A study is presented which shows how, in the Hems synthesis of two tri-ortho-substituted diphenyl ethers, the nature of the leaving group of the substrate is important in determining yield. The yield increases in the order: OTosyl (p-OSO2C6H4CH3) < Cl < F. As well, a synthetic method, involving reaction of an activated substrate with a sodium phenoxide in dimethyl sulfoxide, has been investigated in a similar way and a number of highly-hindered diphenyl ethers, which cannot be synthesized by the Hems synthesis, have been prepared.