Ms. Masoud et al., Computerized electronic spectral properties of some azobarbiturate compounds in presence of different solvents, Z PHYS CHEM, 209, 1999, pp. 223-238
Citations number
36
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS
The solvent effects on the spectra of 5-(p-substituted phenylazo) barbituri
c acid have been analyzed by the multiple linear regression technique using
a Fortran TV program on a PC computer. The correlations based on one param
eter equation gave that the solute permanent dipole-solvent induced dipole
interaction (parameter M) plays the important role in determining the spect
ral shifts. The data based on two parameter equation gave that the solvent-
solute hydrogen bonding combined with the solvent permanent dipole-solute p
ermanent dipole interactions (E,N) are the important factors to explain the
spectral shifts. For the three parameter correlations, the compounds with
nitro, sulphonic, acetyl and iodo substituents gave that the combination (E
,M,K) gives a good fit to the observed spectral shifts. The HMO theory and
the PPP method explain the phenomena of tautomerism of barbituric acid. The
data predict that the diketo tautomer is the most stable one. Using the ca
lculated PPP binding energy and singlets transition for the dienol tautomer
which are nearly the same as those of the diketo tautomer to assign that a
mixture of the diketo and dienol tautomers coexist. The agreement between
the calculated and the experimental values of transition energies is reason
ably good. The phenomena of tautomerism of barbituric acid is studied based
on the Complete Neglect of Differential Overlap (CNDO) method.
Calculations have shown that the dioxo form is the most stable tautomer. Th
e singlets electronic transitions for 5-(p-substituted phenylazo) barbituri
c acid have been calculated by the CNDO method. The oscillator strength val
ues of 5-(p-substituted phenylazo) barbituric acid are calculated and found
to be affected by other factors e.g., the dielectric constant of the solve
nt, the electronic property of the substituent and the solvation energy.