Charge-transfer complexes of tetracyanoethylene with cycloalkanes, alkenes, and alkynes and some of their aryl derivatives

Spectral characteristics ({lambda}{sub max}, {Delta}{nu}{sub 1/2}, {epsilon}) and association constants (K) of charge-transfer (CT) complexes of tetracyanoethylene (TCNE) with 89 hydrocarbon donors (D) including cycloalkanes, alkenes, alkynes, benzene, benzene-d{sub 6}, alkylbenzenes, styrenes, biphenyls, polyphenylalkenes and phenylalkynes in CH{sub 2}Cl{sub 2} are presented. New data and reevaluation of older published data indicate that many donor/TCNE systems contain significant concentrations of the D{sub 2}(TCNE) in addition to the predominant D(TCNE) species. The donor orbitals from which CT transitions originate are determined by the correlation of {lambda}{sub max} and {Delta}{nu}{sub 1/2} values of CT bands of the complexes with the ionization bands in the photoelectron spectra of the donor molecules. Positive relationships between both CT energies and thermodynamic stabilities of complexes with respect to the number and geometry of substituent alkyls are established for alkene-, alkyne-, and alkylbenzene-TCNE complexes. The K values of functionally similar complexes are related to the bulk and location of substituent alkyl groups which sterically affect the interaction of the donor molecule and TCNE. Stabilities and CT energies of complexes are correlated with intramolecular conjugative and inductive effects between functional groups, as well as geometric and structural factors that control the angular orientation of the groups to each other.