Molecular diagram

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. 

Oxadiazole, 2-phenyl-melting point, 6, 430 molecular diagrams, 6, 428 reactions... 

The following molecular diagrams show the major constituents of LPG ... 

Figure 6.9 (a) Standard deformation density of tetrafluoroterephthalonitrile in the molecular plane. Contour interval is 0.1 e A-3, terminated at 1.5 e A 3. (b) Molecular diagram with a box around the fragment shown in the deformation map (a). (Reproduced with permission from F. L. Hirshfeld, Acta Crystallogr., B40, 613, 1984.)... 

The question of the identity of the reactive excited state was left open, although n-n excited state was considered to be more probable.140 The interaction diagram, Fig. 7, shows that a n-n state would have an additional stabilizing interaction Ri(tt) ->-R2(7r) with orbital coefficients in phase for an all-suprafacial concerted reaction. The dominant reaction would theoretically depend upon the relative placements of the several levels, and since no experimental information for maleic and fumarate esters is presently available, a clear choice cannot be made. It is interesting that the reactive excited state could be inferred if both stereochemistry and a good molecular diagram were available. 

Each molecular diagram shows the results of four calculations (5a, r = 3,5,6,8) and should not be confused with the charge distribution of a single calculation such as that shown in Fig. 2. The results show... 

The chemist s sketch, processed into the list representation just described, is not yet very valuable the system at the moment is very ignorant of the structure of the molecule in question. But the chemist knows much of the molecule from little more than the diagram. How does the chemist "see" a complex molecular diagram ... 

Figure 3.3 Molecular diagram of [(TIMEN )3lr(COD)3](PF6)3. The hydrogen atoms and counterions (PFs) have been omitted for clarity.

Structural and theoretical studies on these systems are scarce. A molecular diagram (bond orders, electron densities) of 2-phenyloxazole[3,2-/]xan-thine has been reported (HMO method with standard parameters... 

FIG. 10.11 Electron density in the metal-ligand plane of dichromium tetraacetate, (a) Molecular diagram, (b) deformation density through Cr—Cr and the acetyl group averaged over equivalent regions. Contours are at 0.10 eA-3. Negative contours are broken lines. Source Benard et al. (1980). 

Figure 6. Molecular diagram of N,lSr-Diphenylguanidinium dihydrogen phosphate, GOLTOQ.

Bond graphs are familiar in organic chemistry where they are called molecular diagrams. The network of an organic molecule contains a finite number of atoms and bonds, and, because bonded atoms are always neighbours in three-dimensional space, such a bond graph can easily be drawn as a two-dimensional projection of the three-dimensional molecular structure. 

Fig. 7.6. The bond graph of oxalic acid dihydrate (OXACDH04) showing the observed bond valences. This graph shows the correct connectivity, but is not a three-dimensional molecular diagram.

The reductions are a result of successive filling of low-lying tlu orbitals, while the oxidation is due to the removal of electrons from the hu orbitals, as shown in the partial molecular diagram in Fig. 8.2. 

The sum of all these factors for a specific problem is equal to the trace of the matrix of the corresponding characteristic problem4 the sum of their squares equals the sum of the squares of all matrix elements of the corresponding characteristic problem.64 These relations are useful for checking the values of orbital energies. By an equally simple procedure1-4 the values of expansion coefficients yield the values of ir-electron densities (q), bond orders (p), and free valences (F) these quantities are usually presented in the form of a molecular diagram ... 

The values of orbital energies and molecular diagrams are given in ref. 61. Quite interesting is the finding that electron-withdrawing substituents such as CF3 strongly stabilize the cyclic form 50. 

Cation 73, synthesized a short time ago,90 is the simplest known derivative of the 1,2-dithiolium ion. Figure 7 presents molecular diagrams of 75 and 77. 

Fio. 8. Molecular diagram of thiothiacoumarin (for parameters see footnote b in Table IX).1 ... 

Fig. 9. Molecular diagrams of trithione (A, according to Bergson107 B, HMO, Model A1, C) and benzotrithione (C).16...

FlO. 12. Molecular diagram of a sulfur-aza analogue of heptalene (Model Al, C).18... 

Further, a systematic study of energy characteristics in a series of azines containing 2-4 nitrogen atoms in the molecule and of dihydro-azines has been published.29,30 A correlation was found between the calculated quantities and the experimental electronic excitation energies as well as the stabilities. Molecular diagrams were calculated for a selected group of representatives. Quite recently, various HMO and SCF characteristics have been calculated for a series of pyridinelike heterocycles and their amino derivatives.31... 

A mathematical analysis of all four isomeric thiadiazoles by the simple molecular orbital method has provided molecular diagrams of the free base and conjugate acid of each thiadiazole, with electron densities, bond orders, and free valencies. On this basis, predictions have been made concerning the reactivities of the six non-equivalent carbon atoms, the basicities of the nitrogen atoms, and the delocalization energies in these molecules. The 5-position in free 1,2,4-thiadiazole should possess maximum reactivity in nucleophilic substitution reactions. The treatment also accounts for the order of the polarographic half-wave potentials and the position of the absorption maxima in the ultraviolet region of the spectra of 1,2,4- and 1,3,4-thiadiazoles.4... 

Disparity between the observed moment and that calculated by vector addition of the individual group moments may indicate that the actual structure is not truly represented by the simple molecular diagram. There are several instances of the application of this technique to structural investigations in the field of O- heterocyclic chemistry, not the least of which is the question of the aromaticity of pyranones and their benzologues. 

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