Ring strain in [n]ladderanes.

The ring strain energies in a series of [ n]ladderanes (n = 3-8) have been calculated by using high-level ab initio method (G3MP2//B3LYP-6-31G*) and the series of isodesmic, homodesmotic, and protobranching compensated reactions. The results show that various four-member rings incorporated into the ladderane chain have different strain energies and that the total strain in a ladderane molecule is smaller than the corresponding sum of strain energies of the cyclobutane rings.