Cyclopentenones molecular orbital calculations

Molecular orbital calculations have suggested that cyclopentenone is intrinsically more x one to conjugate reduction than cyclohexenone " and thus is a good substrate on which to test new 1,2-selective reagents. The selectivity of reduction of both these enones with the best of the new reagents together with the results for 9-BBN-H, the previous reagent of choice, are tabulated for comparison (Table 2). 

Cyclopentenone invariably gives more 1,4-addition products than cyclo-hexenone does in hydride reduction as well as in many other reactions. By ab initio calculations, it can be shown that the lowest unoccupied molecular orbital of cyclopentenone is 6.9 kcal lower in energy than cyclohexenone. As a consequence, the interaction at C-4 of cyclopentenone with soft bases is always stronger. 

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