1. J. A. Durden and D. L. Heywood, J. Heterocycl. Chem., 9, 1331 (1972).
2. M. G. Voronkov and É. P. Popova, Izv. Akad. Nauk LatvSSR, Ser. Khim., 595 (1970).
3. Maximally Permissible Concentrations of Harmful Substances in Air and Water [in Russian], Khimiya, Leningrad (1972).
4. M. S. Skorobogatova, Ya. A. Levin, and O. A. Raevskii, Khim. Geterotsikl. Soedin., No. 9, 1171 (1970).
5. Varian Associates NMR and EPR Spectroscopy, Catalog, Vols. 1 and 2, Oxford (1960).