Hard-soft affinity inversion

Carbon - heteroatom bonds can be cleaved by an appropriate combination of a hard acid and a soft nucleophile. Synthetically useful selective C-0 bond cleavage in the presence of other C-0 bond(s) is described. Reductive dehalogenation of a-haloketones is presented as an example that illustrates the concept of hard-soft affinity inversion. Finally, regio- and stereoselective functionalization of 1,3-di-enes is demonstrated by the thienium cation Diels-Alder cyclization involving the C-S bond cleavage. 

Carbon-Halogen Bond Cleavage Hard-Soft Affinity Inversion... 

The second derivative of the energy with respect to the number of electrons is the hardness r) (the inverse quantity is called the softness), which again may be approximated in term of the ionization potential and electron affinity. 

Hence, it is clear that fundamentally and operationally the physico-chemical process of protonatirMi can be linked to the above akin descriptors — the ionization process, the hardness, softness, electronegativity and electrophilicity. Recently, we (Islam et al. 2010, 2011a, b Ghosh et al. 2011a) have published good number of papers where we have discussed that the three descriptors, the electronegativity, the hardness and the electrophilicity index of atoms and molecules are fundamentally qualitative per se and operationally the same. All three represent the attraction of screened nuclei towards the electron pair/bond. Thus, we can safely and reasonably conclude that the proton affinity and the three descriptors have inverse relationship. 

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