Volume of Activation and Mechanism

The volume of activation is probably the easiest parameter to understand conceptually. Consider again the water exchange of Cr(lll), Sec. 2.3.3. The AF value of —10 cm mol for Cr(H20)g+ indicates that an associative process pertains (If) since CrflljO) plus one H2O will occupy more volume than the activated complex which has seven waters associated with the Cr. The volume of coordinated water has been estimated as anywhere between 5 and 9 cm moC, so that AK — 9 cm mol for an associative mechanism. Conversely, the value of +2.9 cm moC for water exchange on Cr(H20)50H + suggests a dissociative activation mode for the exchange.More success in interpreting AK values is likely for reactions in which the is small, or at least a small component of the overall AFjj,. The 

Reactants AK- cm mol Conclusions Technique with high pressure Ref. 

Racemization of Range from 3.3 Consistent with Batch 168 

High Spin AVf solvent dependent volumes for high  

N tion state geometry intermediate between spin isomers  

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