Dynamic resonances reaction

Lopez-Quintela MA (2003) Synthesis of nanomaterials in microemulsions formation mechanisms and growth control. Curr Opin Colloid Interface Sci 8 137-144 Lopez-Quintela MA, Tojo C, Blanco MC, Rio LG, Leis JR (2004) Microemulsion dynamics and reactions in microemulsions. Curr Opin Colloid Interface Sci 9 264-278 Maitra A (1984) Determination of Size Parameters of Water Aerosol Ot Oil Reverse Micelles from Their Nuclear Magnetic-Resonance Data. J Phys Chem 88 5122-5125... 

The dynamics of a reaction that proceeds directly over the transition state is expected to be qualitatively different from that of a resonance-mediated reaction. In particular, one expects that the branching ratios into the product rovibrational states will be very different between the direct and the resonant mechanisms. For example, if a given Feshbach resonance corresponds to trapping on the v = 1 vibrationally adiabatic curve, then one might expect that the population of the v = l vibrational state of the product molecule may be greatly enhanced by the resonant mechanism. Similarly, the rotational product distribution resulting from the fragmentation of a resonance molecule may show a quite distinct pattern from that of a direct reaction. Indeed, Liu and coworkers [94], and Nesbitt and coworkers [95] have noted distinct rotational patterns in the F+HD resonant reaction. 

X.M. Yang, D.H. Zhang, Dynamical resonances in the fluorine atom reaction with the hydrogen molecule, Acct. Chem. Res. 41 (2008) 981. 

Even with these limitations, nuclear magnetic resonance has made significant contributions to four areas of the chemistry of the platinum group metals bonding problems, molecular stereochemistry, solvation and solvent effects, and dynamic systems—reaction rates. Selected examples in each of these areas are discussed in turn. Because of space limitations, this review is not meant to be comprehensive. 

Basic Silicate Solutions Dynamics. Exchange reactions between silicates as well as zeolite formation involve condensation and hydrolysis reactions between dissolved silicate species. Therefore, we have extensively studied the dynamics of basic silicate solutions in order to obtain better knowledge of the properties of possible zeolite precursor species. Our first results were published earlier (11). Here we have again used selective excitation Si-NMR experiments, applying DANTE-type (13) pulse sequences to saturate a particular Si resonance belonging to a particular Si site. The rate of transfer of magnetization from this saturated site to other sites is then a measure of the chemical exchange rate between the two sites. 

Dynamic Resonances in the Reaction of Fluorine Atoms with Hydrogen Molecules... 

In light of previous experimental and theoretical work on the F f H2 reaction, it can be seen why an experisient of this complexity is necessary in order to observe dynamic resonances in this reaction. The energetics for this reaction and its isotopic variants are displayed in Figure 1. Chemical laser (11) and infrared chemiluminescence (12) studies have shown that the HF product vibrational distribution is hi ly inverted, with most of the population in v=2 and v°°3. A previous crossed molecular beam study of the F + D2 reaction showed predominantly back-scattered DF product (13). These observations were combined with the temperature dependence of the rate constants from an early kinetics experiment (14) in the derivation of the semiempirical Muckerman 5 (M5) potential energy surface (15) using classical trajectory methods. Although an ab initio surface has been calculated (16), H5 has been the most widely used surface for the F H2 reaction over the last several years. 

In this paper, we will present a detailed analysis of the way In which resonances may affect the angular distribution of the products of reactive collisions. To do this, we have used an approximate three-dimensional (3D) quantum theory of reactive scattering (the Bending-Corrected Rotating Linear Model, or BCRLM) to generate the detailed scattering Information (S matrices) needed to compute the angular distribution of reaction products. We also employ a variety of tools, notably lifetime matrix analysis, to characterize the Importance of a resonance mechanism to the dynamics of reactions. 

Fulling and Sih reported one of the earliest examples to exploit racemization of carboxylic acid derivatives in order to achieve a dynamic kinetic resolution1311. The anti-inflammatory drug Ketorolac was prepared by hydrolysis of the corresponding ester. Whilst most lipases afforded the undesired enantiomer preferentially, a protease from Streptomyces griseus afforded the required (S)-enantiomer of product with good selectivity. The substrate was particularly prone to racemization since the intermediate enolate is well stabilized by resonance effects, although a pH 9 7 buffer was required to achieve a useful dynamic resolution reaction. Thus the acid was formed with complete conversion and with 76 % enantiomeric excess. 

Fig. 1.1 One-dimensional views of two model reactions, a reaction with a simple barrier and a typical reaction with a dynamical resonance a the potential energy curve along the reaction coordinate for a model reaction with a simple barrier b the calculated reaction probability and time delay for the model reaction in panel a c the potential energy curve along the reaction coordinate for a model reaction with a dynamical resonance d the calculated reaction probability and time delay for the model reaction in panel c. The two reaction models are adapted from ref. [22], Reprinted with the permission from Ref. [23]. 2008 American Chemical Society...

In Feshbach resonance system, the reaction coordinate couples with the other freedom degrees. The system can form a quasi-bound or metastable complex, which is Feshbach resonance, also known as dynamic resonance. Even in pure repulsion potential energy surface, this resonance state can be formed. Quasi-bound complex can react with other adiabatic potential surface, producing non-adiabatic coupling dissociation product (Fig. 1.3) [11]. In F -h H2reaction, Feshbach resonance results forward scattering, producing HF (v = 2), see Chap. 3 of this thesis. 

We systematically studied the F( P3/2) + H2 HF + H reaction and found that the product HF(v = 2) has obvious forward scattering. The experimental finding of reaction resonance in this system, combined with the theoretical calculations from Daiqian Xie and Donghui Zhang et al. gave a perfect answer to the question whether reaction resonance exists in this system. We also pictured resonance reaction mechanism for this system. Moreover, we studied the dynamical effects of the H2 rotation in the reaction, analyzed how the H2 rotation affects reaction resonance, and gave a clear physical picture, to further enrich the content of the reaction resonance. 

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