Volume II/17d1 is the first part of the fourth subvolume of a supplement to the previous compilations II/1 and II/9a-d on magnetic properties of free radicals, published in 1965 and 1977 - 1980, which covered the literature up to 1975. Due to the continuing rapid development of the field and the inclusion of new subjects, the supplement covering the period 1975 - 1985 had to be split into subvolumes which appear in fast succession. Together with earlier volumes, II/17 offers an up-to-date and comprehensive survey and a collection of data on important chemical intermediates. The series started with subvolume II/17a, which treats inorganic radicals and radical ions as well as radicals in metal complexes. Subvolume II/17b deals with nonconjugated carbon radicals. Subvolume II/17c covers conjugated carbon-centered and nitrogen radicals. Subvolumes II/17e and II/17f, which appeared at the end of 1987, are concerned with radicals centered on heteroatoms with Z > 7 and selected anion radicals. Subvolumes II/17d1 (presented herewith) and II/17d2 (early in 1989) treat nitroxide radicals.