Theory of reactivity

Baer M 1985 The general theory of reactive scattering the differential equations approach Theory of... 

Poliak E 1985 Periodic orbits and the theory of reactive scattering Theory of Chemical Reaction Dynamics vol III, ed M Baer (Boca Raton, FL CRC Press)... 

The electronic theory provides by these means a description of the influence of substituents upon the distribution of electrons in the ground state of an aromatic molecule as it changes the situation in benzene. It then assumes that an electrophile will react preferentially at positions which are relatively enriched with electrons, providing in this way an isolated molecule theory of reactivity. 

However, the electronic theory also lays stress upon substitution being a developing process, and by adding to its description of the polarization of aromatic molecules means for describing their polarisa-bility by an approaching reagent, it moves towards a transition state theory of reactivity. These means are the electromeric and inductomeric effects. 

No matter how thorough, a kinetic study does not really determine a mechanism in the same sense that single-crystal X-ray diffraction measurements determine a structure. The reaction mechanism is but a scientific postulate that is open to revision when new data, new insights, or new theories of reactivity emerge. 

In the final section of this chapter, we shall attempt to give a brief rationalization of the regularities and peculiarities of the reactions of non-labile complexes which have been discussed in the previous sections. The theoretical framework in which the discussion will be conducted is that of molecular orbital theory (mot). The MOT is to be preferred to alternative approaches for it allows consideration of all of the semi-quantitative results of crystal field theory without sacrifice of interest in the bonding system in the complex. In this enterprise we note the apt remark d Kinetics is like medicine or linguistics, it is interesting, it js useful, but it is too early to expect to understand much of it . The electronic theory of reactivity remains in a fairly primitive state. However, theoretical considerations may not safely be ignored. They have proved a valuable stimulus to incisive experiment. 

A further test of the stereoelectronic theory of reactivity of phosphate esters has been attempted using measurements of the rates of displacement of 4-nitrophenate from the esters (23) and (24), their phosphorus epimers, and also (25), in aqueous methanol the introduction of the 4a-Me group into the system would, it was hoped, reduce the the flexibility of the bicyclic structures and so possibly eliminate the participation of twist-boat conformations. The presence of the 4a-Me group has no effect of the rate of displacement of the axial ArO group... 

The aim here is to show the application of the simple theory of reactivity index along with some useful derivation of the theory in terms of resolving key issues. Some examples are provided to have an understanding of the applicability of this to industrial issues. Finally, a newest example of the application of reactivity index will performed to show the use of single-wall nanotube (SWNT) for gas sensing, and a... 

As in the case of photodissociation, the quantum theory of reactive molecular scattering was initially entirely based on time-independent scattering theory [4-7,100-123]. There were several early attempts to apply time-dependent quantum theory to reactive scattering processes [124—131]. But the modern era of the field really began with the seminal work of Kosloff et al. [37] and the subsequent application of his grid-based methods to the reactive scattering problem by Neuhauser and Baer and coworkers [45,132]. There have been many developments in the field [93,133-138], and several reviews and a book have been written on the topic [10,139-141]. My aim in the next section will be to outline the basic methods of time-dependent quantum theory used in reactive scattering calculations. While the review will cover many aspects of the theory, it will not cover all the approaches currently in use (as of 2003). 

The first part of the review deals with aspects of photodissociation theory and the second, with reactive scattering theory. Three appendix sections are devoted to important technical details of photodissociation theory, namely, the detailed form of the parity-adapted body-fixed scattering wavefunction needed to analyze the asymptotic wavefunction in photodissociation theory, the definition of the initial wavepacket in photodissociation theory and its relationship to the initial bound-state wavepacket, and finally the theory of differential state-specific photo-fragmentation cross sections. Many of the details developed in these appendix sections are also relevant to the theory of reactive scattering. 

Most of the previous results have been briefly summarized by Streit-wieser,3 who pointed out the special situation of positions adjacent to the heteroatom. A very thorough and critical review of a major portion of the studies just mentioned has been published by Ridd147 it seems useful to refer the reader to his paper and then concentrate on some additional aspects of the theory of reactivity of pyridine-like heterocyclic compounds. 

It should be stated at the beginning that despite quite numerous partial successes the present state of the quantum-chemical theory of reactivity is far from satisfactory. First of all, it is not clear whether the present shortcomings are due to the non-adequacy of models of activated complexes or to the drastic approximations made in the calculation of the energy of the activated complex and the reactants. On the other hand, some other deficiencies of most of the reported attempts to interpret reactivity in terms of the theory are obvious the very nature of the HMO method is thought148 to make it necessary to treat as large sets of theoretical and experimental data as possible and, in addition, to respect the distinction in properties of the three classes of positions mentioned (in this connection we do not refer to the difference in the stereochemistry of these positions). 

The quantum theory of reactive scattering is not as highly developed as for inelastic scattering. No generally applicable algorithm has yet been perfected, particularly for three-dimensional reactions. However, many promising approaches are being explored. 

D A Micha. Quantum theory of reactive molecular collisions. Adv. Chem. Phys., 30 7, 1975. 

The use of charge density as a criterion is based on another time-honored chemical idea, the electrostatic theory of reactivity. 

K. Fukui, T. Yonezawa, H. Shingu, J. Chem. Phys. 20, 722 (1952). A Molecular Orbital Theory of Reactivity in Aromatic Hydrocarbons. 

The theory of reactive collisions is dealt with in several recent texts. In particular, the works of Levine [118] and Child [119], two volumes edited by Miller [142] and a very comprehensive volume edited by Bernstein [120]. 

Alfrey and Price develop a semi-quantitative theory of "reactivity-ratios" in copolymerisation... 

Baer, M. (1985) The General Theory of Reactive Scattering The Differential Equation Approach, in M. Baer (ed.). Theory of Chemical Reaction Dynamics. Vol.l, CRC Press, Inc.,Boca Raton, pp.91-161. 

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