Density matrix theory has been used to develop a computer program for the solution of a four-nuclear spin system. A description of the theory used to develop this program is given in Chapter Three. This theory has been used to study a range of p-substituted nitrosobenzenes. The activation parameters have been determined and for N,N-dimethyl-p-nitrosoaniline, a comparison has been made with previous studies which have used more approximate methods. The solvent dependency of the barrier to rotation has been investigated in the N,N-dialkyl-p-nitrosoanilines and no significant solvent dependence found. In the early stages of this thesis, attempts were made to find a tetrahedral cobalt (II) complex involving ligand exchange, but no such complex suitable for a detailed NMR investigation was found. The investigation, though unsuccessful, has been briefly reported. These findings may aid further work in this area.