Wave functions, CNDO

The C-H spin couplings (Jen) have been dealt with in numerous studies, either by determinations on samples with natural abundance (122, 168, 224, 231, 257, 262, 263) or on samples specifically enriched in the 2-, 4-, or 5-positions (113) (Table 1-39). This last work confirmed some earlier measurements and permitted the determination for the first time of JcH 3nd coupling constants. The coupling, between a proton and the carbon atom to which it is bonded, can be calculated (264) with summation rule of Malinovsky (265,266), which does not distinguish between the 4- and 5-positions, and by use of CNDO/2 molecular wave functions the numerical values thus - obtained are much too low, but their order agrees with experiment. The same is true for Jch nd couplings. 

Table 1.10. Coefficients of Wave Functions Calculated for Methyl Cation by the CNDO/2...

An ab initio HF calculation with a minimum basis set is rarely able to give more than a qualitative picture of the MOs, it is of very limited value for predicting quantitative features. Introduction of the ZDO approximation decreases the quality of the (already poor) wave function, i.e. a direct employment of the above NDDO/INDO/CNDO schemes is not useful. To repair the deficiencies due to the approximations, parameters are introduced in place of some or all of the integrals. 

Giessner-Prettre, C., and A. Pullman. 1975. On the Molecular Electrostatic Potential Obtained from CNDO Wave Functions. Theor. Chim. Acta 37, 335. 

Fig. 20. Integrated electron density differences in the systems H2O-IJ+ and H2CO-Li+ calculated in the CNDO/2 approximation. (Wave functions taken from Ref. 224))...

Ellis, Squire, and Jaffe have carried out a detailed study of the spin-orbit coupling in formaldehyde and azulene. The wave functions were calculated using the CNDO/S method, which is more general than the PPP method discussed earlier and also allows ff-orbitals to be included. Let us review their findings on formaldehyde ... 

Several other molecular orbital models have been applied to the analysis of VCD spectra, primarily using CNDO wave functions. The nonlocalized molecular orbital model (NMO) is the MO analog of the charge flow models, based on atomic contributions to the dipole moment derivative (38). Currents are restricted to lie along bonds. An additional electronic term is introduced in the MO model that corresponds to s-p rehybridization effects during vibrational motion. 

CNDO/S wave functions, was correct536. This result allowed the correction of the assignments of the spectra of 1-acetylisatin538 539 540 and of 1-methyli satin and 3-... 

The quantitative effect of changes in AE on the cnmr shifts for several heterocycles was explored by Fraenkel (Tokuhiro and Fraenkel, 1969). They concluded that the experiment was critically dependent on the MO approach chosen to calculate the charge densities and A s and found that the Bene-Jaffe CNDO wave functions, gave the best correlation. The best calculated and observed chemical shifts are given in Table 11, and plotted in Figure 22. The scatter from the perfect correlation line is quite acceptable, but the approach... 

The CNDO/2 method (a particular type of parametrization of the CNDO method) has been and is being used widely by various investigators to determine approximate electronic wave functions and energies. 

Two-photon absorptivities calculated from CNDO/S Cl wave functions for substituted benzenes Power dependence of the MPI and fragmentation of bromobenzene. Mass-resolved studies in qualitative agreement with kinetic model... 

Evaluation of A jb by this method has been applied to the 2-pyridone and 4-pyridone tautomers systems using CNDO/2 wave functions. Three hydration sites were found for both 2-hydroxypyridine and 2-pyridone, yielding a net difference of 20 kJ mole-1 in favor of 2-pyridone. Three hydration sites were found for both 4-hydroxypyridine and 4-pyridone, resulting in A Ik = 17.2 kJ mole-1. The preferred hydration sites determined by this method are in complete agreement with those obtained by the supermolecule and OMTP methods (see Table VI). 

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