Transitions between major conformational wells

The manifest linearity of the majority of free energy plots is paradoxical because the constant slope would indicate that the transition structure is substituent independent. Variation in structure might be expected to occur due to the change in substituent and thus yield curved relationships as indicated in Section 6.1. The relationship between reactivity and selectivity is based on a very simple model, to which most reactions do not conform because they involve not only at least two major bonding changes but solvation changes as well. 

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