Tetrahydrofuran analogues with silicon and sulphur atoms

Quantum-mechanical calculations at the self-consistent-field-Moller-Plesset level have been performed for various compounds obtained by substituting two or four CH2 groups of the tetrahydrofuran molecule with SiH2 groups, as well as the oxygen with a sulphur atom. Cyclic tetrasilane oxide, (SiH2)(4)O, and sulphide, (SiH2)(3)S, are suggested as possible alternatives to the carbon ring of natural sugars for the design of exobiological molecules because of certain similarities with tetrahydrofuran, (CH2)(4)O, especially the relatively small energy differences between different conformers and the subsequent ability to cross the energy barriers between them by puckering on the pseudorotation wheel.