CNDO-MO calculations

Figure 31 CNDO/MO-calculated 29Si nuclear shielding for the central Si in Si11H24 as a function of dihedral angle.287 Reprinted with permission from Takayama, T. J. Mol. Struct. 1998, 441, 101-117, 1998 Elsevier.

As shown for the transformations of the cyclopentenyl methyl ketones (3a-d) to mixtures of (4a-d) and (5a-d) (Scheme 1), the ODPM rearrangement occurs from the lowest electronically excited p,y-enone triplet state. - The ir. ir configuration has been assigned to this state on the basis of CNDO-MO calculations, phosphorescence studies at 77 and mechanistic examinations. The phosphorescence data together with sensitization experiments have revealed a Ti energy range of 289-310 kJ mol (4.18 kJ = 1.0 kcal) for (3a-c) and a much lower Ti of 253 kJ mol for (3d). ... 

CNDO-MO calculations suggest that the Wittig olefin synthesis proceeds via 1,2-oxaphosphetans, which undergo P—C bond cleavage considerably in advance of P—O bond cleavage. 

The X-ray crystal structure of [Rh( n -CsH4Ph)( n -C2H4)2] has been reported and the conformation discussed in terms of CNDO-MO calculations. A series of rhodium-alkene complexes ctnitaining the potentially bidentate phosphine ligands [Pr P(CH2)nX] (n >2,3, X > NMe2 n>2, X > OMe) have been synthesised and characterised. Reaction of [RhCl(ri -... 

Effects of non-leaving ligands, and of chelating ligands in particular, on reactivities have been reviewed. The cis and trans influences, i.e. initial-state effects as far as kinetic phenomena are concerned, of some groups in platinum(ii) complexes have been assessed by CNDO-MO calculations. The cis influences were found to be comparable in magnitude to trans influences, but the ligand orders in the two series of influences were not identieal. ... 

A number of MO calculations has been carried out, and these have had mixed success in predicting chemical reactivity or spectroscopic parameters such as NMR chemical shifts and coupling constants. Most early calculations did not take into account the contribution of the sulfur 3d-orbitals to the ground state, and this accounts for some of the discrepancies between calculations and experimental observations. Of the MO methods used, CNDO/2 and CNDO/S have been most successful the INDO approximation cannot be used because of the presence of the sulfur atom. 

There have been ab initio studies of the bonding for a series of imino and amino phosphorus molecules,15 and for the phosphonium ylides (8).14 The anion character of the ylidic carbon is intermediate between that of olefinic and substituted carbanions. Polarisation of the H3P group has a stabilising effect. The influence of the substituent X on the inversion of the carbanion and also the tendency of the molecule to dissociate to carbene and phosphine is also discussed.14 CNDO/S MO calculations on the... 

Tapia, O., Poulain, E. and Sussman, F. Hydrogen Bond. Environmental effects on proton potential curves. An SCRF MO CNDO/2 calculation of a water dimer, Chem.Phys.Lett, 33 (1975), 65-70... 

Calculated and Observed Carbon-13 Chemical Shifts in Azines, Jaffe and Bene CNDO-MO s, Average Excitation Energy (AEE) and Different Excitation Energy... 

In order to consider the inversion of Qx(0,0) and Qy(0,0) electronic transition intensities in NH-tautomers of non-symmetrical free-base porphyrins we calculated the ground-state orbital energies of the investigated molecules by a CNDO/2 method using the symmetrized crystal geometry of porphyrin molecule (37,38). On the basis of the above experimental results we must introduce a motionless system of molecular X and Y axes, identically fixed in both tautomers. Then using theoretical MO calculations and the analysis... 

It is of interest to note (76JA171) that various MO calculations, SCF, MINDO/2 and CNDO/2, give widely different predictions with regard to pyridinone tautomerism in the gas phase, none of which is correct. This is particularly worrying, because they relate to... 

The results of Hiickel molecular orbital (HMO) calculations of the 7t-electron distribution in 287 indicate that N-1 is the most electron-rich center. Hiickel MO calculations for protonated species 288 and 289 indicate that 288 is more stable (7t-electron binding energies are 13.353 and 13.297 B). The all-valence electron CNDO/2 calculation for 287 yields virtually identical total electron densities (75CJC119). 

On the basis of CNDO/2 calculations on the model compounds 2.4.6-trimethyl-pyridine and 2.4.6-tri-methyl-X -phosphorin, Schweig and coworkers found that the MO sequences of pyridine and X -phosphorin do not correspond to each other. For simplicity, methyl- rather than tert-butyl groups were used in the calculations (whereas the PE and UV spectra of the tert-butyl compounds have been recorded the synthesis of the unsubstituted X -phosphorin was unknown at the... 

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