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Why does the transition state in both protonated and deuterated molecules have the same energy? My textbook assumes that during transitional state the isotopic bond is half-broken or on its way to break

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  • $\begingroup$ The electronic contribution to the transition state is the same but the isotopes have different zero point vibrational energy both in reactants and at the transition state and this changes the actual energy needed between different isotopes. The effect is generally only important in H isotopes. $\endgroup$ – porphyrin Jul 4 at 17:49
  • $\begingroup$ @porphyrin this means that transition state in deuterated molecules absorb more energy then why it isn't of higher energy than the protonated molecules in potential energy diagrams , the deuterated transition state molcules should be less stable during bond breaking $\endgroup$ – mohamed Jul 5 at 13:35
  • $\begingroup$ No: the only difference is in the amount of zero point vibrational energy in the reactants (H vs D), and then H vs D at the transition state. There is no absorption of energy but only energy needed in reactants to surmount the transition state. The electronic part is the same in H vs D molecules. $\endgroup$ – porphyrin Jul 5 at 14:59

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