Stationary phase—A solid medium onto which a sample is placed for chromatography; also called
the adsorbent.
Stereogenic—Describes a chiral center in a molecule.
Stereoisomers—Isomers that have the same chemical formula and the same atomic connectivity,
but differ in how atoms are arranged in space; any isomer that is not a structural isomer is a
stereoisomer.
Stereoselective—A reaction that forms an unequal distribution of isomer products that is
determined by stability of those products.
Stereospecific—A reaction that preferentially yields a specific conformation of product, such as SN2
reactions
Steric hindrance—The prevention of a reaction at a particular location in a molecule by substituent
groups around the reactive site.
Steric protection—The prevention of the formation of alternative products using a protecting
group.
Strecker synthesis—A method of synthesizing amino acids that uses condensation between an
aldehyde and hydrogen cyanide, followed by hydrolysis.
Structural isomers—Molecules that have the same molecular formulas but different connectivity;
also called constitutional isomers.
Substituent—Any functional group that is not part of the parent chain.
Tautomer—An isomer that differs from another by the placement of a proton and a double bond.
Tetramethylsilane (TMS)—The calibration standard that marks 0 ppm when plotting an NMR
spectrum.
Thin-layer chromatography (TLC)—A type of chromatography that uses silica gel or alumina on a
card as the medium for the stationary phase.