Shielding—The phenomenon of atoms pushing electron density toward surrounding atoms; in NMR
spectroscopy, pulls a group further upfield on the spectrum.
Sigma (σ) bond—The bonding molecular orbital formed by head-to-head or tail-to-tail overlap of
atomic orbitals; all single bonds are sigma bonds.
Simple distillation—Distillation without any special features; can be used to separate liquids that
boil below 150°C and that have at least a 25°C difference in boiling points.
Size-exclusion chromatography—A special type of column chromatography in which the beads in
the column contain tiny pores of varying sizes, slowing down small compounds that enter the
beads.
sp—A hybrid orbital with 50% s-character and 50% p-character.
sp^2 —A hybrid orbital with 33% s-character and 67% p-character.
sp^3 —A hybrid orbital with 25% s-character and 75% p-character.
Specific rotation ([α])—A standardized measure of a compound’s ability to rotate plane-polarized
light.
Spectroscopy—Laboratory technique that relies on measurement of the energy differences
between the possible states of a molecular system by determining the frequencies of
electromagnetic radiation (light) absorbed by the molecules or response to a magnetic field.
Spin quantum number (ms)—Describes the intrinsic spin of the two electrons in an orbital by
arbitrarily assigning one of the electrons a spin of and the other a spin of .
Spotting—In thin-layer chromatography, placing the sample directly onto the adsorbent as a small,
well-defined spot.
Staggered conformation—When a molecule has no overlapping substituents along the line of sight
between two carbons, as in a Newman projection.