organic compounds
In all three title compounds, C7H12O4, (1), C9H12O4, (2), and C7H12O2S2, (3), the spiro C-O distances are substantially shorter than the non-spiro C-O distances as a result of the anomeric effect. In contrast, the spiro C-S distances of compound (3) are similar to the non-spiro C-S distances. In all three compounds, steric repulsions between the lone pairs on the O or S atoms and the axial H atoms of the opposite ring result in a distorted geometry around the spiro-C atoms.