Chemoselectivity is the preferential reaction of a chemical @[email protected] with one of two or more different functional groups. A @[email protected] has a high chemoselectivity if reaction occurs with only a limited number of different functional groups. For example, sodium tetrahydroborate is a more chemoselective reducing agent than is lithium tetrahydroaluminate. The concept has not been defined in more quantitative terms. The term is also applied to reacting molecules or intermediates which exhibit @[email protected] towards chemically different reagents. Some authors use the term @[email protected] for 100% chemoselectivity. However, this usage is discouraged.