Ring currents, local anisotropy, and the problem of the out-of-plane protons: a reinvestigation of the nuclear magnetic resonance spectrum of [10]-paracyclophane

The 1 H nmr spectrum of [10]-paracyclophane has been recorded at 220 MHz and the methylene protons assigned on the basis of homonuclear decoupled spectra. Local anisotropic contributions to chemical shifts for protons sited above or near the aromatic ring of [10]-paracyclophane have been calculated using a classical model previously proposed by Grant. The residual incremental shift was shown to follow the Waugh–Fessenden–Johnson–Bovey classical ring current model, but the loop separation originally invoked was shown to be unnecessary. These corrected ring current contributions also correlate very well with the quantum-mechanical approach of Haigh and Mallion.