Progress in the chemistry of organoheterosiloxanes is reviewed in the light of the latest preparative and spectroscopic results. Attention is focussed on the heterosiloxane structural unit Si-0-X, the bonding in whichdepending on the hetero-atomdiflers characferistically from that in the siloxane bridge Si-0-Si.[7] H. Schmidbaur, Habilitation Thesis, Universitat Marburg,
1964.[ S ] See, for example, E. '4.