Bejoy K. Seal

Charge-transfer complex formation between o-chloranil and a series of polynuclear aromatic hydrocarbons.

The equilibrium constants, enthalpies and entropies of formation of molecular electron donor-acceptor (EDA) complexes of o-chloranil with a series of aromatic hydrocarbons have been determined spectrophotometrically. Spectroscopic and thermodynamic aspects of these complexes have been analysed.

Ground state EDA complex formation between [60]fullerene and a series of polynuclear aromatic hydrocarbons

Formation constants of 1∶1 adducts of [60]fullerene with naphthalene, phenanthrene, anthracene, pyrene and chrysene have been determined in CCl4 medium. Ionisation potentials of donor molecules and charge transfer (CT) transition energies of the [60]fullerene adducts have been found to correlate in accordance with the Mulliken equation. From such correlation the electron affinity of [60]fullerene has been calculated to be 2.32 eV in solution. A good estimate for the sp2C–sp2C resonance integral β in benzenoid hydrocarbons has also been obtained from the observed CT transition energies.

Studies on labile chargetransfer complexes between o-chloranil and a series of phenols

Abstract The electron donor–acceptor (EDA) interactions between o -chloranil and a series of phenols have been studied in dioxan medium. Except for resorcinol, the EDA complexes are formed instantaneously on mixing the donor and the acceptor solutions and then they decay slowly into secondary products. In case of resorcinol, formation and decay of the EDA complex are slow and simultaneous. The kinetics of all these reactions have been studied spectrophotometrically and the formation constants of EDA complexes have been determined from kinetic data. The hν CT values change systematically as the number and position of the –OH groups change in the aromatic ring of the phenol moiety. From the trends in the hν CT values, the Huckel parameters ( h O and k C–O ) for the –OH group, required for a PMO calculation on phenols, have been obtained in a straightforward way and the values so obtained, viz., 1.8 and 1.0 respectively, are close to the ones (1.8 and 0.8) recommended by Streitwieser on the basis of other evidences.

Independent determination of association constant and shift of the pure complex from NMR chemical shift data by a graphical method

which is the NMR analog of the well-known Benesi and Hildebrand (2) equation used for the determination of association constants and molar absorptivities of CT complexes from optical spectrophotometric data. The observed chemical shift is A, c”o represents the initial concentration of the donor which is taken in large excess over the concentration of the acceptor that is generally kept fixed throughout the experiment. Equation [l] has the disadvantage that in the linear plot of A-’ vs CK’ , A0 is evaluated from a relatively small intercept and may be subject to error which is reflected in Kc (particularly for weak complexes) evaluated from the product &A0 determined from the slope of the linear plot. As an alternative to Eq. [I] Foster and Fyfe (3) used the equation

Independent determination of equilibrium constant and molar extinction coefficient of molecular complexes from spectrophotometric data by a graphical method

Abstract The Benesi—Hildebrand equation and its modified forms have been rearranged to give equations which enable independent evaluation of K and ϵ of molecular complexes from spectrophotometric data by graphical procedure. The equations have been tested with data on several 1:1 complexes. The results agree fairly well with those determined by other well-known procedures.

Study of a novel reaction between N,N′-diphenylthiourea and p-chloranil through a charge-transfer intermediate

The well-known electron acceptor, p-chloranil (A) and donor, N,N′-diphenylthiourea (B) have been observed to form a labile charge-transfer (CT) complex (AB), which decays slowly into two products viz. 2,3,5-trichloro-6-(N,N′-diphenylthioureido)benzo-1,4-quinone (P) and 5,6-dichloro-2,3-(N,N′-diphenylthioureylene)benzo-1,4-quinone (Q). The final products have been isolated in pure form and one of them, P, has been shown to exhibit sensitive solvatochromism. A detailed kinetic study of the decay process of the CT complex has been carried out and based on kinetic data, the following steps have been suggested for the decay process.

Determination of the gas-phase value of the inductive effect parameter of the methyl group from solvatochromic study of the charge-transfer band maxima of complexes of tetracyanoethylene with methylbenzenes

From solvatochromicity of CT-band maxima of complexes of TCNE with methylbenzenes in several apolar and polar solvents the inductive effect parameter,hMe, of the methyl group has been calculated by the Coulson-Longuet-Higgins perturbation theory. From the measured solvent dependence ofhMc, the gas-phase value of the same has been determined to be −0·38 which is comparable with Streitwiesers recommended value ofhMe=−0·50. The higher value ofhMe in the gas phase than in solution has been explained.

ViscosityB-coefficients of sodium salts of some orthosubstituted benzoic acids in relation to hydrogen bonding and electronegativity

ViscosityB-coefficients of sodium salts of salicylic, thiosalicylic, anthranilic, 2,6-dihydroxy benzoic and ito-anisic acids have been measured at 298, 303 and 308 K respectively. Temperature dependence ofB-values suggest that the salts as well as their anions excepto-anisate behave as structure breakers. This is further supported by energy of activation data. The observedB-coefficients suggest probable involvement of simultaneous intra- and intermolecular hydrogen bonding between an ortho-substituent and the carboxylate group on the one hand and between the ortho-substituent and solvent water on the other. A good correlation betweenB-coefficients and the electronegativities of oxygen, nitrogen and sulphur atoms has been noted. The probable involvement of ringπ-electrons in depolymerising the water structure has been conjectured.