Abstract: In this paper, using semiempirical molecular orbitals MNDO procedures, the central bonds in small propellanes, such as [1. 1. 1], [2. 1, 1], [2. 2.1], [2. 2. 2] propellanes, are studied. The calculation results show that the strength of the side bonds in small propellanes is close to that of the bonds in common ring molecules, while the weaker covalent bonds are formed between the bridgehead carbon atoms than the bonds in common ring molecules. As the size of the rings in propellanes increases, the strength of the C-Ccentral bonds increases. Our theoretical calculations are in good agreement with the experimental and theoretical conclusions reported.

Key words: Propellanes, C-C central bonds, MNDO calculation