Degree of bond-making

The above evidence shows that a high degree of bond-making in the rate-determining step of bimolecular nucleophilic substitutions seems... 

In solution the situation is more complicated still, because the solvent can play a more or less active role in the reaction. For example, solvent turns out to be involved to some extent as a nucleophile in many SNl-type processes, where highly electrophilic intermediates are involved (Lowry and Richardson, 1987, pp. 335 ff.). Here a degree of bond making accompanies what had originally been regarded as uncomplicated rate-determining bond-breaking reactions. 

It is interesting to attempt to extend this type of analysis in the direction of a more quantitative assessment of the degree of bond-making or breaking in the... 

Scheme 2. Conformational changes of the y-phosphate in a) phosphoryl-transfer reaction transition state K), and various species of AlFx b) AlF41, c) A1C13. Dotted lines indicate that the degree of bond making and bond breaking determines whether the transition is more dissociative, with a metaphosphate-like intermediate, or associative, with a pentavalent intermediate. Charges have been omitted for clarity. N = adenosine or guanosine. According to [16, 17, 21]...

In the next section, we cite information that shows that substitution reactions of reactive phosphate monoesters occur with inversion of relative configuration at phosphorus. That stereochemical outcome is consistent with this interpretation since both nucleophile and leaving group must bond to phosphorus at the same time. The small degree of bond-making and the large extent of bond-breaking in the transition state is consistent with a... 

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