The necessary and sufficient
condition that the latin square formed by the Cayley multiplication table of a group
has an orthogonal mate is that the group has a complete mapping. Here, we define
two generalizations of the concept of a complete mapping and show how
these generalizations are related to sequenceable groups and R-sequenceable
groups respectively and that together they permit a complete characterization
of left neofields. In the second part of the paper, we shall show that these
generalizations also yield new constructions of block designs of Mendelsohn
type.