On the basis of ab initio calcns. by means of electron d. contour maps and BSP's of individual valence MO's, it is found that all the stable configurations of the three title compounds have a double bridge 4-center bond. The reason for that is such a configuration is in favor of the electron drawing effect of the Li 2p-orbitals, which may strengthen the C-Li bonds. Within these 3 compounds C-C is stronger than C=C, the latter is stronger than CYC. This seems to be somewhat abnormal. The reason of such an abnormality has been discussed.

Key words: ETHYLENE P, CHEMICAL BONDS, AB INITIO CALCULATION, MOLECULAR ORBITAL THEORY, ACETYLENE P, CONFIGURATION, ETHANE P, CHARGE DENSITY, ORGANO LITHIUM COMPOUNDS