach tocalculate NBO E (2) charge‐transferenergies. The level of theory employed in this analysis was chosen insuch a way that DFT GIAO at the same level could describe theexperimental trends adequately. In this way, it was found that chargetransfers to (OC)* antibonds render importantdeshielding effects on the 17 O chemical shifts. In theparticular case of the methyl β‐substituent effect quotedabove, such charge transfer originates in the preferentialorientation that the C α H 2 —C β H 3 group adopts in these compounds CH 3 OX. Analogies with 19 F chemicalshifts are discussed. © 1999 John Wiley & Sons, Ltd.