An introduction to phosphoranes is presented. Phosphoranes were synthesized to obtain data on the relative thermodynamic apicophilicities of ligands and to compare these data with known data on the relative kinetic apicophilicities of ligands. The relative thermodynamic apicophilicity of phenoxy and p-fluorophenoxy was found to be larger than expected and the relative thermodynamic apicophilicity of oxygen and sulphur was found to be too large to be observed suggesting that relative thermodynamic apicophilicities of ligands are greater than the corresponding relative kinetic apicophilicities. A range of P-2-furylphosphoranes was synthesized to gain data on the relative kinetic apicophilicity of the 2-fury1 group. The apicophilicity of 2-fury1 varied with other P-substituents' over quite a large range. A series of P-phenylselenophosphoranes was synthesized and data on the relative kinetic apicophilicity of phenylseleno were obtained. It was found that phenylseleno has a similar apicophilicity to phenylthio and phenoxy. Phosphoranes containing prochiral centres were synthesized and from their variable temperature n.m.r. spectra it was concluded that prochiral centres could be used as probes in pseudorotations.