“…We provided a systematic definition of the geminal interactions of different combinations of substituents, donors (OR, NR2, F) or acceptors (CN, CO2R, COR) and we investigated the interaction of two or three different or identical substituents on the central C-atom. As a result it was shown that electron donating substituents like alkoxy groups (in acetals [2,11] and ortoesters [7]) or amino groups (in aminales [8]) experience synergetic stabilization, generally called "anomeric stabilization," which is mainly caused by 7r-a* conjugation (a through bond effect). On the contrary, combinations of electron-withdrawing substituents (CN, COOR, COR) show a destabilizing synergetic effect [1,5,9,13] mainly caused by repulsive interaction through space.…”