Sergio Santini

Molecular complexes of heteroaromatic five membered ring compounds with tetracyanoethylene. Charge transfer spectra, equilibrium constants and ionization potentials of the donors

Charge transfer complexes between heteroaromatic five membered ring compounds and tetracyanoethylene have been studied in solution at 20°C. Spectra, stability constants and empirical calculations of ionization energies confirm the π→π* nature of these complexes and that the inner orbitals of the donors are involved in the c.t. interaction.

Molecular complexes of substituted diphenyl sulphides with π acceptors. Charge transfer spectra and ionization potentials of the donors

Charge transfer complexes of substituted diphenyl sulphides as donors with tetracyanoethylene, 2,3-dichloro-5,6-dicyano-p-benzoquinone and chloranil have been studied spectrophotometrically. From the energies of the charge transfer transitions, the ionization potentials of the donors have been obtained. From the formation constants of the complexes and ionization potentials of the donors evidence has been obtained on the mixed nature of the donor orbital. The role of inner valence orbitals in the complex formation is also discussed.

EQUILIBRIA AND DIPOLE MOMENTS OF IODINE COMPLEXES WITH PYRIDINES AND QUINOLINES

Equilibrium constants and dipole moments of the charge transfer complexes of some pyridine and quinoline methylderivatives (donors) with iodine (acceptor) have been determined and some charge transfer parameters of the complexes have been calculated. A linear correlation has been found between log Ket and pKa for the donors which have no substituent in ori/io-position with respect to the nitrogen. Moreover, for all compounds, a better correlation has been obtained between log Kct and the difference between the energies of electron promotion in the free and perturbed halogen molecule. The calculated contributions of dative structure and the blue shifts of perturbed halogen band are discussed in terms of steric hindrance, repulsion energy and donor-acceptor distance.

Charge transfer complexes of iodine with mercaptans and related sulphur compounds

Charge transfer complexes of iodine (σ acceptor) with ethyl and phenyl mercaptan, and diphenyl sulphide and disulphide (n-donors) have been studied in cyclohexane at 25°C. Spectral data, stability constants, enthalpies and entropies of complexation are reported. As comparison with literature data for related compounds, the stability of the complexes is correlated with the donor structure and discussed in terms of electronic and steric factors. The effect of substituents on Kct of thiophenols has been investigated leading to an Hammett reaction constant of –1.11.

Dipole moments and molecular conformation of aryl diarylmethyl sulphides

The electric dipole moments of X1C6H4(X2C6H4)CHSC2H4Y (X1= X2= H, p-CI, or p-Me, Y =m- or p-CI or p-Me) have been measured in benzene solution. Form the value found for [graphic ommitted] (114°) it is suggested that there is some mixing between the 3s orbital and the two 3p orbitals of the sulphur atom involved in the C–S bonds. It has been shown that there is free internal rotation about the bond between sulphur and the sp3 carbon atoms.

Charge transfer complexes of aryl diphenylmethyl sulphides with iodine and with tetracyanoethylene

Charge transfer complexes of iodine (σ acceptor) and tetracyanoethylene (π acceptor) with aryl diphenylmethyl sulphides, X1C6H4(X2C6H4)CH·S·C6H4Y, have been studied in cyclohexane and carbon tetrachloride at 25°. The effect of substituents X and Y on the charge transfer constant, Kct, is notably different. Y Substituents modify this constant much more than do X substituents. The presence in the donor molecule of two electron-donating sites could produce the formation of multiple equilibria. If the sulphide is regarded as a combination of diphenylmethyl and thiyl radicals, spectral and equilibrium data show that iodine interacts exclusively with the thiyl protion. On the other hand, tetracyanoethylene interacts competitively with both halves of diphenylmethyl phenyl sulphide to give two isomeric, stable 1:1 charge transfer complexes. The absence of multiple equilibria involving the formation of 2:1 and 1:2 stable complexes is discussed.

Charge-transfer complexes of iodine with diphenyl sulphides

Charge transfer complexes of iodine (a σ acceptor) with mono- and di-substituted diphenyl sulphides have been studied in cyclohexane at 25°. Spectral data, stability constants, and thermal parameters are reported. The data fit the Hammett equation with ρ values of –0·64 and –0·43 for mono- and di-substitution, respectively. The stability–structure correlation is discussed in terms of electronic and steric factors and gives information on the conjugative contribution from the π system to the interaction of the sulphur lone pair with iodine.

Electronic interactions in aromatic compounds. Direct electronic interaction between aromatic rings in conjugated and non-conjugated cis-compounds

A study of charge transfer equilibria between a series of cis- and trans-4-styrylpyridines and cis- and trans-1-(4-X-phenyl)-2-(4-pyridyl)cyclopropanes with iodine has been carried out in CCl4. Acidity constants for these heteroaromatic compounds were determined. The results obtained for the two types of measurements show that through-space conjugation, due to overlap of the non-parallel π-orbitals of the two aromatic systems, operated in both cis-systems.