Ground state effects

Influence of the Outer Coordination Sphere on Bond Lengths within the Complex 

Complexes in which apparently genuine internal effects are observed or which contain ligands such as SO and alkyl groups that are known to show marked thermodynamic and kinetic effects, are listed in Tables II and III (corrinoids). 

Compound X Cis group Bond length (A) Trans group Estimated standard Bond length deviation (A) (e.s.d.) Ref. 

Three alkyl complexes have been studied. The corrinoid, Co-5 -deoxyadenosylcobalamin, can be compared directly with cyanocobalamin, which differs only in the nature of one of the axial ligands. Since different bond lengths are apparently found in the wet and dry forms of 

Evidence from bond lengths can be summarized as follows  

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Ground-state effects, i.e., the effects on the bond lengths and angles, stretching and bending force constants, and other spectroscopic properties of the other ligands. 

The ground-state effective Hamiltonian is diagonal with eigenvalues ha n + 5], whereas the excited state one is that of a driven quantum harmonic oscillator that must lead to coherent states. 

Page demonstrated in 1992 in a critical analysis [73] that bicyclic /3-lac-tam antibiotics do not exhibit exceptional chemical reactivity. He concluded that neither kinetic nor ground-state effects indicate a significant degree of inhibition of amide resonance in penicillins and cephalosporins [72] [74], Indeed, in comparison to normal amides, the /3-lactam N-atom does not exhibit any enhanced ability to donate its electron pair to either protons or metal ions [75] [76],... 

In contrast to the very strong dependence of reactivity on the electron displacement properties of the trans ligand, there is small response to such variations in the cis ligand. There are no obvious ground state effects (cis influences) and it must be concluded that the effect, such as it is, relates to transition state stabilization. This is borne out by the fact that the effect is more marked the... 

From a systematic study of bichromophoric compounds 97-99, the importance of substituents and solvent polarity in intramolecular deactivation processes of photoexcited anthracenes by nonconjugatively tethered, and spatially separated, aromatic ketones in their electronic ground state is apparent. For 97a-d, in which the electron acceptor properties of the aromatic ketone moiety have been varied by appropriate p-substitution of the phenyl ring (R is methoxy, H, phenyl, and acetyl, respectively), the longest-wavelength absorption maximum band lies at 388 nm, i.e., any ground state effects of substitution are not detectable by UV spectroscopy. Also, the fluorescence spectra of 97a-d in cyclohexane are all related to the absorption spectra by mirror symmetry. However, the fluorescence quantum yields for 97a-d in cyclohexane dramatically are substituent dependent (see Table 19), ranging from 0.20 for the methoxy derivative to 0.00059 for the acetyl compound [33,109],... 

The small ground state effect of a -silicon in the synperiplanar geometry compared to an antiperiplanar geometry is presumably the result of much poorer overlap between the oc si orbital and the neighbouring af. () orbital in the synperiplanar geometry (49) compared to the antiperiplanar geometry (50). 

Ground state /-effects of silicon may be responsible for the elongated C(alkyl)-O(ester) bond in n.s-3-trimelhylsilylcyclohexyl p-nitrobenzoate 59 relative to the silicon-free derivative. It is suggested that the ground state /-effect could be due either to homohyperconjugation, 60, or to inductively enhanced C—C hyperconjugation where the trimethylsilyl substituent increases the importance of the resonance form 61 relative to the silicon-free derivative. 

The effect of a-silyl substitution on the stability of a carbenium ion was qualitatively unclear for a long time. Early solvolytic studies by the groups of liaborn36 and Cartledge37 suggest a destabilizing effect of a-silyl substitution compared with alkyl. The measurement and interpretation of the kinetic a-silicon effect in solvolysis reactions is, however, often complicated by the fact that steric and ground state effects may play an important role and that, in addition, the rates of ionization often involve a contribution from nucleophilic solvent assistance. 

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