ABSTRACT
Many workers use quantitative steric and electronic parameters in linear freeenergy relationships, LFERs, in which kinetic or thermodynamic properties are correlated with the steric and electronic parameters (Eq. 1) (1-3):
(1)
where a, b, and c are constants and S and E are quantitative measures of steric and electronic effects, respectively. Each time an LFER is implemented, several pertinent questions arise. One of the most important is: Which steric and elec tronic parameter is most appropriate for my data set? In this chapter, we focus attention on the steric measure. There has been considerable attention given to the nature of quantitative steric measures in linear free-energy relationships. Re cently, sections of inorganic and kinetics texts have been devoted to a discussion of the quantitative steric measures (4,5). We will examine the theory behind the quantification of steric effects in organometallic chemistry. Each of the measures presented has certain advantages that make it more appropriate for specific types of linear free-energy relationships. If the assumptions behind the steric measure
are thoroughly understood, then deviations from linearity in the LFER are more easily understood, and the rationalizations for such deviations are more soundly based.
