TOUŠEK, Jaromír, Michal STRAKA, Vladimír SKLENÁŘ and Radek MAREK. Origin of the Conformational Modulation of the 13C NMR Chemical Shift of Methoxy Groups in Aromatic Natural Compounds. The Journal of Physical Chemistry A. American Chemical Society, 2013, vol. 117, No 3, p. 661-669. ISSN 1089-5639. doi:10.1021/jp310470f.
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Basic information
Original name Origin of the Conformational Modulation of the 13C NMR Chemical Shift of Methoxy Groups in Aromatic Natural Compounds
Authors TOUŠEK, Jaromír (203 Czech Republic, belonging to the institution), Michal STRAKA (203 Czech Republic, belonging to the institution), Vladimír SKLENÁŘ (203 Czech Republic, belonging to the institution) and Radek MAREK (203 Czech Republic, guarantor, belonging to the institution).
Edition The Journal of Physical Chemistry A, American Chemical Society, 2013, 1089-5639.
Other information
Original language English
Type of outcome Article in a journal
Field of Study 10403 Physical chemistry
Country of publisher United States of America
Confidentiality degree is not subject to a state or trade secret
WWW DOI: 10.1021/jp310470f
Impact factor Impact factor: 2.775
RIV identification code RIV/00216224:14740/13:00067650
Organization unit Central European Institute of Technology
Doi http://dx.doi.org/10.1021/jp310470f
UT WoS 000314205300015
Keywords in English Nuclear magnetic schielding; DFT calculations; molecular orbitals; excitation analysis; orbital rotation model
Tags rivok
Tags International impact, Reviewed
Changed by Changed by: Olga Křížová, učo 56639. Changed: 12. 1. 2015 08:30.
Abstract
The interpretation of nuclear magnetic resonance (NMR) parameters is essential to understanding experimental observations at the molecular and supramolecular levels and to designing new and more efficient molecular probes. In many aromatic natural compounds, unusual 13C NMR chemical shifts have been reported for out-of-plane methoxy groups bonded to the aromatic ring (~62 ppm as compared to the typical value of ~56 ppm for an aromatic methoxy group). Here, we analyzed this phenomenon for a series of aromatic natural compounds using Density Functional Theory (DFT) calculations. First, we checked the methodology used to optimize the structure and calculate the NMR chemical shifts in aromatic compounds. The conformational effects of the methoxy group on the 13C NMR chemical shift then were interpreted by the Natural Bond Orbital (NBO) and Natural Chemical Shift (NCS) approaches, and by excitation analysis of the chemical shifts, breaking down the total nuclear shielding tensor into the contributions from the different occupied orbitals and their magnetic interactions with virtual orbitals. We discovered that the atypical 13C NMR chemical shifts observed are not directly related to a different conjugation of the lone pair of electrons of the methoxy oxygen with the aromatic ring, as has been suggested. Our analysis indicates that rotation of the methoxy group induces changes in the virtual molecular orbital space, which, in turn, correlate with the predominant part of the contribution of the paramagnetic deshielding connected with the magnetic interactions of the BD(CMet–H)---BD*(CMet–OMet) orbitals, resulting in the experimentally observed deshielding of the 13C NMR resonance of the out-of-plane methoxy group.
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ED1.1.00/02.0068, research and development projectName: CEITEC - central european institute of technology
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