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Issue 16, 2018
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The halogen effect on the 13C NMR chemical shift in substituted benzenes

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Abstract

Recent research [Chem. Sci., 2017, 8, 6570–6576] showed for R-substituted benzenes with R = NH2, NO2 that the substitution effects on the 13C NMR chemical shifts are correlated with changes in the σ-bonding framework and do not follow directly the electron-donating or -withdrawing effects on the π orbitals. In the present work we extend the study to halogen (X = F, Cl, Br or I) substituted R-benzenes. The effect of X and R groups on 13C NMR chemical shifts in X–R-benzenes are investigated by density functional calculations and localized molecular orbital analyses. Deshielding effects caused by the X atom on the directly bonded carbon nucleus are observed for F and Cl derivatives due to a paramagnetic coupling between occupied π orbitals and unoccupied Image ID:c8cp01249k-t1.gif antibonding orbitals. The SO coupling plays an important role in the carbon magnetic shielding of Br and I derivatives, as is well known, and the nature of X also modulates the 13C paramagnetic shielding contributions. Overall, the X and R substituent effects are approximately additive.

Graphical abstract: The halogen effect on the 13C NMR chemical shift in substituted benzenes

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Publication details

The article was received on 24 Feb 2018, accepted on 28 Mar 2018 and first published on 29 Mar 2018


Article type: Paper
DOI: 10.1039/C8CP01249K
Citation: Phys. Chem. Chem. Phys., 2018,20, 11247-11259
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    The halogen effect on the 13C NMR chemical shift in substituted benzenes

    R. V. Viesser, L. C. Ducati, C. F. Tormena and J. Autschbach, Phys. Chem. Chem. Phys., 2018, 20, 11247
    DOI: 10.1039/C8CP01249K

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