1971
DOI: 10.1080/00268977100101061
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The calculation of chemical shifts in conjugated molecules

Abstract: Calculations are presented of the non-local pi-electron (ring current) contribution to the magnetic anisotropy of benzene and to the chemical shift experienced by an attached proton. The usual London Approximation (to simplify the integral evaluation) is not made, and the method thereby permits of a more detailed analysis of this approximation than has hitherto been possible.

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Cited by 10 publications
(2 citation statements)
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“…For a peripheral proton in a conjugated molecule subjected to an external magnetic field B 0 , at right angles to its molecular plane, ,− Here, B core derives from the inner-shell and σ-electrons and can be thought to include a ‘local' contribution from the π-electrons (thoughas one of us and Haigh have pointed out previously 2 this cannot be rigorously defined, even classically) and B ‘ is the contribution 2,147-150 from the induced π-electron ring currents. The latter is according to the familiar models put forward by Pople, very much in the spirit of the Pauling 131 /Lonsdale 132 approaches and much extended by others, both classically ,− , andthough still semiempiricallyquantum mechanically. When B ‘ is positive, as for a benzene proton, then at constant frequency (and, hence, constant B local ), a lower value of B 0 would be required for resonance. This term thus makes the benzene proton resonate at comparatively low field; the opposite is true for the cyclophane protons above a benzenoid ring, which therefore absorb at high field. , In, at least, semiempirical work, it is customary to subtract the resonance position of a given proton in a conjugated molecule from that of a hypothetical olefinic proton (similar, perhaps, to the olefinic proton in cyclohexa-1,3-diene 154 ) in the optimistic hope that both B 0 and B core in eq 14 may be eliminated, as localized effects would be expected to be very similar in the two cases.…”
Section: Nuclear Magnetic Resonance Chemical Shiftsmentioning
confidence: 93%
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“…For a peripheral proton in a conjugated molecule subjected to an external magnetic field B 0 , at right angles to its molecular plane, ,− Here, B core derives from the inner-shell and σ-electrons and can be thought to include a ‘local' contribution from the π-electrons (thoughas one of us and Haigh have pointed out previously 2 this cannot be rigorously defined, even classically) and B ‘ is the contribution 2,147-150 from the induced π-electron ring currents. The latter is according to the familiar models put forward by Pople, very much in the spirit of the Pauling 131 /Lonsdale 132 approaches and much extended by others, both classically ,− , andthough still semiempiricallyquantum mechanically. When B ‘ is positive, as for a benzene proton, then at constant frequency (and, hence, constant B local ), a lower value of B 0 would be required for resonance. This term thus makes the benzene proton resonate at comparatively low field; the opposite is true for the cyclophane protons above a benzenoid ring, which therefore absorb at high field. , In, at least, semiempirical work, it is customary to subtract the resonance position of a given proton in a conjugated molecule from that of a hypothetical olefinic proton (similar, perhaps, to the olefinic proton in cyclohexa-1,3-diene 154 ) in the optimistic hope that both B 0 and B core in eq 14 may be eliminated, as localized effects would be expected to be very similar in the two cases.…”
Section: Nuclear Magnetic Resonance Chemical Shiftsmentioning
confidence: 93%
“…The latter is according to the familiar models put forward by Pople, [151][152][153] very much in the spirit of the Pauling 131 /Lonsdale 132 approaches and much extended by others, both classically 139,[147][148][149][150][154][155][156][157][158][159][160] andsthough still semiempiricallys quantum mechanically. [161][162][163][164][165][166][167][168][169][170][171][172][173][174][175][176] When B′ is positive, as for a benzene proton, then at constant frequency (and, hence, constant B local ), a lower value of B 0 would be required for resonance. This term thus makes the benzene proton resonate at comparatively low field; the opposite is true for the cyclophane protons above a benzenoid ring, which therefore absorb at high field.…”
Section: A Definitionsmentioning
confidence: 99%