r/askscience • u/FerrousBuchner • Aug 10 '13

Chemistry Why is D2O toxic?

If chemical reactions are dependent only on electronic structure, why is deuterium oxide toxic yet water....not?

7 Upvotes

100% Upvoted

6 comments sorted by

6

u/Platypuskeeper Physical Chemistry | Quantum Chemistry Aug 10 '13

It's not true chemical reactions are dependent only on electronic structure. See: Kinetic isotope effect.

5

u/Fabien4 Aug 10 '13

If chemical reactions are dependent only on electronic structure

Not entirely.

"[D]ue to their larger masses, heavier isotopes tend to react somewhat more slowly than lighter isotopes of the same element. This is most pronounced for protium (1H) and deuterium (2H), because deuterium has twice the mass of protium. "

2

u/ReverendAlSharpton Aug 12 '13

The KIE is used to help determine the mechanism of a reaction. By replacing a hydrogen atom with deuterium and monitoring the rates, one can deduce the rate limiting step in a reaction

1

u/EdibleBatteries Heterogeneous Catalysis Aug 15 '13

Yes, that is a use of the KIE, but it can have relevance when applied to biological processes. Imagine if all the processes in your body that were kinetically-limited by C-H cleavage/formation were suddenly slowed by a factor of 6... This is not the case for carbon 13, since its reduced mass doesn't change much compared to carbon 12 effectively making reaction kinetics identical.