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5. For general discussions see (a) G.C. Levy and G.L. Nelson. 13C Nuclear Magnetic Resonance for Organic Chemists. Wiley-Interscience. New York, 1972; (b) J.B. Stothers. Carbon-13 NMR Spectroscopy. Academic Press. New York, 1972; (c) N.K. Wilson and J.B. Stothers in Topics in Stereochemistry. Vol. 8. edited by E.L. Eliel and N.L. Allinger. Wiley-Interscience, New York. 1973. Chap. 1.