Chemical Shifts and Ring Currents in Condensed Ring Hydrocarbons

Jonathan, Neville; Gordon, Sidney L.; Dailey, B. P.

doi:10.1063/1.1732906

Cited by 260 publications

(71 citation statements)

References 15 publications

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“…The simple dipole model evidently slightly overestimates the ring current contribution in benzene (11). An improved value of 1.5 p.p.m., used for the present work, was obtained by measuring the difference between the resonance shift of benzene and the shift of the olefinic protons in 1,3-cyclohexadiene.…”

Section: For Benzene Itself This Gives a Contribution T O The Proton mentioning

confidence: 85%

Proton Magnetic Resonance Shifts and the Electron Density Distribution in Aromatic Systems

Schaefer¹,

Schneider²

1963

Can. J. Chem.

235

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The quantitative nature of the empirical linear correlation between the proton resonance shifts in aromatic molecules and the local electron density on the carbon atom to which the proton is bonded has been investigated. The application of this relationship t o the determination of the electron density distribution of a variety of aromatic molecules, as well as the main limitations inherent in this application, are discussed. Electron density distributions have been derived for aniline, anisole, azulene, acepleiadylene, pyridine, pyridinium ion, and for the aromatic ions pentalenyl, indenyl, fluorenyl, triphenylmethyl cation, and azulene dianion, and are compared with those calculated by molecular orbital methods. In general there is a fairly good correspondence between the experimental and calculated density values, although for the aromatic ions the excess charge tends t o be somewhat more uniformly distributed over the molecule than would be indicated by simple MO calculations.

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Section: For Benzene Itself This Gives a Contribution T O The Proton mentioning

confidence: 85%

Proton Magnetic Resonance Shifts and the Electron Density Distribution in Aromatic Systems

Schaefer¹,

Schneider²

1963

Can. J. Chem.

235

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“…This all results in calculated ring-current intensities (relative to benzene) of 1.459 (for the outer rings of coronene) and 1.038 (for the inner ring), in satisfactory agreement with the well-established literature values. 72,73,22,23 (…”

Section: Calculationsmentioning

confidence: 99%

An Analysis of Topological Ring-Currents and their Use in Assessing the Annulene-Within-an-Annulene Model for Super-Ring Conjugated Systems

2013

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Abstract. The Hückel-London-Pople-McWeeny approach to calculating ring currents in conjugated systems is considered in detail, especially the 'topological' variant of this formalism, particularly emphasised during the last five years. A step-by-step account is given of how these calculations are effected in practice, in such a way as to enable any interested reader to carry out these computations himself. The method is illustrated by using it to assess the applicability of the so-called 'Annulene-Within-an-Annulene (AWA) Rule' to 'super-ring' conjugated hydrocarbons -some in which the inner ring and outer perimeter are 'coupled', and others in which they are 'decoupled'. Compliance with the AWA model appears more probable in decoupled super-ring structures than in coupled ones. The Appendix touches on previous work involving Professor D. J. Klein, the honorand of this issue. (doi: 10.5562/cca2291)

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“…However three systematic investigations attempted to overcome these difficulties. Jonathan et al 12 analysed the proton spectra of several condensed aromatics at infinite dilution in CCl 4 or CS 2 . They then used the Pople-London theory to calculate the current intensity in the benzenoid rings and the Johnson-Bovey tables 5 to obtain the ring current shifts.…”

Section: Introductionmentioning

confidence: 99%

Proton chemical shifts in NMR. Part 14. Proton chemical shifts, ring currents and π electron effects in condensed aromatic hydrocarbons and substituted benzenes

Abraham

Canton

Reid

et al. 2000

J. Chem. Soc., Perkin Trans. 2

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The proton resonance spectra of a variety of condensed aromatic compounds including benzene, naphthalene, anthracene, phenanthrene, pyrene, acenaphthylene and triphenylene were obtained in dilute CDCl 3 solution. Comparison of the proton chemical shifts obtained with previous literature data for CCl 4 solution shows small but significant differences. A previous model (CHARGE6) for calculating the proton chemical shifts of aliphatic compounds was extended to aromatic compounds. This was achieved by including an automatic identification of both five-and six-membered aromatic rings based on atomic connectivities plus a dipole calculation of the aromatic ring current. The ring current intensity in the molecules was calculated by two alternative methods. a) The ring current intensity in the individual benzenoid rings was a function of the number of adjoining rings and b) the molecular ring current was proportional to the molecular area divided by the molecular perimeter. This, plus the inclusion of deshielding steric effects for the crowded protons in these molecules, gave a good account of the observed chemical shifts. The model was also applied successfully to the non-alternant hydrocarbons of fulvene and acenaphthylene and to the aliphatic protons near to and above the benzene ring in tricyclophane and [10]cyclophane.The Huckel calculation of the π electron densities in CHARGE6 was used to calculate the π electron densities in substituted benzenes. The π-inductive effect was used to simulate the effect of CX 3 groups (X = H, Me, F) on the benzene ring. These together with the long range effects of the substituent groups identified previously allowed a precise calculation of the SCS of a variety of substituents on all the benzene ring protons.The model gives the first accurate calculation of the proton chemical shifts of condensed aromatic compounds and of the proton SCS in the benzene ring. For the data set of 55 proton chemical shifts spanning 3 ppm the rms error of the observed vs. calculated shifts was ca. 0.1 ppm. The model also allows the interpretation of the shifts in terms of the separate interactions calculated in the programme, i.e. π electron densities and steric, anisotropic and electric field effects. Previous correlations of the proton SCS with π electron densities and substituent parameters are shown to be over simplified. The relative proportions of these different interactions are very different for each substituent and for each ring proton.

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Chemical Shifts and Ring Currents in Condensed Ring Hydrocarbons

Cited by 260 publications

References 15 publications

Proton Magnetic Resonance Shifts and the Electron Density Distribution in Aromatic Systems

Proton Magnetic Resonance Shifts and the Electron Density Distribution in Aromatic Systems

An Analysis of Topological Ring-Currents and their Use in Assessing the Annulene-Within-an-Annulene Model for Super-Ring Conjugated Systems

Proton chemical shifts in NMR. Part 14. Proton chemical shifts, ring currents and π electron effects in condensed aromatic hydrocarbons and substituted benzenes

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