Clearly, the above diagrams depict the interaction between empty orbital of electrophile with filled orbital of nucleophile. We may assume that the HOMO of nucleophile being more electronegative will have energy less than that of less electronegative electophile as above.
As on the diagram on page 111 on Organic chemistry by Clayden, it is stated that the empty orbitals of Nu are too high in energy to interact with the electrophile. But if the HOMO energy is higher than the vacant orbital of electrophile will the reaction not be feasable?