MACRO RINGS .40. TRANSANNULAR INTERACTIONS IN TETRACYANOETHYLENE COMPLEXES OF [3.3]PARACYCLOPHANE AND DERIVATIVES

Equilibrium constants for 1:1 7π-salt formation between tetracyanoethylene and [3.3]-, [3.4]-, [2.2]-, [1.9]-, [9]-, [4.4]-, and [6.6]paracyclophane were found to decrease in value in the order listed, the values being higher than that for the open-chain model compound, 1,3-bis(4-ethylphenyl)propane. A rough linear correlation between the equilibrium constants and the position of the λmax of the long-wavelength charge-transfer band in the visible spectrum of the π-salts has been observed for these and four monosubstituted [2.2]paracyclophanes. An exception to the correlation was the π-salt of [4.4]paracyclophane. The positions ofλmax values of the long-wavelength charge-transfer band of the π-salts of 13 substituted [3.3]paracyclophanes were determined. Possible correlations between ∆Et's (differences in electronic transition energies between the 5-substituted [3.3]paracyclophanes and [3.3]para-cyclophane itself) and substituent constants were examined. A rough linear correlation was observed between ∆Et values and óm constants for the electron-withdrawing substituents. The nonsubstituted ring was the more basic of the two, and was probably the main site of salt formation. This correlation demonstrates the presence of transannular electronic effects in the [3.3]paracyclophane system. Comparison of the slope of the plot for the [3.3]-paracyclophane derivatives with the formerly determined slope of the plot for the [2.2]paracyclophane derivatives demonstrated the transannular effects in the latter system to be greater. An even poorer linear correlation was observed between ∆Et of π-salts of [3.3]paracyclophane substituted with electron-providing groups and óA+ (π = 0.25) values. From its ∆Et value the acetamido substituent appeared to function as a moderately strong electron-withdrawing group when attached to [3.3]paracyclophane, whereas its óm value indicates that the group should be a weak electron donor. This abnormal behavior was also observed for 5-acetamido[3.4]paracyclophane, but not for 4-acetamido[2.2]paracyclophane. The 1:1 tetracyanoethylene-[3.3]paracyclophane salt was prepared in a crystalline form and analyzed. © 1969, American Chemical Society. All rights reserved.