Reactant complex

The optimized structure of cispiatin in this study, the reactant complex, has a Pt-Cl bond distance of 2.44 A compared with... 

The optimized structures of the first water substitution are shown in Fig. 4.5. The initial reactant complex (RC1) is symmetric with the two water molecules located on the same side of the plane formed by the nonaquated cisplatin, the syn arrangement. The oxygen atoms of each water molecule are hydrogen bonded to one of the amine groups, at a distance of 1.7 A. The lowest vibrational level (31.9 cm 1) corresponds to the reaction coordinate for water substitution. An alternative complex with... 

Fig. 4.7 Reaction energy surfaces for the first and second aquation reactions of cisplatin starting from (a) the syn arrangement of the initial reactant complex and (b) the...

For the second substitution reaction, we have chosen to start from the guanine complex of conformer 1 only. The optimized geometric structures for the reactant complexes, transition states,... 

It should be noted that application of the Marcus theory to these reactions is much more straightforward than application to reactions in solution. Since we are dealing with a single unimolecular step, namely, rearrangement of the reactant complex to the product complex, we need not be concerned with the work terms (2) which must be included in treatments of solution-phase reactions. These terms represent the work required to bring reactants or products to their mean separations in the activated complex, and include Coulombic and desolvation effects. 

A prominent advantage of this assay procedure is the feature that the complex of hapten and labeled antibody was captured on a solid phase (PMP) and separated from the reaction medium before signal determination. This additional step not only reduces interference due to biological specimens but also eliminates the tedious transfer of supernatant, which is essential in conventional immunometric assays. This immunometric assay provided somewhat improved specificity in terms of the cross-reactivities with T2 and reverse T3 (3,3, 5 -L-triiodothyronine). The authors speculated that the dissociation rate of the antibody-cross-reactant complex would be faster than that of an antibody-analyte complex thus the former binding would be preferentially substimted by T2 immobilized on CPG. 

Figure 2 Characteristics of the HCl CIONO2 (H20)9 -action path. Energy referred to reactant complex.

For the unusual reactivity of ferrocenylsilanes toward 5u in THF, affording ketones instead of the expected tertiary alcohols, a mechanism was proposed including the inner-sphere electron transfer from 5u within a reactant complex. The proposition was based on an electrochemical CV examination, which indicated that the outer-sphere process is thermodynamically unfavorable. 

Scheme 7 Numbers are calculated enthalpy inkcalmol 1 at UHF/6-31G (G3) relative to reactant complex.

Sn2 reactions of methyl halides with anionic nucleophiles are one of the reactions most frequently studied with computational methods, since they are typical group-transfer reactions whose reaction profiles are simple. Back in 1986, Basilevski and Ryaboy have carried out quantum dynamical calculations for Sn2 reactions of X + CH3Y (X = H, F, OH) with the collinear collision approximation, in which only a pair of vibrations of the three-center system X-CH3-Y were considered as dynamical degrees of freedom and the CH3 fragment was treated as a structureless particle [Equation (11)].30 They observed low efficiency of the gas-phase reactions. The results indicated that the decay rate constants of the reactant complex in the product direction and in the reactant direction did not represent statistical values. This constitutes a... 

Modem methods based on density-functional theory (DFT) can describe relative activation barriers of organometallic reactions, i.e. relative reactivities, as well as the transition-metal NMR chemical shifts of the reactant complexes involved. It is thus possible to reproduce or rationalize observed correlations between these properties or to predict new ones. NMR/reactivity correlations that could be reproduced theoretically ("intrinsic correlations") are summarized. Newly predicted NMR/ reactivity correlations are discussed for the ethylene polymerization with V(=0-X)R3 or V(=Y)R3 catalysts. When X or Y are varied (X = A1H3, Li+, SbF5, H+ Y = NH, O, S, Se), both... 

Figure 1 H2OH+Cl ClONCh tTpOls reactant complex...

Investigation of this reaction isolated in an N2 matrix at 10-20 K has shown that the apparent activation energy is smaller than 0.11 kcal/mol the unimolecular rate constant for N0-03 reactant complexes prepared in this way is 1.4 x 10-5 s-1 at 12 K. Experiments carried out using ozone enriched with 180 have revealed no observable isotope effect. 

Calculations have been carried out on the. S n2 reactions between chloride ion and methyl chloride or chlorosilane at several DFT levels of theory up to the OLYP/TZ2P level.102 The OLYP/TZ2P method gave much better (excellent compared with the CCDD(T)/aug-cc-pVQZ level) values than the other density functionals for both the geometry and the energies of the reactant complex and transition state for the methyl chloride reaction and the stable transition complex that forms in the chlorosilane reaction. 

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