isotopolog

An isotopolog is a molecule that differs from another molecule only in the isotopic composition of its constituent atoms. Essentially, it's the same chemical compound, but with some atoms replaced by their heavier or lighter isotopes. For example, if water (H2O) has both hydrogen atoms replaced by deuterium (an isotope of hydrogen with one proton and one neutron), the resulting molecule D2O, known as heavy water, is an isotopolog of H2O. Similarly, if one oxygen atom in CO2 is replaced by the isotope oxygen-18, the resulting molecule C18O2 is an isotopolog of C16O2.

The chemical properties of isotopologs are very similar to their non-isotopolog counterparts because chemical reactions primarily depend on the number of electrons and the arrangement of atoms, which are largely unaffected by the mass of the isotopes. However, there can be subtle differences in reaction rates, known as kinetic isotope effects, due to the mass difference influencing bond vibrations and transition states. This subtle difference can be exploited in analytical chemistry and scientific research. Isotopologs are important in various fields, including metabolic studies, environmental tracing, and nuclear magnetic resonance (NMR) spectroscopy, where they can be used to track the fate of specific atoms or molecules within complex systems.