Functional cyclotrisiloxanes [(RMeSiO)(R'2SiO)(ClMeSiO)] (R=OSiMe3, OSi (OSiMe3)3; R'=OSiMe3) and [(PhMeSiO)2-(XMeSiO)] (X = H, Cl), each as a mixture of two configurational isomers, have been prepared and shown to be useful as model compounds for studying the stereochemical course of substitution reactions at siloxane silicon atoms by Si-29 or H-1 NMR spectroscopy. As an example, the acetolysis of the chlorocyclotrisiloxanes was studied and found to proceed with retention of configuration.