Je. Frey et al., CHARGE-TRANSFER COMPLEXES OF TETRACYANOETHYLENE WITH ALKYL, ALKENYL, AND ARYL DERIVATIVES OF OXYGEN, Journal of organic chemistry, 59(7), 1994, pp. 1817-1830
Spectral characteristics (lambda(CT)Delta nu(1/2), epsilon) and associ
ation constants (K) of charge-transfer (CT) complexes of tetracyanoeth
ylene with donors containing a C-O bond (in CH2Cl2 solution) are prese
nted 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 spectr
a of the donor molecules. Relationships between lambda(CT) and K value
s with respect to the number, geometry, and bulk of substituent groups
are established for alkylphenols and -anisoles. Alcohols, alkyl ether
s, and cyclic aryloxy compounds donate electrons from the highest occu
pied nonbonding, n(b(1)), orbital of the oxygen atom to the pi orbita
l 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, (M
e < Et < i-Pr < t-Bu) and in the order of ring size (3 < 4 < 5 < 6) fo
r 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 o
rbitals through the nonbonded electron pair when the C-O-C moiety is c
oplanar 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.