Bond-order alterations

The insignificant alterations of the geometry, the charge distribution (see Fig. 13), the frontier orbitals, and the bond orders introduced as the educt is transferred into the activated complex point out that the latter is educt-like. However, as the activation entropies show, the reaction partners have already been arranged. For the first (AS = —161 AS° = —136 JK-1 mol-1) as well as for the second propagation... 

The resulting change in electronic character of the q3 versus q1 ligand is reflected in the altered symmetry, bond lengths, and NRT bond orders of allylic C—C bonds,... 

In contrast, resonance delocalization and bond alternation in the C—C=C—C backbone are only slightly affected by H-bond formation (namely, the C4—C5 bond order varies by only 0.008 between H-bonded and open conformers), because such resonance shifts do not intrinsically alter the charge distribution in the H-bonded O- H—O triad. This example illustrates the principle that H-bonding is not generally coupled to resonance per se, but only to such resonance as leads to effective CAHB enhancement (Section 5.2.2). 

Js.JJa.s in these systems is 0.5, indicating appreciable bond length alterations. 74.5 is very similar to 7o of benzene (9 Hz), while 75.6 is only 4.0 Hz. In the pyrazolo[l,5-fl]pyrazine ring system, H-6 and H-7 appeared at low fields (> 8.1 ppm), and Jej is only 5 Hz, indicating that bond order in these systems is less than in benzene (7o = 9 Hz) (74CPB1814). 

The off-diagonal entries rij = rji of the R-matrix R indicate the changes in formal bond order between the atoms Ai, Aj, and the diagonal entries rii of R denote alterations in the placement of lone valence electrons. 

To solve this equation for as2 we need to know the relationship of crx and ctbi, that is, whether the primary covalent bond order is altered upon coordination. For halocarbons as ligands there is generally no detectable lengthening of the bond noted by X-ray crystallography, which might justify the conclusion that ax [Pg.6235]

Results (Table I) from refinement of the powder neutron diffraction data for the Ce doped material, Bi 8 0 2 3 12 that significant structural alterations have resulcea from Ce incorporation into the solid The three Mo atoms are no longer chemically equivalent The coordination about Mo(l) is unchanged from that of the parent compound A second Mo atom contains two short (double) bonds to oxygen atoms These molybdate dioxo (dimolybdenyl) groups are believed to be an important feature for selective oxidation catalysis (7 ) The third Mo coordination sphere contains no Mo=0 bond Bond order calculations (27) about... 

It is worth noting that adding water as the solvent with the PCM continuum solvent model16 and the conductor field model of electrostatic interactions (COSMO)17 or even specific water molecules to the calculations did not alter the chlorine KIEs, nor the conclusion, significantly. Also noteworthy is the observation that neither the method of calculating the transition state bond order nor anharmonicity affected the conclusions. 

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