Molecular method: Pariser-Parr-Pople

Indazoles have been subjected to certain theoretical calculations. Kamiya (70BCJ3344) has used the semiempirical Pariser-Parr-Pople method with configuration interaction for calculation of the electronic spectrum, ionization energy, tt-electron distribution and total 7T-energy of indazole (36) and isoindazole (37). The tt-densities and bond orders are collected in Figure 5 the molecular diagrams for the lowest (77,77 ) singlet and (77,77 ) triplet states have also been calculated they show that the isomerization (36) -> (37) is easier in the excited state. 

Indigo is the most important vat dye, dating back to ancient times and produced on an industrial scale since 1880. To replace the indigo dyes, the indanthrone (21) class of dyes was developed. Indanthrone has superior characteristics as a vat dye and became a key material for further development of anthraquinoid vat dyes. There exist a variety of anthraquinone vat dyes differing in the chromophoric system. The color-structure relationship of vat dyes have been rationalized by the Pariser-Parr-Pople molecular orbital (PPP MO) method. Some examples of commercialized anthraquinoid vat dyes are shown in Scheme 6.14... 

When parameters of the Pariser-Parr-Pople configuration interaction molecular orbital (PPP-CI MO) method were modified so as to reproduce the Aol)s values for l,3-di(5-aryl-l,3,4-oxadiazol-2-yl)benzenes 16 and 17, the calculated HOMO and LUMO energy levels corresponded with the experimental ionization potential and electron affinity values. The relationships between the electrical properties and molecular structures for the dyes were investigated. The absorption maximum wavelengths for amorphous films were found to be nearly equal to those for solution samples <1997PCA2350>. 

A semi-empirical ir-electron theory that takes electron repulsion into account is the Pariser-Parr-Pople (PPP) method (R.G. Parr. Quantum Theory of Molecular Electronic Structure, Benjamin, N.Y., 1963). 

Even if some interesting applications of the GHF-method had been found in solid-state theory [23,24], the applications to molecular systems were comparativlely few [40]. One major application to molecular systems had been worked out by Fukutome [40], and it was a study of the properties of the polyacetylene by means of the Pariser-Parr-Pople (PPP) approximation. It seemed hence desirable to make a molecular study based on ab-inttU) calculations to verify that one would get similar results and to get some experience in handling general Hartree-Fock orbitals of a complex nature, and for this purpose we started with some simple applications to atoms and to the BH molecule. 

M. Hida, unpublished results. b HMO, Hiickel molecular orbital theory. PPP, Pariser-Parr-Pople method. 

Pariser-Parr-Pople Method(PPP Method). The calculations are followed of the ordinary LCAO SCF MO Cl method with Tt-electron appro xlmat ion where molecular wave functions, g, of electronic... 

Among the earliest examples of the application of molecular orbital calculations to lignin chemistry is, as might be expected, the formation and reactivity of phenoxy radicals [32]. This work described the use of Pariser-Parr-Pople molecular orbital calculations, comparing various methods to determine the rr-electron spin densities for a number of model compounds. The different techniques gave similar results, with the bulk of the unpaired spin density at the phenolic oxygen, followed by the ortho and para carbons. In a cinnamaldehyde model, the P-position also exhibited considerable unpaired spin density. 

The Pariser-Parr-Pople method, self-consistent molecular orbital calculations, and the Huckel approach have been applied to the theoretical calculation of transition energies and intensities in the ultraviolet spectra of pyrido[2,3-ft]pyrazine and other azanaphthalenes. Good agreement with experimental data was obtained. The infrared spectra of the parent heterocycle" and its 8-hydroxy derivative have been discussed the 0X0 form is preferred to the hydroxy form both in chloroform solution and in the solid state. As with other a-hydroxyazines, the oxo form is also favored in the 2-, 3-, and 6-hydroxy compounds. Ultraviolet spectra have been measured for the parent heterocycle and various substituted compounds. The spectrum of the parent is substantially similar to other azanaphthalenes. In ethanol the principal bands are at ca. 260,300, and 350 nm. Both the infrared and ultraviolet spectra of about 60 derivatives of the ring system have been assembled. ... 

The 1998 Nobel prize in chemistry was shared by Walter Kohn, one of the developers of density-functional theory, and John A. Pople, one of the developers of the Gaussian series of programs and widely used Gaussian basis sets, the Pariser-Parr-Pople method, the CNDO and INDO methods, and one of the first to apply the MP and CC methods to molecular calculations. The Nobel committee noted that computational quantum chemistry is revolutionising the whole of chemistry. ... 

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