scholarly journals How Do Proton Chemical Shifts Reflect Aromaticity ? Graph Theory of the Secondary Magnetic Field Due to Ring Currents

1986 ◽  
Vol 59 (12) ◽  
pp. 3781-3789 ◽  
Author(s):  
Jun-ichi Aihara
Keyword(s):  
Magnetic Field ◽  
Graph Theory ◽  
Chemical Shifts ◽  
Ring Currents ◽  
Proton Chemical Shifts

The theory of chemical shifts in nuclear magnetic resonance II. Interpretation of proton shifts

1957 ◽  
Vol 239 (1219) ◽  
pp. 550-556 ◽  
Keyword(s):  
Magnetic Field ◽  
Central Atom ◽  
Chemical Shifts ◽  
Considerable Effect ◽  
Electronic Current ◽  
Electronegativity Effect ◽  
Small Change ◽  
Proton Chemical Shifts ◽  
The Magnetic Field ◽  
Hf Calculations

The interpretation of proton chemical shifts is discussed in terms of the magnetic field due to the types of electronic current discussed in part I. It is shown that local paramagnetic circulations on neighbouring atoms may have a considerable effect on the resonance frequency. The anomalous position of the acetylenic proton can be ascribed to this effect. For the series of molecules CH 4 , NH 3 , H 2 O, HF, calculations show that there is an effect of paramagnetic currents around the central atom which increases along the series and which operates in the opposite direction to the electronegativity effect. It is suggested that the comparatively small change in the proton frequency along this series is due to cancellation of these terms.

scholarly journals Ring currents modulate optoelectronic properties of aromatic chromophores at 25 T

2020 ◽  
Vol 117 (21) ◽  
pp. 11289-11298 ◽  
Author(s):  
Bryan Kudisch ◽  
Margherita Maiuri ◽  
Luca Moretti ◽  
Maria B. Oviedo ◽  
Leon Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Nmr Spectroscopy ◽  
Density Functional ◽  
Chemical Shifts ◽  
Photophysical Properties ◽  
Magnetic Field Effect ◽  
Density Functional Theory Calculations ◽  
Zeeman Splitting ◽  
Magnetic Field Effects ◽  
Ring Currents

The properties of organic molecules can be influenced by magnetic fields, and these magnetic field effects are diverse. They range from inducing nuclear Zeeman splitting for structural determination in NMR spectroscopy to polaron Zeeman splitting organic spintronics and organic magnetoresistance. A pervasive magnetic field effect on an aromatic molecule is the aromatic ring current, which can be thought of as an induction of a circular current of π-electrons upon the application of a magnetic field perpendicular to the π-system of the molecule. While in NMR spectroscopy the effects of ring currents on the chemical shifts of nearby protons are relatively well understood, and even predictable, the consequences of these modified electronic states on the spectroscopy of molecules has remained unknown. In this work, we find that photophysical properties of model phthalocyanine compounds and their aggregates display clear magnetic field dependences up to 25 T, with the aggregates showing more drastic magnetic field sensitivities depending on the intermolecular interactions with the amplification of ring currents in stacked aggregates. These observations are consistent with ring currents measured in NMR spectroscopy and simulated in time-dependent density functional theory calculations of magnetic field-dependent phthalocyanine monomer and dimer absorption spectra. We propose that ring currents in organic semiconductors, which commonly comprise aromatic moieties, may present new opportunities for the understanding and exploitation of combined optical, electronic, and magnetic properties.

NMR-spektroskopische Untersuchungen über zwischenmolekulare Wechselwirkungen bei Benzolderivaten und Pyrrol / NMR-Spectroscopic Investigation of the Intermolecular Reactions of Benzene Derivatives and Pyrrole

1969 ◽  
Vol 24 (11) ◽  
pp. 1365-1370 ◽  
Author(s):  
H.-H. Perkampus ◽  
U. Krüger ◽  
W. Krüger
Keyword(s):  
Dipole Moment ◽  
Temperature Dependence ◽  
Aromatic Compounds ◽  
Spectroscopic Investigation ◽  
Chemical Shifts ◽  
Benzene Derivatives ◽  
Intermolecular Reactions ◽  
Proton Chemical Shifts

The proton chemical shifts of aromatic compounds are strongly concentration dependent. Moreever, for molecules with a dipole moment a temperature dependence of the proton chemical shifts is observed. For hemellitone, p-methylanisole, o-chlortoluene, p-chlortoluene, pyrrole and N-methyl-pyrrole the enthalpies of a dipole-dipole association between -0,7 and -1,8 Kcal could be estimated by NMR measurements combined with the temperature dependence in the whole range of the molefraction (0 → 1).

scholarly journals Real-time prediction of 1H and 13C chemical shifts with DFT accuracy using a 3D graph neural network

2021 ◽  
Author(s):  
Yanfei Guan ◽  
S. V. Shree Sowndarya ◽  
Liliana C. Gallegos ◽  
Peter C. St. John ◽  
Robert S. Paton
Keyword(s):  
Neural Network ◽  
Real Time ◽  
Quantum Chemical ◽  
Organic Molecules ◽  
Chemical Shifts ◽  
13C Chemical Shifts ◽  
Time Prediction ◽  
Nmr Data ◽  
Proton Chemical Shifts

From quantum chemical and experimental NMR data, a 3D graph neural network, CASCADE, has been developed to predict carbon and proton chemical shifts. Stereoisomers and conformers of organic molecules can be correctly distinguished.

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