Preferred Label : secondary isotope effect;
IUPAC definition : A kinetic isotope effect that is attributable to isotopic substitution of an atom
to which bonds are neither made nor broken in the rate-controlling step or in a pre-equilibrium
step of a specified reaction, and is therefore not a primary isotope effect. One speaks
of α, β, (etc.) secondary isotope effects, where α, β, (etc.) denote the position
of isotopic substitution relative to the reaction centre. The corresponding isotope
effect on the equilibrium constant of such a reaction is called a 'secondary equilibrium
isotope effect'. Secondary isotope effects have been discussed in terms of the conventional
electronic effects of physical organic chemistry, e.g. induction, hyperconjugation,
hybridization, etc., since these properties are determined by the electron distribution,
that depends on vibrationally averaged bond lengths and angles which vary slightly
with isotopic substitution. While this usage is legitimate, the term 'electronic isotope
effect' should be avoided, because of the misleading implication that such an effect
is electronic rather than vibrational in origin.;
Origin ID : S05523;
See also
A kinetic isotope effect that is attributable to isotopic substitution of an atom
to which bonds are neither made nor broken in the rate-controlling step or in a pre-equilibrium
step of a specified reaction, and is therefore not a primary isotope effect. One speaks
of α, β, (etc.) secondary isotope effects, where α, β, (etc.) denote the position
of isotopic substitution relative to the reaction centre. The corresponding isotope
effect on the equilibrium constant of such a reaction is called a 'secondary equilibrium
isotope effect'. Secondary isotope effects have been discussed in terms of the conventional
electronic effects of physical organic chemistry, e.g. induction, hyperconjugation,
hybridization, etc., since these properties are determined by the electron distribution,
that depends on vibrationally averaged bond lengths and angles which vary slightly
with isotopic substitution. While this usage is legitimate, the term 'electronic isotope
effect' should be avoided, because of the misleading implication that such an effect
is electronic rather than vibrational in origin.
