In the Pericyclic Reactions Oxford Primer it is written that:
Pericyclic Reactions by Ian Fleming it is written that the deuterium substitution of the hydrogen atoms in the diene and dienophile that participate in a possibly Diels-Alder reaction, gives rise to inverse secondary isotope effect (as the carbon atoms change from trigonal to tetrahedral geometry):
-If both bonds are forming at the same time, the isotope effect when both ends are deuterated is geometrically related to the isotope effect at each end.
-If the bonds are being formed one at a time, the isotope effects are arithmetically related.
If both bonds are forming at the same time, the isotope effect when both ends are deuterated is geometrically related to the isotope effect at each end.
If the bonds are being formed one at a time, the isotope effects are arithmetically related.
I don't understand the principle behind this. Why does the isotope effect occur and how does it tell us whether the mechanism is radical or pericyclic? I need an answer much more concise than what is presented in the book.