α-

a prefix designating (1) the carbon atom adjacent to the principal functional group, e.g., α-amino acids, succeeding letters, β, γ, δ, etc., being used to designate succeeding carbon atoms in the chain; (2) the specific rotation of an optically active substance, e.g., α-D-glucose; (3) the orientation of an exocyclic atom or group, e.g., 3α-hydroxy-5α-androstan-17-one (androsterone); (4) a plasma protein migrating with the α band (subdivided into α₁ and α₂ bands) in protein electrophoresis, e.g., α-fetoprotein; (5) one in a series of related chemical compounds, particularly a series of stereoisomeric, isomeric, polymeric or allotropic forms, e.g., α-carotene; and (6) one in a group of related entities, e.g., α-ray. For compounds prefixed with the symbol α-, see the unprefixed form.