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Can Variations of (HNMR)-H-1 Chemical Shifts in Benzene Substituted with an Electron-Accepting (NO2)/Donating (NH2) Group be Explained in Terms of Resonance Effects of Substituents?

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2018
Authors
Baranac-Stojanović, Marija
Article (Published version)
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Abstract
The classical textbook explanation of variations of (HNMR)-H-1 chemical shifts in benzenes bearing an electron-donating (NH2) or an electron-withdrawing (NO2) group in terms of substituent resonance effects was examined by analyzing molecular orbital contributions to the total shielding. It was found that the -electronic system showed a more pronounced shielding effect on all ring hydrogen atoms, relative to benzene, irrespective of substituent +R/-R effects. For the latter, this was in contrast to the traditional explanations of downfield shift of nitrobenzene proton resonances, which were found to be determined by the sigma-electronic system and oxygen in-plane lone pairs. In aniline, the +R effect of NH2 group can be used to fully explain the upfield position of meta-H signals and partly the upfield position of para-H signals, the latter also being influenced by the sigma-system. The position of the lowest frequency signal of ortho-Hs was fully determined by sigma-electrons.
Keywords:
benzene / density functional calculations / NMR spectroscopy / proton chemical shifts / substituent effects
Source:
Chemistry. An Asian Journal, 2018, 13, 7, 877-881
Publisher:
  • Wiley-V C H Verlag Gmbh, Weinheim
Funding / projects:
  • Experimental and theoretical study of reactivity and biological activity of stereodefined thiazolidines and their synthetic analogues (RS-172020)
Note:
  • Peer-reviewed manuscript: http://cherry.chem.bg.ac.rs/handle/123456789/3180
  • Supplementary material: http://cherry.chem.bg.ac.rs/handle/123456789/3181

DOI: 10.1002/asia.201800137

ISSN: 1861-4728

PubMed: 29509309

WoS: 000429415400022

Scopus: 2-s2.0-85043272617
[ Google Scholar ]
1
1
URI
https://cherry.chem.bg.ac.rs/handle/123456789/2127
Collections
  • Publikacije
Institution/Community
Hemijski fakultet
TY  - JOUR
AU  - Baranac-Stojanović, Marija
PY  - 2018
UR  - https://cherry.chem.bg.ac.rs/handle/123456789/2127
AB  - The classical textbook explanation of variations of (HNMR)-H-1 chemical shifts in benzenes bearing an electron-donating (NH2) or an electron-withdrawing (NO2) group in terms of substituent resonance effects was examined by analyzing molecular orbital contributions to the total shielding. It was found that the -electronic system showed a more pronounced shielding effect on all ring hydrogen atoms, relative to benzene, irrespective of substituent +R/-R effects. For the latter, this was in contrast to the traditional explanations of downfield shift of nitrobenzene proton resonances, which were found to be determined by the sigma-electronic system and oxygen in-plane lone pairs. In aniline, the +R effect of NH2 group can be used to fully explain the upfield position of meta-H signals and partly the upfield position of para-H signals, the latter also being influenced by the sigma-system. The position of the lowest frequency signal of ortho-Hs was fully determined by sigma-electrons.
PB  - Wiley-V C H Verlag Gmbh, Weinheim
T2  - Chemistry. An Asian Journal
T1  - Can Variations of (HNMR)-H-1 Chemical Shifts in Benzene Substituted with an Electron-Accepting (NO2)/Donating (NH2) Group be Explained in Terms of Resonance Effects of Substituents?
VL  - 13
IS  - 7
SP  - 877
EP  - 881
DO  - 10.1002/asia.201800137
UR  - Kon_3458
ER  - 
@article{
author = "Baranac-Stojanović, Marija",
year = "2018",
abstract = "The classical textbook explanation of variations of (HNMR)-H-1 chemical shifts in benzenes bearing an electron-donating (NH2) or an electron-withdrawing (NO2) group in terms of substituent resonance effects was examined by analyzing molecular orbital contributions to the total shielding. It was found that the -electronic system showed a more pronounced shielding effect on all ring hydrogen atoms, relative to benzene, irrespective of substituent +R/-R effects. For the latter, this was in contrast to the traditional explanations of downfield shift of nitrobenzene proton resonances, which were found to be determined by the sigma-electronic system and oxygen in-plane lone pairs. In aniline, the +R effect of NH2 group can be used to fully explain the upfield position of meta-H signals and partly the upfield position of para-H signals, the latter also being influenced by the sigma-system. The position of the lowest frequency signal of ortho-Hs was fully determined by sigma-electrons.",
publisher = "Wiley-V C H Verlag Gmbh, Weinheim",
journal = "Chemistry. An Asian Journal",
title = "Can Variations of (HNMR)-H-1 Chemical Shifts in Benzene Substituted with an Electron-Accepting (NO2)/Donating (NH2) Group be Explained in Terms of Resonance Effects of Substituents?",
volume = "13",
number = "7",
pages = "877-881",
doi = "10.1002/asia.201800137",
url = "Kon_3458"
}
Baranac-Stojanović, M.. (2018). Can Variations of (HNMR)-H-1 Chemical Shifts in Benzene Substituted with an Electron-Accepting (NO2)/Donating (NH2) Group be Explained in Terms of Resonance Effects of Substituents?. in Chemistry. An Asian Journal
Wiley-V C H Verlag Gmbh, Weinheim., 13(7), 877-881.
https://doi.org/10.1002/asia.201800137
Kon_3458
Baranac-Stojanović M. Can Variations of (HNMR)-H-1 Chemical Shifts in Benzene Substituted with an Electron-Accepting (NO2)/Donating (NH2) Group be Explained in Terms of Resonance Effects of Substituents?. in Chemistry. An Asian Journal. 2018;13(7):877-881.
doi:10.1002/asia.201800137
Kon_3458 .
Baranac-Stojanović, Marija, "Can Variations of (HNMR)-H-1 Chemical Shifts in Benzene Substituted with an Electron-Accepting (NO2)/Donating (NH2) Group be Explained in Terms of Resonance Effects of Substituents?" in Chemistry. An Asian Journal, 13, no. 7 (2018):877-881,
https://doi.org/10.1002/asia.201800137 .,
Kon_3458 .

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