CHARGE-TRANSFER COMPLEXES OF TETRACYANOETHYLENE WITH ALKYL, ALKENYL, AND ARYL DERIVATIVES OF OXYGEN

Spectral characteristics (lambda(CT)Delta nu(1/2), epsilon) and association constants (K) of charge-transfer (CT) complexes of tetracyanoethylene with donors containing a C-O bond (in CH2Cl2 solution) are presented and evaluated. The donors include alcohols, phenols, alkyl, aryl and vinyl ethers, peroxides, furans, anisoles, and polymethoxyarenes. The donor orbitals from which CT transitions originate are determined by the correlation of lambda(CT) and Delta nu(1/2) values of CT bands of the complexes with the ionization bands of the photoelectron spectra of the donor molecules. Relationships between lambda(CT) and K values with respect to the number, geometry, and bulk of substituent groups are established for alkylphenols and -anisoles. Alcohols, alkyl ethers, and cyclic aryloxy compounds donate electrons from the highest occupied nonbonding, n(b(1)), orbital of the oxygen atom to the pi* orbital of TCNE to form weak CT complexes which exhibit a single absorbance band. The lambda(max) depends upon the identity of alkyl substituent, increasing in the order of the inductive effect for acyclic alkyls, (Me < Et < i-Pr < t-Bu) and in the order of ring size (3 < 4 < 5 < 6) for cyclic alkyls. Phenols and aryl ethers donate electrons from the two highest occupied, b(1) and a(2), orbitals to the pi* orbital of TCNE to form CT complexes exhibiting two optical bands. In these donors the oxygen atom bound to the aryl substituent conjugates with phenyl pi orbitals through the nonbonded electron pair when the C-O-C moiety is coplanar with the aryl ring. The rotation of phenolic OH groups is not hindered by the presence of o-alkyl substituents, whereas the rotation of comparable OMe groups is hindered.