CoachA hard nucleophile or hard electrophile is small, carries a concentrated charge and has a HOMO (respectively a LUMO) far from that of its partners: it reacts under charge control. A soft nucleophile or soft electrophile is large and polarisable, with a high HOMO (respectively a low LUMO): it reacts under orbital control. Hard reacts preferably with hard, soft with soft.
Chemistry · Glossary
What is Hard and soft species?
Also known as: hard nucleophile · hard electrophile · soft nucleophile · soft electrophile