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?
Apstrakt
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.
Ključne reči:
benzene / density functional calculations / NMR spectroscopy / proton chemical shifts / substituent effectsIzvor:
Chemistry. An Asian Journal, 2018, 13, 7, 877-881Izdavač:
- Wiley-V C H Verlag Gmbh, Weinheim
Finansiranje / projekti:
Napomena:
- This is peer-reviewed version of the following article: Baranac-Stojanović, M. Can Variations of 1H NMR Chemical Shifts in Benzene Substituted with an Electron-Accepting (NO2)/Donating (NH2) Group Be Explained in Terms of Resonance Effects of Substituents? Chemistry - An Asian Journal 2018, 13 (7), 877–881. https://doi.org/10.1002/asia.201800137
- 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
Kolekcije
Institucija/grupa
Hemijski fakultet / Faculty of ChemistryTY - JOUR AU - Baranac-Stojanović, Marija PY - 2018 UR - https://cherry.chem.bg.ac.rs/handle/123456789/3180 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 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" }
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
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 .
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 . .