Nascent hydrogen
Nascent hydrogen is purported to consist of a chemically reactive form of hydrogen that is freshly generated, hence nascent. Molecular hydrogen (H2), which is the normal form of this element, is unreactive toward organic compounds, so a special state of hydrogen was once invoked to explain certain kinds of hydrogenations. Mechanistic understanding of such reactions is now available, and the concept of nascent hydrogen is discounted, even ridiculed.