... been described [LM Jackman, "Application of Nuclear Magnetic Resonance Spectroscopy in Organic Chemistry," Pergamon Press ... Y., 1959, p. 63; and more recently: H, Spiesecke and W. G . Schneider, J . Chem. ... 88, 1406 (1963); J. Martin and B. P. Dailey, ibid., 89, 1722 (1963)l ...