[2+2] Cycloaddition Products of Tetradehydrodianthracene: Experimental and Theoretical Proof of Extraordinary Long C-C Single Bonds

摘要

C-C bonds in organic molecules can be elongated by a number of factors. Steric repulsion between bulky substituents, strain energy in polycyclic systems, and through-bond interactions are among the most important. An impressive example of extremely long C C bonds (1.710-1.724 A), which is the result of the interplay of several of these factors, was recently described by Toda, Tanaka. Stein, and Goldberg. Otherclassical examples within the class of pure hydrocarbons include anthracene dimers and related compounds, in which the central C-C bonds between the anthracene units usually exceed 1.6 A. We demonstrate here with two compounds examined by both experimental and theoretical methods how the length of a C -C bond in a pure hydrocarbon can be extended to more than 1.7 A.