Studying Organic Reaction Mechanisms

An organic reaction mechanism is a step-by-step description of the movement of electrons, and bond-making and bond-breaking processes, as well as an understanding of the nature of any intermediates that may be a part of the process. 

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As noted in Section 4.2.1, the gas phase has proven to be a useful medium for probing the physical properties of carbanions, specifically, their basicity. In addition, the gas phase allows chemists to study organic reaction mechanisms in the absence of solvation and ion-pairing effects. This environment provides valuable data on the intrinsic, or baseline, reactivity of these systems and gives useful clues as to the roles that solvent and counterions play in the mechanisms. Although a variety of carbanion reactions have been explored in the gas phase, two will be considered here (1) Sn2 substitutions and (2) nucleophilic acyl substitutions. Both of these reactions highlight some of the characteristic features of gas-phase carbanion chemistry. 

Introduction and overview - why study organic reaction mechanisms ... 

Conversely, a substance can be eliminated as an intermediate if it can be shown that the concentration of the substance in the reaction mixture must be less than would be required to produce the product at the observed rate. One way to do this utilizes the technique of isotopic dilution. For a discussion, see Swain, C. G. Powell, A. L. Sheppard, W. A. Morgan, C. R. /. Am. Chem. Soc. 1979, 101, 3576. A general discussion of the use of isotopes to study organic reaction mechanisms was given by Collins, C. J. Adv. Phys. Org. Chem. 1964, 2, 1. 

A common application of the direct calculation of molecular energy is the study of organic reaction mechanisms. You can investigate the energies of different potential intermediates, species not easily studied by experiment. A review by Thiel lists many such 39. Thiel, W. Semiempirical Methods Current Status and Perspectives Tetrahedron, 44 7393, 1988. 

CHAPTER 4 STUDY AND DESCRIPTION OF ORGANIC REACTION MECHANISMS... 

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