(degenerate) equilibrium between two (except for iso-
topic substitution) species that are equivalent. This can
be used to distinguish a rapidly equilibrating mixture
with time-averaged symmetry from a single structure
with higher symmetry.
See also NUCLEAR MAGNETIC RESONANCE SPEC-
TROSCOPY.
isotopic scrambling The achievement, or the pro-
cess of achieving, an equilibrium distribution of iso-
topes within a specified set of atoms in a CHEMICAL
SPECIESor group of chemical species. For example:
(* denotes position of an isotopically different atom.)
See alsoFRACTIONATION FACTOR, ISOTOPIC.
isotopologue A MOLECULAR ENTITYthat differs only
in isotopic composition (number of isotopic substitu-
tions), e.g., CH 4 , CH 3 D, CH 2 D 2 ....isotopomer Isomers having the same number of each
isotopic atom but differing in their positions. The term
is a contraction of “isotopic isomer.”
Isotopomers can be either constitutional isomers
(e.g., CH 2 DCHO and CH 3 CDO) or isotopic
stereoisomers (e.g., (R)– and (S)–CH 3 CHDOH or (Z)–
and (E)–CH 3 CHCHD).isotropy Lack of ANISOTROPY; the property of
molecules and materials of having identical physical
properties in all directions.isovalent hyperconjugation See HYPERCONJUGA-
TION.150 isotopic scrambling