Examples for Reaction Predictions

The important question is how good the reactivity functions are when applied in EROS to real problems, centered on molecules other than those whose parameters and properties led to its derivation. For this purpose, we now return to the problems 

A summary of EROS s results for the reaction of the hydroxynorbomene, 4, under basic conditions is given in Fig. 29. In practice, the experiment was performed with the potassium salt in HMPT solution 

In practice, fragmentation of exactly this kind is observed under basic conditions, to give IS in 45% isolated yield along with less than 10% 77 . (With alkyl groups other than the methyl substituent the ratio of 2- to 3-cyclopentenyl isomers can rise to 40 60.) The reactivity functions in EROS evaluate these products quite highly. The enthalpy of reaction is also realistic at —2.5 kcal/mol for both products. This value is more favorable than those for the other possible products suggested. 

What of the other suggested products in Fig. 29 The RG33-type fragmentation leading to 20 is still formally permitted by EROS. However, orbital symmetry constraints suggest that such a reaction would not occur in practice. As yet, EROS pays no heed to this type of orbital overlap consideration, which depends on knowledge of stereochemistry and conformation. 

The starting hydroxynorbomene, 4, contains 22 bonds, of which 18 are constitutionally distinct. There are therefore 36 distinct single bond heterolyses. Application of RG22 to all possible bond combinations leads to at least 864 possible reactions RG33 can give t least 10,000 possible reactions Thus, to summarize, EROS s evaluations not only reduce a totally intractable number of formal possibilities to five feasible products, it also suggests, correctly, which of these are the most likely. 

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