INDO calculations

Projected INDO the initial guess at the MO coefficients is obtained from an INDO calculation. 

A projected CNDO/INDO guess uses the computed coefficients from a minimum basis set CNDO/INDO calculation and then... 

While INDO calculations have more parameters and are somewhat more complex that CNDO calculations, they require essentially no extra computation time and in most situations they are superior to CNDO calculations. 

On the other hand, theoretical methods allow an insight into the structure of non-existent molecules like 2//-indazole (37) or the anion of indazole (38). INDO calculations have been performed by Palmer et al. on the anion of indazole (38) (75JCS(P1)1695). The optimized geometry obtained by them is shown in Figure 7. The N—N bond distance is longer in the... 

More sophisticated procedures involve taking the start MO coefficients from a semi-empirical calculation, such as Extended HUckel Theory (EHT) or Intermediate Neglect of Differential Overlap (INDO) (Sections 3.12 and 3.9). The EHT method has the advantage that it is readily parameterized for all elements, and it can provide start orbitals for systems involving elements from essentially the whole periodic table. An INDO calculation normally provides better start orbitals, but at a price. The INDO... 

INDO calculations were applied to five 4-substituted benzenediazonium ions by KovaFchuk et al. (1988). It is known, however, that this relatively old method is of limited accuracy for the determination of geometrical parameters for such compounds. 

Prasad and coworkers60 studied the ESR spectra of cation radicals of dienes, trienes, tetraenes and pentaenes formed in CFCI3 matrix by X-ray irradiation. The structures of the resulting cation radicals were deduced by comparing the experimental coupling constant to those derived from INDO calculation. The unpaired spin density decreases with increasing chain length. 

The early calculations on cycloheptatrienylidene (4a) uniformly found it to be higher in energy than allene 3a. INDO calculations by W.M. Jones and co-workers predicted carbene 4a to be 14 kcal/mol less stable than allene 3a.28a Waali s MNDO calculations predicted that singlet 4a is 23 kcal/mol less stable than 3a, and that 4a serves as a transition state for the enantiomerization of 3a.28c,e The HF/4-31G ab initio calculations of Radom et al. also found both singlet and triplet states of 4a to be less stable than allene 3a.29a... 

Results of INDO calculations of cis and trans 1,3-butadiene are shown below and are in complete agreement with the predictions of our theoretical model ... 

Good quality ab initio calculations have not yet been carried out in order to test whether lone pair nonbonded attraction obtains in 1,2-difluoroethane. Results of INDO calculations shown below indicate the presence of a nonbonded attractive interaction on the basis of the partial bond order p (F2px, F2px). By contrast, the presence of a nonbonded repulsive interaction favoring the anti conformation is indicated on the basis of the bond order p(F2px, F2px). 

However, INDO calculations have been performed for the cis and trans isomers of l,2-difluoro-l,2-dihydroxyethylene and the results are shown above. As can be seen, the total overlap population is the same in both cases and, hence, the difference in the stabilities of the cis and trans isomers is expected to be very small. 

Results of INDO calculations for staggered and eclipsed CH3COX are shown above and support our analysis. Specifically, a lower energy of the eclipsed conformation can be attributed to pi nonbonded interaction since the total pi overlap population is larger in the conformation relative to the S conformation. 

The results of INDO calculations of planar and distorted difluorobenzene in which the C—F bonds have been displaced a few degrees above and below the mean plane, are shown above. As can be seen, the planar geometry maintains pi nonbonded attractive interaction. Sigma lone pair interactions will be similar to those which obtain in 1,2-difluoroethane and appear to be repulsive in nature. 

Results of INDO calculations are shown below for cis and tram 2,3-difluoro-butadiene. 

INDO calculations of the Cs and Ce conformations of N-methyl formamide shown above clearly indicate that the greater stability of the Cs conformation is due to pi nonbonded attractive interactions. 

Further doubt about the validity of the original Grant-Cheney model was expressed by Seidman and Maciel (185), whose INDO calculations of proximity effects in hydrocarbons revealed that there is no simple correlation between carbon chemical shifts and calculated electron-density increases caused by steric C-H bond polarization they report the conformational relation of interacting bonds and groups to be at least equally important, if not more so (185). 

The observed ya-SCS(X) values in 7-exo-substituted norcaranes 97 (225) and those of M(CH3)3 (M = Si, Ge, Sn, or Pb) in cyclohexyl and bicy-clo[2.2. l]heptane derivatives (133) were later interpreted on the same basis. The back-lobe-overlap treatment was further supported by interpretations of H and 13C contact shifts of aliphatic amine signals in the presence of nickel acetyl-acetonate and by INDO calculations (226,227). Additional support came from extensive investigations of the structure dependence of three-bond coupling constants 3JCX (X = H, C, or F) (228,229), although the interpretation of these data has been subjected to criticism (230). 

Figure 5. Relationship between Jqu the C-O-C-H dihedral angle represented by equation (4) (full line). Squares represent FPT-INDO calculations, stars represent experimental values from Ref. 5.

The charge distributions of the sydnone ring calculated by these ab initio methods show one significant difference from those given by CNDO and INDO calculations, namely a reversal of the positive and negative charges on the nitrogen atoms. 

---